16 Units · 469 Quiz Questions · 155 Flashcards · Diagnostic · Full Reference Tables · Diagrams · Saved Progress
Based on this guide's real question bank — 469 practice questions across 16 units. Slide to match your situation.
Rutherford gold-foil experiment — most α particles pass through (empty space); a few deflect off the dense positive nucleus.
Periodic trends: atomic radius grows ↓ and ←. Ionization energy and electronegativity grow ↑ and → (toward F in the top-right).
Molecular polarity: CO₂ is linear (symmetric → nonpolar); H₂O is bent (asymmetric → polar).
Heating curve: sloped = KE↑ (q=mCΔT); flat plateaus = phase change, PE↑, T constant (q=mH).
Solubility curve zones. On the line = saturated; below = unsaturated; above = supersaturated (unstable).
PE diagram: Ea = peak−reactants; ΔH = products−reactants. Dashed = catalyzed pathway (lower Ea, same ΔH).
Le Chatelier stresses: adding reactant → shift right; adding product → shift left; ↑T for exo → shift left; ↑P → shift toward fewer gas moles.
Voltaic cell: anode (−) = oxidation; cathode (+) = reduction. Electrons flow anode→cathode via wire; ions flow through salt bridge.
Radioactive decay types: alpha loses ⁴₂He (mass−4, Z−2); beta emits e⁻ (Z+1); gamma emits photon (no change); penetrating power: γ > β > α.
Which sample is a pure substance?
N₂ is a pure substance (element). Salt water, air, and granite are mixtures.
Which separation technique separates two liquids with different boiling points?
Distillation separates based on different boiling points.
Dissolving salt in water is best classified as a physical change because the
Dissolving is physical — NaCl is still NaCl. Evaporate the water and the salt is recovered unchanged.
Which is a chemical change?
Rusting is a chemical change (Fe + O₂ → Fe₂O₃). A new substance with new properties forms.
Which statement correctly describes the property of density?
Density is an intensive property — a small gold ring and a large gold bar have the same density.
Which is an extensive property?
Mass depends on the amount of substance present → extensive.
Heterogeneous mixtures can be identified because they:
Heterogeneous mixtures have visibly different parts (e.g., salad, granite).
Which process separates ink pigments by polarity?
Chromatography separates substances based on their polarity/affinity for the stationary phase.
Which is a physical property?
Boiling point is observable without changing the substance's identity.
A compound differs from a mixture because a compound:
Compounds have fixed ratios of elements, chemically bonded. Mixtures have variable composition.
Which substance is an example of a homogeneous mixture?
Brass is a homogeneous mixture (alloy) — uniform throughout at the macroscopic level.
What evidence indicates a chemical change occurred?
Gas production indicates new substances formed → chemical change.
Filtration is used to separate:
Filtration separates insoluble solids (like sand) from liquid (like water).
Which is a chemical property?
Flammability describes HOW a substance reacts (combustion) → chemical property.
The Tyndall effect (light scattering) is characteristic of a:
Colloids scatter light (Tyndall effect); true solutions do not.
Which change requires breaking chemical bonds?
Burning involves breaking C-H bonds and forming new bonds (CO₂, H₂O) → chemical change.
A pure substance can be classified as either:
Pure substances are either elements (one atom type) or compounds (chemically bonded elements).
Centrifugation separates components based on differences in:
Centrifugation uses centrifugal force to separate by density differences.
Which substance cannot be broken down by chemical means?
Carbon is an element — cannot be broken down chemically into simpler substances.
Color change during a reaction most likely indicates:
Color change (new substance forming) is a sign of a chemical change.
O₂ and O₃ are both forms of the element oxygen. These two substances have:
O₂ and O₃ are allotropes — same element, but different molecular structures → different chemical and physical properties.
Which phrase best describes a compound?
A compound is two or more elements chemically combined in fixed ratios. It can only be separated by chemical means.
When a molecule of H₂ and a molecule of I₂ collide with proper orientation and sufficient energy, the most likely result is
H₂ + I₂ → 2HI: a new compound (HI) forms. New substance with different properties = chemical change.
A mixture of crystals of salt and sugar is dissolved in water. Which statement best describes the resulting mixture?
The resulting solution is homogeneous (uniform throughout). Since both solids dissolved, filtration would not separate them — both pass through filter paper.
Distillation of crude oil from various parts of the world yields different percentages of hydrocarbons. Which statement explains this?
Crude oil is a mixture. Mixtures have variable proportions — crude oil composition differs by location.
When a mixture of water, sand, and salt is filtered, what passes through the filter paper?
Sand is insoluble and is caught by the filter. Salt and water (solution) pass through. Answer: water and dissolved salt.
How many significant figures are in 0.00240?
Leading zeros are never sig figs. Trailing zero after decimal IS significant. 2, 4, 0 → 3 sig figs.
How many sig figs in 1500.?
The decimal point makes all trailing zeros significant: 1, 5, 0, 0 = 4 sig figs.
A measurement of 12.5 + 3.45 should be reported as:
Add/subtract: round to fewest decimal places. 12.5 has 1 decimal → answer = 16.0.
2.5 × 3.45 = ? (correct sig figs)
Multiply: fewest sig figs is 2 (in 2.5) → 8.6.
A student measures 9.8 g; accepted value is 10.0 g. % error is:
|9.8−10.0|/10.0 × 100 = 0.2/10.0 × 100 = 2%.
How many moles are in 36.0 g of water (H₂O, GFM=18.0)?
n = m/GFM = 36.0/18.0 = 2.0 mol.
How many particles are in 2.0 mol of CO₂?
2.0 mol × 6.02×10²³ = 1.20×10²⁴ molecules.
The gram formula mass (GFM) of NaCl (Na=23, Cl=35.5) is:
GFM = 23 + 35.5 = 58.5 g/mol.
Measurements that are close to each other but far from the true value show:
Close to each other = precise; far from true = inaccurate. High precision, low accuracy.
0.000345 in scientific notation is:
Move decimal 4 places right → 3.45×10⁻⁴.
How many grams are in 3.0 mol of NaOH (GFM = 40.0 g/mol)?
g = mol × GFM = 3.0 × 40.0 = 120 g.
How many sig figs are in 2005?
Captive zeros (between nonzero digits) are always significant: 2, 0, 0, 5 = 4 sig figs.
% error is always:
% error uses absolute value — always positive (deviation from accepted value).
How many atoms are in 1 mole of O₂?
1 mol O₂ = 6.02×10²³ molecules. Each has 2 O atoms → 1.20×10²⁴ O atoms.
GFM of Ca(OH)₂ (Ca=40, O=16, H=1) is:
40 + 2(16+1) = 40 + 34 = 74 g/mol.
Trailing zeros in 1500 (no decimal) are:
Without a decimal, trailing zeros are ambiguous. Scientific notation clarifies: 1.5×10³ (2 s.f.) or 1.500×10³ (4 s.f.).
Which instrument measures the most precise volume?
A buret has the smallest gradations and reads to 0.01 mL — most precise.
A student gets 9.5, 9.4, 9.6 g (accepted = 12.0 g). The results are:
Results cluster closely (precise) but are far from 12.0 (not accurate).
The number of moles in 6.02×10²³ molecules of glucose is:
By definition, 6.02×10²³ particles = 1 mole.
If D = m/V and m = 24 g and V = 8 mL, D equals:
D = 24/8 = 3.0 g/mL.
Which kelvin temperature is equivalent to −24°C?
K = °C + 273 = −24 + 273 = 249 K.
Which measurement contains exactly three significant figures?
120. — the decimal point makes all three digits significant (1, 2, 0). Without the decimal, trailing zeros are ambiguous.
A student measures 22.5 g of H₂O in an 8.28 mL sample. What is the density, to the correct number of significant figures?
D = m/V = 22.5 g ÷ 8.28 mL = 2.717... g/mL. Both measurements have 3 sig figs, so the answer is rounded to 3 sig figs → 2.72 g/mL.
When 1.255 g of X reacts with 3.2 g of Y, only product Z forms. What is the total mass of Z to the correct number of significant figures?
Conservation of mass: 1.255 + 3.2 = 4.455 g. Rounded to fewest decimal places in addition: 3.2 has 1 decimal place → 4.5 g.
The atomic number of an element equals the number of:
Atomic number = proton count = electron count in a neutral atom.
Two atoms are isotopes if they have the same:
Isotopes have the same atomic number (protons) but different mass numbers (different neutrons).
How many neutrons are in ⁸⁰₃₅Br?
Neutrons = mass number − atomic number = 80 − 35 = 45.
An atom in the excited state has:
Excited = one or more electrons at higher energy level than ground state. Total count same.
Rutherford's gold foil experiment showed that:
Most alpha particles passed through → atoms are mostly empty space; few deflected → small dense positive nucleus.
The atomic mass of an element is a:
Atomic mass = weighted average based on relative abundance of all naturally occurring isotopes.
Chlorine-35 has 17 protons. How many neutrons?
Neutrons = 35 − 17 = 18.
The current atomic model describes electrons as:
The wave-mechanical model: electrons exist in orbitals — regions of probability, not fixed paths.
In a bright-line spectrum, each line represents:
When an excited electron falls to a lower energy level, it emits a photon of specific wavelength → bright line.
The fill order 1s 2s 2p 3s 3p 4s 3d 4p shows that 4s fills:
4s has lower energy than 3d during filling → 4s fills BEFORE 3d.
Which subshell holds a maximum of 6 electrons?
p sublevel has 3 orbitals × 2 electrons each = 6 max.
Thomson's plum pudding model was replaced because:
Rutherford proved the nuclear model — most mass/charge concentrated in a tiny nucleus, not spread throughout.
An ion of Na has 11 protons and 10 electrons. Its charge is:
11 protons (+ charges) − 10 electrons (− charges) = net +1 → Na⁺.
Which has the highest energy per photon in the visible spectrum?
ROYGBIV: violet is highest frequency → shortest wavelength → most energy per photon.
Carbon-12 and Carbon-14 are isotopes. They differ in:
Same protons (6) → same element; different mass numbers (12 vs 14) → different neutron counts.
What is the maximum number of electrons that can occupy the d sublevel?
The d sublevel: 5 orbitals × 2 electrons = 10 max.
Electron configuration 1s²2s²2p⁶3s²3p³ describes which element?
Count electrons: 2+2+6+2+3 = 15 electrons → element #15 = Phosphorus (P).
In the EM spectrum, which has the shortest wavelength?
Gamma rays have the highest frequency and shortest wavelength → most energy.
An atom's electron configuration is 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s¹. This atom most likely is:
Count electrons: 2+2+6+2+6+2+10+6+1 = 37 electrons → element 37 = Rubidium (Rb).
Dalton's atomic model depicted atoms as:
Dalton (1803): atoms are solid, indivisible spheres — no internal structure.
Which conclusion resulted directly from the gold foil experiment?
Rutherford's gold foil experiment: most α particles passed through → mostly empty space; few deflected → small, dense, positive nucleus.
An atom has 37 protons and 49 neutrons. How many electrons does it have in the neutral state?
Neutral atom: electrons = protons = 37.
In the wave-mechanical model, electrons are found in regions called:
Wave-mechanical model: electrons exist in orbitals — regions of probability, not fixed paths.
Which electron configuration represents a lithium atom in the excited state?
Ground state Li: 2-1 (shells 1 and 2). Excited state: an electron jumped to a higher shell. 1-2-1 has 4 electrons — wrong count. 2-2 has 4 electrons — wrong. 1-1-1 has 3 electrons and an electron in the 3rd shell → excited state for Li (3 electrons, but in higher-than-ground arrangement). Answer: 1-1-1.
In the ground state, ions of which two elements each have the same electron configuration as neon?
Ne has 10 electrons. Mg²⁺ loses 2 electrons (12−2=10); O²⁻ gains 2 electrons (8+2=10). Both are isoelectronic with Ne.
Which electron configuration represents a sulfur atom in an excited state? (Sulfur ground state: 2-8-6)
S has 16 electrons. Ground state = 2-8-6. An excited state has the same 16 electrons in a non-ground arrangement. 2-7-7 = 2+7+7 = 16 electrons, but an electron jumped from shell 3 to shell 2 → excited state.
An orbital is best described as a region in an atom where there is a high probability of finding
An orbital is a region of probability for finding an electron. It is NOT a fixed circular path.
Most alpha particles directed at the gold foil in Rutherford's experiment passed through because
Rutherford concluded that atoms are mostly empty space — which is why most alpha particles passed straight through without deflection.
Which particles are found in the nucleus of an argon atom?
The nucleus contains only protons and neutrons. Electrons are found in orbitals outside the nucleus.
Across a period from left to right, atomic radius:
More protons across a period pull electrons closer → decreasing atomic radius.
Which element has the highest electronegativity?
Fluorine has EN = 4.0 — highest of all elements. Located top-right of the periodic table.
Down a group, ionization energy:
Down a group: more electron shells = greater shielding = outer electrons held less tightly → lower IE.
Group 17 elements are called:
Group 17 = halogens: F, Cl, Br, I, At. 7 valence electrons. Form −1 ions.
Which group contains elements that are completely nonreactive?
Group 18 = noble gases: full valence shells → chemically inert (He, Ne, Ar, Kr, Xe, Rn).
Compared to a sodium atom, a sodium ion (Na⁺) has a
Na⁺ lost 1 electron. The same 11 protons now pull 10 electrons more tightly → smaller radius.
Metalloids are located along:
Metalloids (B, Si, Ge, As, Sb, Te) run along the staircase/zigzag line on the right side.
Which best explains why atomic radius decreases across a period?
Across a period: adding protons increases nuclear charge pulling all electrons in the same shell closer.
The trend in metallic character going down a group is:
Down a group: electrons farther from nucleus, easier to lose → increased metallic character.
Which element is a metalloid?
Silicon (Si) is a metalloid — along the staircase. Used in semiconductors.
Elements in the same group have similar chemical properties because they have:
Same group = same number of valence electrons → similar reactivity and bonding.
Chlorine (Cl) most commonly forms which ion?
Cl has 7 valence electrons → gains 1 to complete octet → forms Cl⁻.
Which property increases across a period (left to right)?
Ionization energy increases left to right (more protons hold outer electrons more tightly).
Compared to a chlorine atom, a chloride ion (Cl⁻) has a
Cl⁻ gained 1 electron. The same 17 protons now attract 18 electrons → larger atomic radius.
The Coulomb's Law force between nucleus and electrons decreases when:
F ∝ 1/r² — as distance (shells) increases, the nuclear pull on outer electrons decreases.
Which is a property of metals?
Metals are malleable (can be hammered), ductile (can be drawn into wire), and good conductors.
Alkali metals (Group 1) react vigorously with water to form:
2Na + 2H₂O → 2NaOH + H₂↑. Alkali metals react violently with water.
Transition metals are in Groups:
Transition metals occupy the d-block, Groups 3–12.
Na⁺, Mg²⁺, and F⁻ are isoelectronic. This means they:
All three have 10 electrons and the configuration 1s²2s²2p⁶ (same as Ne).
Which best predicts the charge of an aluminum (Al, Group 13) ion?
Al has 3 valence electrons → loses all 3 → Al³⁺.
At STP, a sample of potassium can be differentiated from rubidium based on:
Both K and Rb are solid metals at STP (same phase). Density is an intensive physical property that differs between the two and can be measured to tell them apart.
What is the chemical name for PdO?
O = −2, so Pd must be +2 for the compound to be neutral. Roman numeral II → palladium(II) oxide.
Which element in the formula X₂O would X most likely be?
X₂O means 2 X atoms balance 1 oxygen (charge −2) → each X = +1. Group 1 elements have +1 charge. Cs is Group 1.
On the periodic table, the number of protons in an atom of an element is indicated by its
Atomic number = number of protons. This is the fundamental definition of atomic number and element identity.
When an atom loses an electron, the atom's radius and charge both change. Which correctly describes this change?
Losing an electron: fewer electrons means same nuclear charge pulls remaining electrons more tightly → smaller radius; net positive charge → cation.
Which element has metallic bonds at room temperature?
Cesium is a metal → held together by metallic bonding (sea of delocalized electrons). Cl, S are nonmetals; Kr is a noble gas.
Which type of bond forms between sodium and chlorine?
Na (metal) + Cl (nonmetal), ΔEN = 3.0−0.9 = 2.1 ≥ 1.7 → ionic bond.
A bond between two identical atoms (e.g., Cl₂) is:
Identical atoms → same EN → ΔEN = 0 → equal sharing → nonpolar covalent.
In which compound does hydrogen bonding occur?
H-bond requires H bonded directly to F, O, or N. Only HF has H bonded to F.
CO₂ has polar bonds but is a nonpolar molecule because:
CO₂ is linear and symmetric → two C=O dipoles point in opposite directions → cancel → nonpolar molecule.
An ionic solid (e.g., NaCl) conducts electricity:
Ionic solids: ions are locked in lattice → can't conduct. Dissolved or molten: ions are mobile → conduct.
Which molecule is polar?
NH₃ is pyramidal with a lone pair → asymmetric → net dipole → polar molecule.
The 'sea of electrons' model describes:
Metallic bonding: delocalized valence electrons form a sea surrounding positive metal ion cores.
London dispersion forces are present in which type of substance?
LDFs are present in ALL molecules — polar and nonpolar. They're the only force in nonpolar molecules.
The molecular geometry of H₂O is:
H₂O: 2 bonding pairs + 2 lone pairs → bent geometry (~104.5°).
Which bond is the most polar?
F has EN = 4.0 (highest). H-F has the largest ΔEN → most polar bond among common bonds.
Which property is explained by metallic bonding?
Metals conduct electricity because of delocalized (free-moving) electrons in the metallic bond.
The electronegativity difference for a polar covalent bond is:
ΔEN 0.4–1.7 = polar covalent bond. Less than 0.4 = nonpolar covalent. ≥1.7 = ionic.
In a Lewis structure for H₂O, how many lone pairs are on oxygen?
O has 6 valence electrons. 2 used in bonds with H. Remaining 4 = 2 lone pairs.
Which substance has the strongest intermolecular forces?
H₂O has hydrogen bonding (H bonded to O) → strongest IMFs among these → highest BP.
Diamond (pure carbon) has a very high melting point because:
Diamond is a network covalent solid — every C is covalently bonded to 4 others in a 3D network → extremely high MP.
The molecular geometry around N in NH₃ is:
NH₃: 3 bonding pairs + 1 lone pair → trigonal pyramidal shape (the lone pair is NOT included in the geometry name).
Which substance has the highest boiling point due to hydrogen bonding?
H₂O has H-bonding (H bonded to O) → much stronger IMFs than the heavier H₂S, H₂Se, H₂Te which only have dipole/LDF.
A double bond between two atoms consists of how many shared electrons?
A double bond = 2 pairs of shared electrons = 4 electrons.
BF₃ has polar B-F bonds but is a nonpolar molecule. Why?
BF₃ is trigonal planar (120° symmetric) → 3 equal B-F dipoles cancel → nonpolar overall.
Which substance has the lowest boiling point?
CH₄ is a small, nonpolar molecule with only weak LDFs → lowest BP of these substances.
Which compound contains both ionic and covalent bonds?
KClO₂: K⁺ and ClO₂⁻ joined by ionic bond; inside ClO₂⁻ the Cl−O bonds are covalent. CaCl₂, Li₂S, MnO₂ have only ionic bonds (no polyatomic ions).
Which element has diatomic molecules that each contain a multiple (double) covalent bond?
O₂ contains a double bond (O=O). H₂, Br₂, I₂ contain only single bonds. N₂ has a triple bond.
Which formula represents an asymmetrical (polar) molecule?
HCl: two different atoms → unequal EN → polar bond AND asymmetric (linear with two different ends) → polar molecule. CO₂, Cl₂, CH₄ are all symmetric (nonpolar).
When N + N → N₂ occurs, what happens to energy?
Forming bonds ALWAYS releases energy (exothermic). N + N → N₂ involves forming the N≡N triple bond → energy released.
Which statement explains why CH₄ is a nonpolar molecule?
CH₄ has 4 equal C-H bonds arranged symmetrically (tetrahedral) → dipoles cancel → nonpolar. Symmetry is the key reason.
The bond between Br atoms in a Br₂ molecule is best described as
Br₂: same element, ΔEN = 0 → nonpolar covalent bond. Electrons are equally shared (not transferred).
A barium atom attains a stable electron configuration when it bonds with
Ba is in Group 2 → loses 2 electrons → Ba²⁺. Each Cl gains 1 electron → Cl⁻. Two Cl atoms are needed to balance the 2+ charge → BaCl₂.
Which type of bonding is present in a sample of an element that is malleable?
Malleability is a property of metals, explained by metallic bonding — the delocalized electron sea allows layers of ions to slide without breaking bonds.
GFM of SO₂ (S=32, O=16) is:
GFM = 32 + 2(16) = 32 + 32 = 64 g/mol.
% O in CO₂ (C=12, O=16) is:
% O = (2×16)/44 × 100 = 32/44 × 100 = 72.7%.
A compound is 40% C, 6.7% H, 53.3% O. The empirical formula is:
Mol C=40/12=3.33; H=6.7/1=6.7; O=53.3/16=3.33. Ratio: 1:2:1 → CH₂O.
The empirical formula mass of CH₂O is 30 g/mol. If MW = 180, the molecular formula is:
n = 180/30 = 6. Multiply CH₂O × 6 = C₆H₁₂O₆ (glucose).
How many moles are in 44.0 g of CO₂ (GFM=44.0)?
n = 44.0/44.0 = 1.0 mol.
CuSO₄·5H₂O: how many grams of water per formula unit? (H₂O = 18 g/mol)
5 moles of H₂O × 18 g/mol = 90 g/mol of water.
In stoichiometry, coefficients in the balanced equation represent:
Coefficients represent the mole ratios of substances in the reaction.
N₂ + 3H₂ → 2NH₃. How many moles of NH₃ from 2 mol N₂?
Mole ratio N₂:NH₃ = 1:2. So 2 mol N₂ × (2 mol NH₃/1 mol N₂) = 4 mol NH₃.
The limiting reagent in a reaction is:
Limiting reagent = runs out first → determines theoretical yield.
GFM of Al₂(SO₄)₃ (Al=27, S=32, O=16) is:
2(27) + 3(32 + 4×16) = 54 + 3(96) = 54 + 288 = 342 g/mol.
Theoretical yield = 25 g; actual yield = 20 g. % yield = ?
% yield = 20/25 × 100 = 80%.
The first step in finding empirical formula from percent composition is:
Assume 100 g sample → % becomes grams directly. Then divide each by its molar mass to get moles.
How many liters does 3.0 mol of gas occupy at STP?
3.0 mol × 22.4 L/mol = 67.2 L at STP.
Which formula contains the highest % of nitrogen? (N=14)
% N = (mass N/GFM)×100 for each: NH₃ = 14/17 = 82.4%; N₂H₄ = 28/32 = 87.5%; NO₂ = 14/46 = 30.4%; N₂O = 28/44 = 63.6%. N₂H₄ has the highest percent nitrogen at 87.5%.
If actual yield > theoretical yield, this means:
Actual yield cannot exceed theoretical yield — if it does, there's a measurement or calculation error.
The percent water in CaCl₂·2H₂O (CaCl₂=111, H₂O=18) is:
% water = 2(18)/(111+36) × 100 = 36/147 × 100 = 24.5%.
To find the molecular formula from empirical formula, you need:
n = MW/EFM. You need the actual molecular mass to find n, then multiply subscripts.
GFM of Mg(NO₃)₂ (Mg=24, N=14, O=16) is:
24 + 2(14 + 3×16) = 24 + 2(62) = 24 + 124 = 148 g/mol.
How many grams of H₂O are in 0.50 mol? (GFM=18 g/mol)
g = 0.50 mol × 18 g/mol = 9.0 g.
In 2H₂ + O₂ → 2H₂O, if 4 mol H₂ reacts, how many mol H₂O forms?
Ratio H₂:H₂O = 2:2 = 1:1. So 4 mol H₂ → 4 mol H₂O.
The first step in any mass-to-mass stoichiometry problem is:
Always start by converting grams → moles (÷ GFM). Moles are the universal bridge in stoichiometry.
N₂ + 3H₂ → 2NH₃. How many grams of NH₃ (GFM=17) form from 28 g N₂ (GFM=28)?
28 g N₂ ÷ 28 g/mol = 1 mol N₂ × (2 mol NH₃/1 mol N₂) × 17 g/mol = 34 g NH₃.
In 2H₂ + O₂ → 2H₂O, you have 6 mol H₂ and 2 mol O₂. Which is the limiting reagent?
6 mol H₂ requires 3 mol O₂. Only 2 mol O₂ available → O₂ runs out first → O₂ is limiting.
Using the same reaction above (6 mol H₂, 2 mol O₂, limiting = O₂), how many mol H₂O form?
2 mol O₂ × (2 mol H₂O / 1 mol O₂) = 4 mol H₂O.
How many moles of excess H₂ remain after the reaction above?
O₂ is limiting. 2 mol O₂ uses 2×2 = 4 mol H₂. Started with 6 mol H₂ → 6−4 = 2 mol H₂ left over.
Theoretical yield is 50.0 g but only 38.0 g is collected. % yield = ?
% yield = 38.0/50.0 × 100 = 76%.
At STP, how many liters does 3.5 mol CO₂ occupy?
3.5 mol × 22.4 L/mol = 78.4 L at STP.
In N₂ + 3H₂ → 2NH₃, what is the mole ratio of H₂ to NH₃?
Coefficient of H₂ = 3; coefficient of NH₃ = 2 → ratio H₂:NH₃ = 3:2.
How many molecules are in 4.0 g of H₂ (GFM = 2.0)?
4.0 g ÷ 2.0 g/mol = 2.0 mol × 6.02×10²³ = 1.20×10²⁴ molecules.
Which statement about excess reagent is correct?
The excess reagent is NOT completely consumed — some remains after the limiting reagent runs out.
2Al + 3Cl₂ → 2AlCl₃. How many grams of AlCl₃ (GFM=133.5) form from 27 g Al (GFM=27)?
27 g Al ÷ 27 g/mol = 1 mol Al × (2 mol AlCl₃/2 mol Al) × 133.5 g/mol = 133.5 g.
Given: CH₄ + 2O₂ → 2H₂O + CO₂ + energy. 12 g CH₄ and 48 g O₂ react to produce 33 g CO₂. How many grams of H₂O are produced?
Conservation of mass: total reactants = 12+48 = 60 g. Total products = 33 g CO₂ + x g H₂O = 60 g → x = 27 g H₂O.
What is the gram-formula mass of P₂O₅? (P=31, O=16)
GFM = 2(31) + 5(16) = 62 + 80 = 142 g/mol.
What is the percent composition by mass of Cu in CuSO₄? (GFM = 160 g/mol, Cu = 64)
% Cu = (64/160) × 100 = 40%.
N₂ + 3H₂ → 2NH₃. How many moles of H₂ are needed to produce 10.0 mol NH₃?
Mole ratio H₂:NH₃ = 3:2. 10.0 mol NH₃ × (3 mol H₂/2 mol NH₃) = 15.0 mol H₂.
What is the gram-formula mass of Fe(NO₃)₃? (Fe=56, N=14, O=16)
Fe(NO₃)₃ = 56 + 3(14 + 3×16) = 56 + 3(62) = 56 + 186 = 242 g/mol.
What is the mass in grams of 2.0 moles of NO₂? (N=14, O=16)
GFM of NO₂ = 14 + 2(16) = 46 g/mol. 2.0 mol × 46 g/mol = 92 g.
What is the mass of 1.5 moles of CO₂? (C=12, O=16)
GFM of CO₂ = 12 + 2(16) = 44 g/mol. 1.5 × 44 = 66 g.
A compound has a molecular mass of 54 and an empirical formula of CH (mass = 13). What is the molecular formula?
n = 54/13 ≈ 4.15 → round to 4. Molecular formula = (CH)₄ = C₄H₄.
Which type of reaction is: 2H₂ + O₂ → 2H₂O?
Two reactants combine to form one product → synthesis (combination) reaction.
The reaction Zn + CuSO₄ → ZnSO₄ + Cu is best classified as a
One element (Zn) displaces another element (Cu) from a compound → single replacement reaction.
In balancing equations, you can change only the
Only coefficients can be changed — changing subscripts would change the identity of the substance.
Fe + ZnSO₄ → ? (use Table J)
Zn is ABOVE Fe on Table J (zinc is more active than iron) → Fe cannot displace Zn from solution → No reaction (NR).
Cu + FeSO₄ → ? (use Table J)
Cu is BELOW Fe on Table J → Cu cannot displace Fe → NR.
The balanced equation for: H₂ + N₂ → NH₃ is:
3H₂ + N₂ → 2NH₃. Check: 6H and 2N on each side. ✓
Which pair would produce a precipitate? (Table F: AgCl is insoluble)
AgNO₃ + NaCl → AgCl↓ + NaNO₃. AgCl is insoluble → precipitate forms.
Combustion of C₃H₈ (propane) produces:
Complete combustion of hydrocarbons always produces CO₂ and H₂O.
Which type of reaction is: CaCO₃ → CaO + CO₂?
One compound breaks into two simpler substances → decomposition.
Spectator ions are:
Spectator ions don't participate in the reaction — they're present but unchanged on both sides.
The net ionic equation for Pb(NO₃)₂ + 2KI → PbI₂↓ + 2KNO₃ is:
K⁺ and NO₃⁻ are spectators. Only Pb²⁺ and I⁻ react to form the insoluble precipitate.
F₂ + 2KBr → 2KF + Br₂. F₂ displaces Br because:
Table J halogens: F > Cl > Br > I. F is highest → displaces Br.
Which is a double replacement reaction?
AgNO₃ + NaCl → AgCl + NaNO₃: ions from two compounds switch partners → double replacement.
Table F is used to predict:
Table F lists solubility rules — used to predict precipitates in double replacement reactions.
A balanced chemical equation demonstrates the law of:
Balancing equations ensures the same number of each atom on both sides → conservation of mass.
Diatomic elements include:
The 7 diatomic elements: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂. Always write with subscript 2 when uncombined.
Which is an example of a synthesis reaction?
SO₂ + H₂O → H₂SO₃: two reactants combine to form one product → synthesis.
In a neutralization reaction between HNO₃ and KOH, the salt produced is:
Acid anion (NO₃⁻) + base cation (K⁺) → KNO₃ (potassium nitrate).
What are the correct coefficients to balance: Al + O₂ → Al₂O₃?
4Al + 3O₂ → 2Al₂O₃. Check: 4 Al and 6 O on each side. ✓
Which statement about single replacement reactions is true?
Table J: single replacement is spontaneous only when the replacing element is HIGHER (more active) on the list.
Given: Ba(NO₃)₂(aq) + Na₂SO₄(aq) → 2NaNO₃(aq) + BaSO₄(s). What type of reaction is shown?
Two ionic compounds exchange partners (Ba²⁺ pairs with SO₄²⁻; Na⁺ pairs with NO₃⁻) → double replacement. BaSO₄ precipitates.
Which equation represents a single replacement reaction?
Al replaces H in HCl → single replacement. Al + HCl: one element displaces another from a compound.
Based on Table J, which element will replace Pb from Pb(NO₃)₂(aq)?
Table J activity series: Mg is more active than Pb (higher on the list) → Mg spontaneously replaces Pb. Cu, Ag, and Au are below Pb → cannot replace it.
During a phase change (e.g., melting), temperature:
At a phase change, energy goes into or out of the system as potential energy (breaking/forming intermolecular attractions). KE (temperature) stays constant.
Which formula is used during the sloped section of a heating curve?
Sloped section = temperature is changing → q = mCΔT.
The specific heat of water is 4.18 J/g·K. How much heat to raise 10.0 g from 20°C to 30°C?
q = mCΔT = 10.0 × 4.18 × 10 = 418 J.
The flat section at the boiling point on a heating curve uses:
Flat at BP = liquid→gas phase change → q = mH_v (heat of vaporization).
London dispersion forces increase with increasing:
Larger molecules have more electrons → stronger temporary dipoles → stronger LDFs.
Which substance has the strongest intermolecular forces?
HF has H bonded directly to F → hydrogen bonding → strongest IMFs among these.
The conversion to Kelvin is required before using gas law formulas because
Gas laws require an absolute temperature scale. At 0 K, KE = 0. Using Celsius (which can be 0 or negative) would give nonsensical results.
Which substance has the lowest boiling point, indicating weakest IMFs?
CH₄ is nonpolar with only weak LDFs → lowest BP among these.
At what region of the heating curve does PE increase while KE stays constant?
At flat sections (phase changes): energy goes into overcoming IMFs (PE ↑), not increasing motion (KE/T constant).
A substance has a high vapor pressure. This indicates:
High VP = molecules escape easily = weak IMFs. Lower IMFs → lower BP and higher VP.
Ice melts at 0°C. The heat absorbed during melting is calculated by:
Melting = solid→liquid phase change → flat on heating curve → q = mH_f.
Which is a GAS at room temperature (25°C)?
Nitrogen boils at −196°C → is a gas at room temperature (25°C > −196°C).
Temperature is a measure of:
Temperature measures the AVERAGE KE of particles — not total (which would depend on sample size).
As water evaporates, the remaining water becomes:
High-energy molecules escape (evaporate) → average KE of remaining molecules decreases → cooling effect.
Which state of matter has a definite volume but no definite shape?
Liquids have definite volume (incompressible) but take the shape of their container.
The boiling point of a liquid is the temperature where:
Boiling occurs when vapor pressure = atmospheric pressure. The 'normal' BP is at 101.3 kPa.
H₂O has an unusually high boiling point for its molecular mass because:
H₂O molecules form H-bonds (H bonded to O) — much stronger than the LDFs of similar-size molecules.
On Table H, which substance has the highest vapor pressure at 50°C?
Lower BP = weaker IMFs = higher VP. On Table H, the curve highest on the y-axis at any given T has highest VP.
During the cooling curve, the flat section at the freezing point represents:
Freezing = liquid→solid: IMFs form, PE decreases, energy is released to surroundings. T stays constant.
The heat of vaporization of water is 2260 J/g. How much heat to boil 5.0 g of water at 100°C?
q = mH_v = 5.0 g × 2260 J/g = 11300 J.
Which process requires the most energy?
H_v (2260 J/g) >> H_f (334 J/g) >> heating through 100°C (418 J). Vaporization requires the most energy.
Substances with strong IMFs tend to have:
Strong IMFs → harder to separate molecules → higher BP and lower VP (less evaporation tendency).
What type of particles are found in a plasma?
Plasma is a high-energy ionized gas consisting of free electrons and positive ions.
During condensation (gas → liquid), energy is:
Condensation = gas→liquid: IMFs form (exothermic) → energy released. This is the reverse of vaporization.
In the heating curve, all five regions in order are:
Solid heating → flat (melting) → liquid heating → flat (boiling) → gas heating. These are the 5 segments.
What happens to the potential energy of water molecules as water evaporates from a wet surface?
Evaporating molecules overcome intermolecular attractions → PE increases as they escape the liquid surface. This is why evaporation is endothermic and cools the surface.
A student left one paper towel dry in an evaporation experiment. In terms of experimental design, why?
The dry towel is the control group — it shows what temperature change (if any) occurs WITHOUT evaporation, so results can be compared fairly.
Heat flows between two objects in contact. In which direction does heat flow?
Heat always flows from higher temperature (more average KE) to lower temperature — this is the second law of thermodynamics.
At standard pressure, which 5.0-gram sample of xenon has the greatest entropy?
Gas state = greatest disorder = highest entropy. Among gas samples, Xe(g) at 165 K has the most disordered particles.
Which physical changes are endothermic (absorb energy)?
Endothermic phase changes require energy input: melting (solid→liquid) and evaporating/vaporizing (liquid→gas). Condensation and freezing release energy (exothermic).
On a heating curve, segment CD (boiling plateau) is longer than segment AB (melting plateau) because
H_v (2260 J/g for water) >> H_f (334 J/g). More energy is required to vaporize than to melt → the boiling plateau takes longer at the same constant heating rate.
What is the minimum heat required to completely melt 200. grams of H₂O(s) at its melting point? (H_f = 334 J/g)
q = mH_f = 200. g × 334 J/g = 66,800 J.
When an ice cube is placed in 100 mL of water at 25°C, which describes the heat transfer?
Heat flows from hot to cold. The warmer water loses heat energy to the colder ice. The ice gains heat and melts; the water cools.
At STP, a 12.0-liter sample of CH₄(g) has the same total number of molecules as
Avogadro's Law: equal volumes of gas at the same T and P contain equal numbers of molecules. 12.0 L CH₄ = 12.0 L CO₂ (both at STP).
A gas at 2 atm and 4 L is compressed to 1 L at constant T. New pressure?
Boyle's Law: P₁V₁=P₂V₂ → 2×4 = P₂×1 → P₂ = 8 atm.
A gas at 300 K occupies 6 L. At 600 K (constant P), it occupies:
Charles's Law: V₁/T₁=V₂/T₂ → 6/300 = V₂/600 → V₂ = 12 L.
25°C in Kelvin is:
K = °C + 273 = 25 + 273 = 298 K.
Gases deviate most from ideal behavior under:
Low T (molecules slow, attractions matter) + high P (molecules compressed close together) → most deviation from ideal.
At STP, 2 mol of any gas occupies:
1 mol = 22.4 L at STP, so 2 mol = 2 × 22.4 = 44.8 L.
According to the kinetic molecular theory, which assumption is made about ideal gas molecules?
Zero IMF is an ideal gas ASSUMPTION. Real gases have some IMFs — this is why they deviate from ideal behavior.
If pressure of a gas increases at constant volume, temperature:
Gay-Lussac's Law: P∝T at constant V. Higher pressure → higher temperature.
A gas at 1 atm and 546 K is cooled to 273 K at constant V. New pressure?
Gay-Lussac's: P₁/T₁=P₂/T₂ → 1/546=P₂/273 → P₂=0.5 atm.
Which gas behaves most like an ideal gas?
He: smallest atom, monatomic, nonpolar, very weak LDFs → closest to ideal gas behavior.
Boyle's Law applies at constant:
Boyle's Law: P₁V₁=P₂V₂ at constant TEMPERATURE (and constant n).
Equal volumes of H₂ and O₂ at the same T and P contain:
Avogadro's Law: equal volumes at same T and P contain equal numbers of molecules (regardless of mass).
The units of pressure in Table A (STP) are:
Table A: STP = 101.3 kPa = 1 atm = 760 mmHg = 760 torr.
Combined gas law: P₁=2 atm, V₁=5 L, T₁=300 K, T₂=600 K, P₂=4 atm. V₂=?
P₁V₁/T₁=P₂V₂/T₂ → (2×5)/300=(4×V₂)/600 → 10/300=4V₂/600 → V₂=5 L.
According to KMT, all gas molecules at the same temperature have:
KMT: average KE depends only on temperature. All gases at same T have same average KE (not same speed — lighter molecules move faster).
Dalton's Law of Partial Pressures states:
Each gas in a mixture exerts pressure independently; total = sum of all partial pressures.
At absolute zero (0 K), according to theory:
0 K = absolute zero: theoretically all particle motion (KE) = 0. Cannot actually be achieved.
P₁=3 atm, V₁=2 L, T₁=273 K, P₂=1 atm, T₂=546 K. V₂=?
P₁V₁/T₁=P₂V₂/T₂ → (3×2)/273=(1×V₂)/546 → 6/273=V₂/546 → V₂=12 L.
Which correctly states Charles's Law?
Charles's Law: volume and temperature (Kelvin) are directly proportional at constant pressure.
Standard temperature for STP is:
STP = 0°C (273 K) and 101.3 kPa. (Note: IUPAC changed this to 0°C/100 kPa in 1982, but this course still uses 273 K/101.3 kPa from Table A.)
Which gas behaves most like an ideal gas, and why?
NH₃ has strong H-bonding (H to N) → significant IMFs → large deviation from ideal. H₂ has negligible IMFs.
A 320-mL sample of N₂ is at 300 K and 100 kPa. The temperature changes to 450 K and pressure to 60.0 kPa. What is the new volume?
Combined gas law: V₂ = P₁V₁T₂/(T₁P₂) = (100×320×450)/(300×60.0) = 14,400,000/18,000 = 800 mL.
At 300 K, gas particles collide with a certain force. How does the force of collisions change at 450 K?
Higher temperature → higher average KE → particles move faster → collide with greater force.
Which change causes a real gas to behave more like an ideal gas?
Ideal behavior: high T (fast-moving, less interaction) + low P (far apart, less volume). Increasing T and decreasing P pushes toward ideal conditions.
A nitrogen gas sample is in a sealed rigid cylinder (constant volume). How many significant figures are in the temperature '300. K'?
300. K — the decimal point makes all three digits significant → 3 sig figs.
A gas sample has P = 240 kPa, V = 70.0 mL, T = 300 K. When T = 150 K and P = 160 kPa, what is the new volume?
V₂ = P₁V₁T₂/(T₁P₂) = (240×70.0×150)/(300×160) = 2,520,000/48,000 = 52.5 mL.
A rigid cylinder contains a gas at STP. The gas is heated to 410 K. What is the new pressure?
Gay-Lussac's Law: P₁/T₁ = P₂/T₂ → P₂ = P₁T₂/T₁ = 1.0 × 410/273 = 1.50 atm ≈ 1.5 atm.
A gas is heated from 293 K to 303 K at constant pressure of 1.0 atm. Original volume is 6.0 L. New volume is
Charles's Law: V₂ = V₁T₂/T₁ = 6.0 × 303/293 = 6.2 L.
Which graph correctly shows the relationship between pressure and Kelvin temperature for an ideal gas at constant volume?
Gay-Lussac's Law: P ∝ T (Kelvin) at constant volume → straight line through the origin (direct proportion).
A solution is below the solubility curve. It is:
Below the curve = unsaturated: more solute can still dissolve at that temperature.
How does increasing temperature affect the solubility of CO₂ gas?
Gas solubility DECREASES with increasing temperature (molecules gain enough energy to escape the solvent). This is why warm soda goes flat.
The molarity of a solution with 0.50 mol NaCl in 250 mL solution is:
M = mol/L = 0.50 mol / 0.250 L = 2.0 M.
The statement 'like dissolves like' means that
Polar/ionic solutes dissolve in polar solvents (water). Nonpolar solutes dissolve in nonpolar solvents (hexane, oil).
Stirring a solution increases the rate of dissolving because:
Stirring moves saturated solution away from the solute surface and brings fresh solvent into contact — only increases RATE, not total solubility.
Which colligative property explains why salt lowers the freezing point of water on roads?
Dissolving NaCl in water lowers the freezing point (FP depression) — prevents ice formation.
An electrolyte solution conducts electricity because:
Ions in solution are free to move and carry electrical current → electrolytic conduction.
A supersaturated solution is:
Supersaturated = above the solubility curve = more dissolved than maximum → unstable → excess crystallizes out.
Henry's Law states that as pressure increases, gas solubility:
Henry's Law: S = kP. Higher pressure → more gas molecules forced into solution → greater solubility.
If 500 mL of 2.0 M NaCl is diluted to 2.0 L, the new molarity is:
M₁V₁=M₂V₂ → 2.0×0.500=M₂×2.0 → M₂=0.50 M.
Which has a greater effect on boiling point elevation — 1 mol NaCl or 1 mol sugar dissolved in water?
1 mol NaCl → 2 mol particles (Na⁺ + Cl⁻). Colligative properties depend on particle COUNT → NaCl has greater effect.
A saturated solution is best described as:
Saturated means at maximum capacity for that temperature — on the solubility curve line.
What does ppm measure?
ppm = (mass solute / mass solution) × 10⁶. Used for very dilute concentrations (water quality, etc.).
Which factor affects both the rate of dissolving and the equilibrium amount (solubility)?
Temperature affects solubility (the equilibrium position). Stirring and crushing only affect rate, not the final amount.
At 40°C, KNO₃ solubility is about 65 g/100 g H₂O (from Table G). If 50 g is dissolved at 40°C, the solution is:
50 g < 65 g maximum → below the curve → unsaturated.
Water is called the universal solvent because:
Water's polarity and H-bonding ability allow it to dissolve many polar and ionic compounds. Not literally universal — nonpolar substances don't dissolve well.
During osmosis, water moves through a semipermeable membrane from a region of
Osmosis: water moves from low solute concentration (high water concentration) to high solute concentration (low water concentration).
What is the concentration of a solution made by dissolving 117 g of NaCl (GFM=58.5) in 2.0 L?
mol NaCl = 117/58.5 = 2.0 mol. M = 2.0/2.0 = 1.0 M.
A nonelectrolyte in water:
Nonelectrolytes (sugar, ethanol) dissolve but don't produce ions → no electrical conductivity.
Which solution has the lowest freezing point?
CaCl₂ → Ca²⁺ + 2Cl⁻ = 3 mol particles (most particles) → greatest FP depression.
Crystallization occurs when a solution becomes:
Crystallization is triggered when a solution becomes supersaturated — more solute is dissolved than the solvent can hold at that temperature.
A hot saturated KNO₃ solution is slowly cooled. What happens?
Cooling lowers solubility → solution goes above the curve (supersaturated) → excess KNO₃ crystallizes out.
KNO₃ solubility is 110 g/100 g H₂O at 60°C and 32 g at 20°C. How much crystallizes when cooled from 60°C to 20°C (starting with a saturated solution at 60°C)?
Amount that crystallizes = 110 − 32 = 78 g per 100 g H₂O.
A seed crystal is added to a supersaturated solution. It will:
A seed crystal provides a surface (nucleation site) for solute molecules to begin crystallizing onto.
When a dissolved solute crystallizes out of solution, this process is classified as a
Crystallization is a physical change — the solute changes from dissolved to solid form, but its chemical identity is unchanged.
Which substance is best purified by fractional crystallization from Table G?
KNO₃ has a steeply rising solubility curve → large difference between hot and cold solubility → crystallizes out easily and in large amounts on cooling.
What is the primary driving force for crystallization when a solution is cooled?
Solubility of most solids decreases as temperature falls → what was dissolved now exceeds capacity → crystallizes.
After crystallization, the crystals are separated from the remaining solution (mother liquor) by:
Filtration separates the solid crystals from the liquid mother liquor — the crystals are too large to pass through filter paper.
According to Table G, how many grams of KNO₃ are needed to saturate 200 grams of water at 70°C?
Table G: KNO₃ solubility at 70°C is about 134 g per 100 g H₂O. Since we have 200 g of water (double the reference amount), we need double the solute: 134 × 2 = 268 g.
A flask of water with solid KCl visible at the bottom is sealed. The solid KCl does not dissolve further. The solution is best described as
Solid present with no more dissolving = saturated. The system is at equilibrium: dissolving rate = crystallizing rate.
Why is potassium nitrate classified as an electrolyte?
Electrolytes release ions when dissolved in water → solution conducts electricity. KNO₃ dissociates: K⁺ + NO₃⁻.
Compared to pure water, a solution of CaCl₂ in water at standard pressure has
Colligative properties: any dissolved solute raises BP and lowers FP. CaCl₂ → 3 particles → larger effect.
Which compound is an electrolyte?
H₃PO₄ is an acid that ionizes in water → electrolyte. C₂H₆ (ethane) and CH₃OH (methanol) are nonelectrolytes. Pure H₂O is a very weak electrolyte.
ΔH = +85 kJ. This reaction is:
Positive ΔH = energy absorbed = endothermic.
In an endothermic reaction, the surroundings feel:
Endothermic absorbs heat from surroundings → surroundings lose energy → surroundings feel cold.
A catalyst affects a PE diagram by:
A catalyst lowers Ea for BOTH forward and reverse reactions. ΔH (difference between reactant and product PE) does NOT change.
Activation energy is measured from:
Ea (forward) = peak height ABOVE reactants level. This is the energy needed to reach the activated complex.
If bonds broken require 400 kJ and bonds formed release 550 kJ, ΔH is:
ΔH = bonds broken − bonds formed = 400 − 550 = −150 kJ → exothermic (formed > broken).
In an exothermic PE diagram, the products are positioned:
Exothermic: energy is released → products end at LOWER PE than reactants.
Heat is treated as a reactant in which type of reaction?
Endothermic: heat is absorbed → write heat on the reactant side (as if it's a substance being consumed).
Entropy increases when:
Dissolving spreads particles throughout solution → more disorder → increased entropy.
Combustion of methane (CH₄ + 2O₂ → CO₂ + 2H₂O) is:
Combustion is always exothermic (releases heat) → ΔH is negative.
On a PE diagram, the activated complex is located:
The activated complex (transition state) is at the maximum energy point — the peak of the PE curve.
For a reaction where ΔH = −200 kJ, which statement correctly describes the potential energy?
ΔH = PE_products − PE_reactants = −200 kJ → products are 200 kJ lower in PE than reactants → exothermic.
Which process results in a decrease in entropy?
Freezing: liquid → solid = less disorder → decreased entropy (ΔS < 0).
The reverse activation energy (Ea reverse) is measured from:
Ea(reverse) = energy needed to go from products back to the activated complex = peak height above products.
Photosynthesis (6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂) is:
Photosynthesis absorbs light energy to build glucose → endothermic, +ΔH.
A catalyst speeds up a reaction by:
A catalyst provides an alternate reaction pathway with lower Ea → more collisions have sufficient energy → faster rate.
In an exothermic reaction at equilibrium, heat is treated as a:
Exothermic: heat is released → heat appears as a PRODUCT in the reaction equation.
The Gibbs free energy equation is ΔG = ΔH − TΔS. A reaction is spontaneous when:
ΔG < 0 (negative Gibbs free energy) indicates a spontaneous reaction under the given conditions.
Which statement correctly describes the breaking of the O=O bond in O₂?
Breaking bonds always requires energy input → endothermic. Only forming bonds releases energy.
For a reaction: ΔH = +50 kJ. At higher temperature, Le Chatelier predicts equilibrium shifts:
Endothermic (+ΔH): heat is a reactant. Adding heat (raising T) shifts toward products (right).
Which correctly describes Hess's Law?
Hess's Law: overall ΔH = sum of ΔH values for each step. ΔH is a state function — path-independent.
Based on Table I, which compound produces an exothermic process when dissolved in water at 298 K?
NaOH dissolving has a negative ΔH in Table I → exothermic (solution warms). The others have positive ΔH → endothermic.
Systems in nature tend to undergo changes that result in:
Nature favors: lower potential energy (exothermic) AND greater disorder (higher entropy). ΔG = ΔH − TΔS → spontaneous when ΔG < 0.
The heat of reaction equals PE of products minus PE of reactants. If this value is negative:
ΔH = PE_products − PE_reactants. Negative value → products are lower in energy than reactants → energy released → exothermic.
What is the heat required to completely vaporize 12.5 g of H₂O at 100°C? (H_v = 2260 J/g)
q = mH_v = 12.5 g × 2260 J/g = 28,250 J ≈ 28,300 J. Use H_v because it's a phase change (flat section).
In the equation Cu + S → CuS + energy, why is the energy term written to the right of the arrow?
Forming bonds releases energy (exothermic). Energy appears as a product when bond formation releases it → written on the product side.
Which change is exothermic (releases energy)?
Freezing = liquid→solid: IMFs form, PE decreases, energy released to surroundings → exothermic. Sublimation, melting, and vaporization all absorb energy (endothermic).
Salt A is dissolved in water and the solution temperature decreases. Salt B is dissolved and temperature increases. Which conclusion is correct?
Solution cooling = heat absorbed from surroundings = endothermic (Salt A). Solution warming = heat released = exothermic (Salt B).
Which change results in an increase in disorder (entropy)?
Solid → gas (sublimation) greatly increases disorder → entropy increases. All other options go from more to less disordered states.
At equilibrium, the forward and reverse rates are:
Chemical equilibrium: forward rate = reverse rate. Both reactions continue but at equal speeds.
Which change does not affect the equilibrium position?
A catalyst speeds attainment of equilibrium but does NOT change the equilibrium position (concentrations at equilibrium).
For N₂ + 3H₂ ⇌ 2NH₃ + heat, increasing temperature shifts equilibrium:
Heat is a product (exothermic). Adding heat = adding product → system shifts LEFT to relieve stress.
Collision theory states that which three conditions must be met for a reaction to occur?
All three required: (1) collision, (2) proper orientation, (3) energy ≥ Ea. Missing any = no reaction.
Removing a product from an equilibrium mixture shifts it:
Removing product = stress on product side → system shifts RIGHT to replace it (toward products).
For the reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), increasing pressure shifts equilibrium:
Higher pressure → shift toward fewer moles of gas. Left side has 4 mol gas, right has 2 → shifts RIGHT.
Which statement best describes a system at dynamic equilibrium?
Dynamic = still occurring in both directions at equal rates. Not static — concentrations stay constant but both reactions continue.
Increasing surface area of a solid reactant affects:
Greater surface area = more exposed particles = faster rate. Doesn't change Keq or equilibrium concentrations.
Which factor increases reaction rate AND shifts equilibrium for an endothermic reaction?
Temperature increase: speeds reaction (rate ↑) AND shifts equilibrium toward products for an endothermic reaction (heat is reactant).
For an exothermic reaction at equilibrium, adding more reactant shifts equilibrium:
Adding reactant = stress on reactant side → system shifts AWAY from it (right), toward products.
Keq = [C]²[D] / [A][B]³ is the expression for: aA + bB ⇌ cC + dD. What are a, b, c, d?
Keq = [products]^coefficients / [reactants]^coefficients. So a=1 (A¹), b=3 (B³), c=2 (C²), d=1 (D¹).
An inert gas added to a sealed container at constant volume:
Inert gas at constant volume doesn't change partial pressures of reactants/products → no equilibrium shift.
Ionic reactions in aqueous solution are generally faster than molecular reactions because:
Ions in solution interact immediately through electrostatic attraction — no covalent bonds to break first.
Which is true of a catalyst in an equilibrium system?
A catalyst lowers Ea equally for forward and reverse → reaches equilibrium faster → same equilibrium position and same Keq.
For CO(g) + 3H₂(g) ⇌ CH₄(g) + H₂O(g), decreasing pressure shifts equilibrium:
Left side: 4 mol gas. Right side: 2 mol gas. Decrease pressure → shift toward MORE moles → LEFT.
The equilibrium expression excludes:
Keq excludes pure solids and pure liquids — their concentrations don't change and are incorporated into the constant.
Which correctly explains why crushing a solid increases reaction rate?
Smaller particles = greater surface area = more surface molecules available to collide with reactant → faster rate.
At equilibrium, concentrations of reactants and products are:
At equilibrium: concentrations remain CONSTANT over time, but they're not necessarily equal to each other.
Which factor will shift the position of a chemical equilibrium?
Temperature change alters the rate of both reactions differently (activating Arrhenius dependence) → equilibrium position shifts.
If concentration of product is increased, Keq:
Keq is a constant at a given temperature — it doesn't change when concentrations change. The system just shifts to re-establish the same ratio.
A sealed 100-mL flask contains 50 g of water at 25°C. Which term best describes this system?
Sealed flask with liquid water: evaporation rate = condensation rate → liquid-vapor physical equilibrium. No chemical reaction occurs.
On a concentration-vs-time graph, equilibrium is established at the point where:
Equilibrium = no further net change in concentrations → all curves level off and stay flat. Rates are equal (not zero), concentrations are constant (not necessarily equal).
Given: H₂(g) + I₂(g) + energy ⇌ 2HI(g). When the temperature is increased, the equilibrium shifts to the
Heat is a reactant (endothermic — energy on the left). Adding heat → shift RIGHT (toward products) → more HI forms → HI concentration increases.
In the reaction Fe(s) + HCl(aq), which conditions produce the fastest rate?
Fastest rate: maximum surface area (powder) + maximum temperature (303 K). Both factors increase collision frequency and energy.
Hydrochloric acid reacts faster with powdered zinc than with an equal mass of zinc strips because powdered zinc has
Crushing/powdering increases surface area → more Zn atoms exposed to HCl → more frequent collisions → faster reaction rate.
A catalyst increases the rate of a reaction by
A catalyst provides an alternate reaction pathway with a LOWER activation energy → more collisions have sufficient energy → faster rate.
Increasing the temperature of a reaction increases the rate by
Higher temperature → faster-moving particles → more frequent collisions AND more collisions with energy ≥ Ea → increased rate.
A chemical reaction between iron atoms and oxygen molecules can only occur if
Collision theory: reactions require collisions with proper orientation AND sufficient energy. Not all reactions need heating or a catalyst.
[H⁺] = 1×10⁻⁵ M. The pH is:
pH = −log[H⁺] = −log(10⁻⁵) = 5.
A solution has pH = 9. It is:
pH > 7 = basic.
pOH of a solution with pH = 3 is:
pH + pOH = 14 → pOH = 14 − 3 = 11.
Which substance is classified as a strong acid?
HNO₃ is one of the 6 strong acids (HCl, HBr, HI, HNO₃, H₂SO₄, HClO₄). The others listed are weak acids.
An Arrhenius base in water releases:
Arrhenius base releases hydroxide ions (OH⁻) in aqueous solution.
A Brønsted-Lowry acid is defined as a proton:
Brønsted-Lowry acid donates an H⁺ (proton) to a base.
Acid + base → ??? + water
Neutralization: acid + base → salt + water. The salt contains the cation from the base and anion from the acid.
In a titration, 25.0 mL of 0.40 M HCl neutralizes a NaOH solution. If 50.0 mL of NaOH was used, its molarity is:
M_A×V_A = M_B×V_B → 0.40×25.0 = M_B×50.0 → M_B = 10/50 = 0.20 M.
The indicator phenolphthalein is colorless in acid and pink in base. At pH = 5, it is:
Phenolphthalein is colorless in acid (pH < 8.2) and pink in base. pH 5 is acidic → colorless.
How much more acidic is a solution at pH 2 compared to pH 4?
pH is logarithmic: difference of 2 pH units = 10² = 100× difference in [H⁺].
The Kw of water at 25°C is:
Kw = [H⁺][OH⁻] = 1×10⁻¹⁴ at 25°C. In pure water: [H⁺] = [OH⁻] = 1×10⁻⁷.
Which substance can act as both an acid and a base (amphoteric)?
Water is amphoteric: can donate H⁺ (act as acid) or accept H⁺ (act as base). Also: HCO₃⁻.
A weak acid in water:
Weak acids only partially ionize — an equilibrium is established between the acid and its ions.
Litmus is red in acid and blue in base. A litmus paper turns RED in an unknown solution. The solution is:
Litmus turns red in acid (pH < 7).
The conjugate base of H₂CO₃ is:
Conjugate base = acid minus one H⁺. H₂CO₃ − H⁺ = HCO₃⁻ (bicarbonate).
[OH⁻] in a solution with pH = 11 is:
pOH = 14 − 11 = 3. [OH⁻] = 10⁻³ = 1×10⁻³ M.
When HCl dissolves in water, it produces:
HCl is a strong acid: HCl → H⁺ + Cl⁻. The H⁺ combines with water to form H₃O⁺.
In a neutralization reaction, the salt that forms contains
Salt = anion from the acid + cation from the base. HCl + NaOH → NaCl: Cl⁻ (from acid) + Na⁺ (from base).
A solution with [H⁺] = 1×10⁻⁷ M is:
pH = −log(10⁻⁷) = 7. pH = 7 = neutral.
In a 1:1 titration, the equivalence point is reached when:
Equivalence point: mol H⁺ = mol OH⁻ (complete neutralization). For HCl + NaOH, this happens at pH 7, but not always (depends on acid/base strengths).
When pH changes from 4.0 to 7.0, what happens to the concentration of hydronium ions?
pH increases by 3 units → [H⁺] decreases by 10³ = 1000. pH 4 to pH 7 = 1000× less acidic.
NH₃ + H₂O ⇌ NH₄⁺ + OH⁻. In the reverse reaction, which species donates an H⁺ ion?
In the reverse reaction, NH₄⁺ → NH₃ + H⁺ (donates a proton) → NH₄⁺ is the Brønsted-Lowry acid in the reverse direction.
What color is methyl orange indicator in a basic solution (e.g., NaOH)?
Methyl orange: red in acid (pH < 3.1), yellow in base (pH > 4.4). NaOH is strongly basic → methyl orange is YELLOW.
15.0 mL of HCl(aq) is neutralized by 25.2 mL of 0.50 M NaOH. What is the molarity of the HCl?
M_A × V_A = M_B × V_B → M_A × 15.0 = 0.50 × 25.2 → M_A = 12.6/15.0 = 0.84 M.
In the reversible reaction CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺, the two species that can donate an H⁺ in the equation are
In the forward reaction: CH₃COOH donates H⁺. In the reverse reaction: H₃O⁺ donates H⁺ back. These two are both H⁺ donors (Brønsted-Lowry acids) in the overall equation.
Which solution is the best conductor of electric current?
More dissolved ions → better conductivity. 0.1 mol NaCl provides the most ions (0.1 mol Na⁺ + 0.1 mol Cl⁻) → best conductor.
Phenolphthalein indicator is pink in an aqueous solution with a pH of
Phenolphthalein is colorless at pH < 8.2 and pink at pH > 10. pH = 12 is strongly basic → pink/fuchsia.
What is the color of bromcresol green indicator in a solution with a pH of 2.0?
Table M: Bromcresol green is yellow in acid (pH < 3.8) and blue in base (pH > 5.4). pH 2.0 is acidic → yellow.
Compared to a 1.0-liter solution at pH 7.0, a 1.0-liter solution at pH 5.0 contains
pH 5.0 vs pH 7.0: difference of 2 units → [H⁺] differs by 10² = 100×. pH 5 has 100× more H⁺ than pH 7.
In the mnemonic OIL RIG, 'RIG' means:
OIL RIG: Oxidation Is Loss, Reduction Is Gain of electrons.
The oxidation number of Cr in Cr₂O₃ is:
O = −2 (×3 = −6 per Cr). For neutral compound: 2(Cr) + (−6) = 0 → 2Cr = +6 → Cr = +3.
In Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag, copper is:
Cu → Cu²⁺: loses 2 electrons → oxidized. Cu is the REDUCING agent (it donates electrons to reduce Ag⁺).
In a voltaic cell, the electron flow in the external circuit is from:
Electrons are produced at the anode (oxidation) and flow through external wire to cathode (reduction).
Which half-reaction represents a reduction?
Fe³⁺ + e⁻ → Fe²⁺: electrons GAINED by Fe³⁺ → reduction.
What is the oxidation number of S in H₂SO₄?
H=+1(×2=+2), O=−2(×4=−8). Sum=0 → +2 + S − 8 = 0 → S = +6.
An electrolytic cell is used for:
Electrolytic cells use external electrical energy to drive nonspontaneous reactions (electroplating, electrolysis of water).
In ANY electrochemical cell, oxidation always occurs at the
Oxidation ALWAYS at the anode — regardless of cell type. (Anode starts with vowel, as does Oxidation.)
What is the oxidation state of Mn in MnO₄⁻ (permanganate)?
O=−2(×4=−8). Ion charge=−1. Mn + (−8) = −1 → Mn = +7.
A reducing agent:
Reducing agent: loses electrons (is itself OXIDIZED) → causes another substance to be reduced.
In the half-reaction Zn²⁺ + 2e⁻ → Zn, electrons appear as reactants. This half-reaction represents
Electrons as reactants (on the left) = electrons being GAINED = reduction.
The salt bridge in a voltaic cell allows:
Salt bridge: ions (not electrons) flow through it to maintain charge balance in each half-cell.
To balance a redox equation, the number of electrons lost must equal:
In any redox reaction: e⁻ lost by reducing agent = e⁻ gained by oxidizing agent. Charge must be conserved.
What is the oxidation number of Fe in Fe₂O₃?
O=−2(×3=−6). For neutral: 2Fe + (−6) = 0 → 2Fe = +6 → Fe = +3.
Table J (activity series) is used to determine whether:
Table J: a single replacement reaction is spontaneous if the replacing element is HIGHER (more active) on the list.
In a voltaic cell, at the cathode, the mass of the electrode
At the cathode: metal ions in solution gain electrons → deposit as solid metal → electrode mass increases.
Identify the oxidizing agent in: Fe + CuSO₄ → FeSO₄ + Cu
Cu²⁺ is REDUCED (gains electrons, goes to Cu). The oxidizing agent is the species that accepts electrons → Cu²⁺.
In electrolysis of water, which gas forms at the cathode?
Cathode = reduction. 2H⁺ + 2e⁻ → H₂. Hydrogen gas forms at cathode; oxygen at anode.
The oxidation number of H in NaH (sodium hydride) is:
In metal hydrides (NaH, CaH₂), hydrogen is −1 (the metal is more electropositive than H).
In a voltaic cell, the anode terminal is:
In a voltaic (galvanic) cell: anode = negative (−); cathode = positive (+). Signs flip in electrolytic cells.
What is the oxidation state of chlorine in KClO₃?
K = +1, O = −2 (×3 = −6). Sum must = 0: +1 + Cl − 6 = 0 → Cl = +5.
In the voltaic cell: Ni²⁺(aq) + Zn(s) → Ni(s) + Zn²⁺(aq), which electrode is the anode?
Zn is oxidized (Zn → Zn²⁺ + 2e⁻) → oxidation occurs at the anode → Zn electrode is the anode.
In the voltaic cell above, what form of energy is converted to electrical energy?
Voltaic cells convert chemical energy (from spontaneous redox reactions) into electrical energy.
Write the half-reaction at the nickel electrode when the cell operates: Ni²⁺(aq) + Zn(s) → Ni(s) + Zn²⁺(aq)
Ni electrode is the cathode (Ni²⁺ is reduced). Half-reaction: Ni²⁺(aq) + 2e⁻ → Ni(s).
In the reaction 4HCl + MnO₂ → MnCl₂ + 2H₂O + Cl₂, what happens to manganese?
In MnO₂: Mn = +4. In MnCl₂: Mn = +2. Oxidation number decreased (+4 → +2) → gained electrons → reduction.
In the reaction 3CuCl₂ + 2Al → 3Cu + 2AlCl₃, what change occurs to the oxidation number of copper?
Cu in CuCl₂ = +2. Cu in product = 0 (free element). Cu²⁺ gains 2 electrons → reduced. Oxidation number: +2 → 0.
In the reaction Mg(s) + 2H⁺(aq) + 2Cl⁻(aq) → Mg²⁺(aq) + 2Cl⁻(aq) + H₂(g), which species undergoes oxidation?
Mg(s) → Mg²⁺: loses 2 electrons → oxidation. Cl⁻ is a spectator; H⁺ gains electrons (reduction).
In 2KClO₃(s) → 2KCl(s) + 3O₂(g), the oxidation state of chlorine changes from
In KClO₃: K=+1, O=−2(×3=−6) → Cl = +5. In KCl: K=+1, Cl=−1. Cl goes from +5 → −1 (gains 6 electrons per Cl → reduction).
In the reaction 2Al + 3Cu²⁺ → 2Al³⁺ + 3Cu, the reduction half-reaction is
Reduction = gain of electrons. Cu²⁺ gains 2e⁻ → Cu. Half-reaction: Cu²⁺ + 2e⁻ → Cu.
In an electrolytic cell, the anode is the
In an electrolytic cell: anode = positive (+) terminal, and oxidation ALWAYS occurs at the anode. (Signs flip from voltaic cell, but anode = oxidation never changes.)
In alpha decay, the mass number changes by:
Alpha particle = ⁴₂He: mass number decreases by 4.
Which type of radiation has no mass and no charge?
Gamma radiation: photon (⁰₀γ) — no mass, no charge, most penetrating.
In beta (β⁻) decay, atomic number:
Beta decay: neutron → proton + electron. One more proton → atomic number +1.
The half-life of a substance is constant. What does it NOT depend on?
Half-life is constant for a given isotope and is unaffected by temperature, pressure, or the amount of sample present — only the isotope's identity determines it.
80 g of a radioisotope decays to 5 g. How many half-lives passed?
80→40→20→10→5: 4 half-lives. Each step = one half-life.
In ²¹⁰₈₃Bi → ⁴₂He + X, what is X?
Mass: 210−4=206. Atomic#: 83−2=81. Element 81 = Thallium → ²⁰⁶₈₁Tl.
Which has the greatest penetrating power?
Gamma has no charge and no mass → penetrates deeply. Stopped only by thick lead or concrete.
Fission produces energy because:
In fission, the products have slightly less mass than reactants → mass deficit converted to energy via E = mc².
Which isotope is used in carbon dating? (t₁/₂ ≈ 5715 yr)
C-14 is radioactive with t₁/₂ = 5715 yr. Living organisms maintain constant C-14; after death it decays.
In nuclear fission of U-235, what sustains the chain reaction?
Each fission releases 2-3 neutrons → these collide with other U-235 nuclei → chain reaction.
A positron (β⁺) has the same mass as an electron but:
Positron: same mass as electron (~0 amu) but opposite charge (+1). It is the antiparticle of the electron.
After 3 half-lives, what fraction of original sample remains?
(½)³ = 1/8 remains after 3 half-lives.
Gamma radiation is stopped by:
Gamma: most penetrating. Requires thick lead or concrete to attenuate significantly.
Which process involves combining light nuclei to form a heavier nucleus?
Fusion: light nuclei (e.g., H isotopes) combine → heavier nucleus + enormous energy. Powers the sun.
In ¹⁴₆C → ⁰₋₁e + X, element X is:
Mass: 14−0=14. Atomic#: 6+1=7 → element 7 = Nitrogen. ¹⁴₇N.
Which medical application uses radiation from I-131?
I-131 (half-life: 8.1 days) is used for diagnosing and treating thyroid conditions — it concentrates in the thyroid.
Nuclear reactions differ from chemical reactions in that nuclear reactions:
Nuclear reactions change proton count → change the element identity (transmutation). Chemical reactions never change the element.
Fusion requires extreme temperatures because:
Nuclei are positively charged → repel each other. Extreme KE (temperature) is needed to overcome this repulsion and bring nuclei close enough to fuse.
Which type of decay does NOT change the mass number?
Beta: mass unchanged, atomic# +1. Positron: mass unchanged, atomic# −1. Gamma: no changes. Alpha: mass −4. So beta, positron, and gamma don't change mass number.
A 100 g sample with t₁/₂ = 20 years. How much remains after 60 years?
60 ÷ 20 = 3 half-lives. (½)³ × 100 = 12.5 g.
A radioactive emission travels straight through an electric field without being deflected. It is:
Gamma radiation has no charge → not deflected by electric or magnetic fields. Alpha (+2) deflects toward negative plate; beta (−1) and positron (+1) deflect in opposite directions.
Based on Table N, what is the decay mode of tritium (H-3)?
Table N: H-3 (tritium) undergoes beta-minus (β⁻) decay. A neutron converts to a proton + high-speed electron.
H-3 has a half-life of 12.31 years. What fraction of an original sample remains after 36.93 years?
36.93 ÷ 12.31 = 3 half-lives. Fraction remaining = (½)³ = 1/8.
In the nuclear equation: ⁶₃Li + ¹₀n → ³₁H + ⁴₂He, this reaction is an example of:
A neutron bombards the nucleus of a light, stable isotope (Li-6) and converts it into different nuclei (H-3 and He-4). Since a light target is transformed by particle bombardment — not decaying spontaneously, and not the splitting of a heavy nucleus like U-235 — this is an artificial transmutation.
Nuclear fusion in the Sun results from the conversion of:
E = mc². In fusion, mass of products is slightly less than mass of reactants → this mass deficit is converted to enormous energy (Einstein's equation).
Which radioisotope is used for diagnosing thyroid disorders?
I-131 concentrates in the thyroid gland and is used for diagnosing and treating thyroid conditions (Table N).
The ratio of the mass of U-238 to the mass of Pb-206 in a rock sample can be used to
U-238 decays through a series of steps to Pb-206. The U-238/Pb-206 ratio reflects how long the process has been occurring → geological dating.
Which pair of nuclides is used to date the remains of a once-living organism?
C-14 (radioactive, t½ = 5715 yr) decays after death. Comparing C-14 to stable C-12 gives the age. U-238 is for geological (inorganic) dating.
In a nuclear fusion reaction, mass is lost because
E = mc². In fusion, the product nuclei have slightly less mass than the original nuclei. This mass deficit is converted to enormous energy.
Which sample of radioisotope emits particles with the greatest mass?
Fr-220 is a heavy isotope — it decays by alpha emission (mass 4). Fr-220 emits the most massive particles. Tritium emits beta particles (mass ≈ 0).
Which general formula represents the alkene homologous series?
Alkenes have one double bond: CₙH₂ₙ. Alkanes = CₙH₂ₙ₊₂; Alkynes = CₙH₂ₙ₋₂.
Which compound belongs to the homologous series with general formula CₙH₂ₙ?
CₙH₂ₙ: n=3 → C₃H₆ ✓. C₂H₂ = alkyne (CₙH₂ₙ₋₂). C₄H₁₀ = alkane (CₙH₂ₙ₊₂). C₅H₈ doesn't fit.
Which reaction produces an alcohol from glucose?
Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. Glucose → ethanol (an alcohol) using yeast, anaerobic conditions.
The element that makes a compound organic is:
Organic compounds are defined by the presence of carbon. All organic compounds contain C (usually with H).
A carboxylic acid reacts with an alcohol. What type of reaction is this?
Acid + alcohol → ester + water. This is esterification.
What are the products of esterification?
Esterification: carboxylic acid + alcohol → ester + H₂O.
Propanoic acid (CH₃CH₂COOH) and ethyl methanoate (HCOOCH₂CH₃) are isomers because they:
Isomers: same molecular formula (C₃H₆O₂) but different structural formulas (atoms connected differently) → different compounds.
Which functional group is present in ethanol (CH₃CH₂OH)?
The −OH group is the alcohol functional group. Ethanol = CH₃CH₂OH.
A reaction in which atoms are added across a double bond is called:
Addition reaction: atoms (like H₂, Cl₂) add across a C=C double bond. Alkene + H₂ → alkane (hydrogenation).
What is the IUPAC name for the compound with a 6-carbon chain and a CH₃ branch on carbon 3?
6-carbon chain = hex; CH₃ branch on C3 = 3-methyl. Name: 3-methylhexane.
A compound has the formula CₙH₂ₙ₊₂. What class of organic compounds does it belong to?
CₙH₂ₙ₊₂ = alkanes (saturated hydrocarbons, single bonds only).
In organic naming, the prefix 'but-' indicates how many carbon atoms?
Table Q prefixes: meth=1, eth=2, prop=3, but=4, pent=5, hex=6.
Which is a correct statement about homologous series?
Homologous series: each member differs from the next by one CH₂ unit (14 g/mol). Same functional group, gradually changing properties.
Which substance is a product of the complete combustion of a hydrocarbon?
Complete combustion of any hydrocarbon: CₓHᵧ + O₂ → CO₂ + H₂O. Always CO₂ and H₂O.
A student is given a structural formula showing H−C−OH with additional H atoms. What functional group is present?
−OH attached to a carbon chain = alcohol functional group.
Based on Table R, methanoic acid (HCOOH) belongs to which class of compound is it?
HCOOH = methanoic acid = simplest carboxylic acid. Functional group: −COOH.
Which organic compound is formed when a carboxylic acid reacts with an alcohol and water is removed?
Esterification: R−COOH + HO−R' → R−COO−R' (ester) + H₂O.
How many electrons are shared in a C−C single bond?
A single bond = 1 shared pair = 2 electrons.
Two compounds with the same molecular formula but different structural formulas are:
Isomers: same molecular formula (e.g., C₄H₁₀), different structural formulas → different compounds with different properties.
Which is NOT an organic compound?
CO₂ is considered inorganic (along with CO, carbonates, cyanides) even though it contains carbon. The others are organic.
In esterification, what small molecule is released as a product?
Acid + alcohol → ester + WATER. The H from the acid's −OH and the −OH from the alcohol combine to form H₂O.
What type of organic reaction joins many small monomer molecules into a large polymer?
Polymerization: monomers (small repeating units) bond together to form a polymer (e.g., ethene → polyethylene, amino acids → proteins).
Ethane (C₂H₆) belongs to the alkane series. Its molecular formula fits CₙH₂ₙ₊₂ with n=2. What is the next member of the series?
Next alkane after ethane (C₂H₆): add CH₂ → C₃H₈ = propane. Fits CₙH₂ₙ₊₂ with n=3: 2(3)+2 = 8 ✓.
Which compound is an alcohol?
CH₃OH = methanol. Contains −OH group → alcohol. CH₃COOH = acid; CH₃CHO = aldehyde; CH₃COCH₃ = ketone.
A substance reacts with NaOH (saponification). What type of organic compound is it?
Saponification: ester + base (NaOH) → soap (fatty acid salt) + alcohol. The reactant that undergoes saponification is an ester.
What is the name for a reaction where one atom in an organic molecule is replaced by another atom?
Substitution: one atom (e.g., H) is replaced by another (e.g., Cl) in an organic molecule. Common with alkanes + halogens.
Ethanol (C₂H₅OH) and dimethyl ether (CH₃OCH₃) both have molecular formula C₂H₆O. They are:
Same molecular formula (C₂H₆O) but different structural formulas → isomers.
What is the name for the series of organic compounds where each member has one more CH₂ than the previous member?
A homologous series is a family of organic compounds each differing by CH₂, sharing the same functional group and general formula.
The functional group −COOH is found in:
−COOH (carboxyl group) is the defining functional group of carboxylic acids (e.g., acetic acid, methanoic acid).
Ethene (C₂H₄) undergoes addition with H₂. The product is:
Addition: C₂H₄ + H₂ → C₂H₆ (ethane). The double bond is broken and H atoms add across it, converting the alkene to an alkane.
Which formula represents an unsaturated hydrocarbon?
Unsaturated = has at least one double or triple bond. C₃H₄ fits CₙH₂ₙ₋₂ (alkyne: n=3 → 2(3)−2=4). The others all fit CₙH₂ₙ₊₂ (alkanes = saturated).
Which pair of compounds are isomers of each other?
C₂H₅OH (ethanol) and CH₃OCH₃ (dimethyl ether) both have formula C₂H₆O — same molecular formula, different structures → isomers.
According to Table R, which type of reaction produces an ester?
Esterification: carboxylic acid + alcohol → ester + water. The product is an ester (R-COO-R').
Which organic compound is classified as an alcohol?
C₂H₅OH = ethanol. It contains the −OH functional group → classified as an alcohol. HCOOH = acid; CH₃CHO = aldehyde; CH₃COCH₃ = ketone.
| Decay Type | Symbol | Mass # Change | Atomic # Change | Penetration |
|---|---|---|---|---|
| Alpha (α) | ⁴₂He | −4 | −2 | Stopped by paper |
| Beta⁻ (β⁻) | ⁰₋₁e | 0 | +1 | Stopped by aluminum |
| Positron (β⁺) | ⁰₊₁e | 0 | −1 | Stopped by aluminum |
| Gamma (γ) | ⁰₀γ | 0 | 0 | Needs lead/concrete |
| Indicator | Transition pH | Acid Color | Base Color |
|---|---|---|---|
| Methyl orange | 3.1–4.4 | Red | Yellow |
| Bromcresol green | 3.8–5.4 | Yellow | Blue |
| Litmus | 4.5–8.3 | Red | Blue |
| Bromthymol blue | 6.0–7.6 | Yellow | Blue |
| Thymol blue | 8.0–9.6 | Yellow | Blue |
| Phenolphthalein | 8.2–10.0 | Colorless | Pink/Fuchsia |
| # Half-Lives | Fraction Left | % Remaining | % Decayed |
|---|---|---|---|
| 0 | 1 | 100% | 0% |
| 1 | 1/2 | 50% | 50% |
| 2 | 1/4 | 25% | 75% |
| 3 | 1/8 | 12.5% | 87.5% |
| 4 | 1/16 | 6.25% | 93.75% |
| 5 | 1/32 | 3.125% | 96.875% |
| Bonding Pairs | Lone Pairs | Geometry | Bond Angle | Example |
|---|---|---|---|---|
| 2 | 0 | Linear | 180° | CO₂, BeCl₂ |
| 3 | 0 | Trigonal planar | 120° | BF₃, SO₃ |
| 4 | 0 | Tetrahedral | 109.5° | CH₄, CCl₄ |
| 3 | 1 | Trigonal pyramidal | 107° | NH₃ |
| 2 | 2 | Bent/V-shaped | 104.5° | H₂O |
| Property | Voltaic (Galvanic) Cell | Electrolytic Cell |
|---|---|---|
| Energy conversion | Chemical → Electrical | Electrical → Chemical |
| Spontaneous? | Yes | No (needs external power) |
| Anode sign | Negative (−) | Positive (+) |
| Cathode sign | Positive (+) | Negative (−) |
| At anode | Oxidation (always) | Oxidation (always) |
| At cathode | Reduction (always) | Reduction (always) |
| Electron flow | Anode → Cathode (wire) | Cathode ← Anode (wire) |
| ΔEN Range | Bond Type | Example |
|---|---|---|
| 0 – 0.4 | Nonpolar covalent | Cl-Cl, C-H, H-H |
| 0.4 – 1.7 | Polar covalent | H-O, H-N, H-Cl |
| ≥ 1.7 | Ionic | Na-Cl, Mg-O, Ca-F |
| Law | Formula | Constant | Relationship |
|---|---|---|---|
| Boyle's | P₁V₁ = P₂V₂ | T, n | P and V inverse |
| Charles's | V₁/T₁ = V₂/T₂ | P, n | V and T direct |
| Gay-Lussac's | P₁/T₁ = P₂/T₂ | V, n | P and T direct |
| Combined | P₁V₁/T₁ = P₂V₂/T₂ | n | All three |
| Avogadro's | Equal V at same T,P = equal n | T, P | V and n direct |
| Series | General Formula | Bond Type | Example |
|---|---|---|---|
| Alkanes | CₙH₂ₙ₊₂ | Single only (saturated) | CH₄, C₂H₆, C₃H₈ |
| Alkenes | CₙH₂ₙ | One double bond | C₂H₄, C₃H₆ |
| Alkynes | CₙH₂ₙ₋₂ | One triple bond | C₂H₂ (acetylene) |
| Cycloalkanes | CₙH₂ₙ | Ring, single bonds | C₃H₆ (cyclopropane) |
| Functional Group | Name Class | Suffix | Example |
|---|---|---|---|
| −OH | Alcohol | -ol | ethanol (C₂H₅OH) |
| −COOH | Carboxylic acid | -oic acid | ethanoic acid (CH₃COOH) |
| −COO− | Ester | -anoate | ethyl ethanoate |
| −CHO | Aldehyde | -al | methanal (formaldehyde) |
| C=O (chain) | Ketone | -one | propanone (acetone) |
| −NH₂ | Amine | -amine | methylamine |
| Reaction (Table R) | Reactants | Products | Key fact |
|---|---|---|---|
| Fermentation | C₆H₁₂O₆ | 2C₂H₅OH + 2CO₂ | Yeast, anaerobic, makes alcohol |
| Esterification | Acid + Alcohol | Ester + H₂O | Reversible |
| Saponification | Ester + NaOH | Soap + Alcohol | Reverse of esterification |
| Addition | Alkene + H₂/Cl₂ | Saturated product | Breaks double bond |
| Substitution | Alkane + halogen | Haloalkane + HX | Replaces H with halogen |
| Combustion | CₓHᵧ + O₂ | CO₂ + H₂O | Complete combustion always |
| Polymerization | n(monomer) | Polymer | Ethene → polyethylene |
| Property | Across Period (L→R) | Down Group (↓) | Largest Value |
|---|---|---|---|
| Atomic radius | Decreases | Increases | Fr (bottom-left) |
| Ionization energy | Increases | Decreases | He (top-right) |
| Electronegativity | Increases | Decreases | F (4.0) |
| Metallic character | Decreases | Increases | Fr (bottom-left) |
| Ionic radius (cations) | Decreases | Increases | Cs⁺ |
| Compound | ΔH (dissolving) | Type | Effect on solution |
|---|---|---|---|
| NaOH(s) | Negative (−) | Exothermic | Solution gets WARM |
| NH₄NO₃(s) | Positive (+) | Endothermic | Solution gets COLD (cold packs) |
| KNO₃(s) | Positive (+) | Endothermic | Solution gets COLD |
| NH₄Cl(s) | Positive (+) | Endothermic | Solution gets COLD |
| Type | Example | What's equal | Closed system? |
|---|---|---|---|
| Physical equilibrium | Sealed flask with liquid H₂O | Evaporation rate = condensation rate | Yes |
| Chemical equilibrium | N₂ + 3H₂ ⇌ 2NH₃ | Forward rate = reverse rate | Yes |