ACS General Chemistry Practice Test 12
60 original exam-style multiple-choice questions with answers & explanations — covering every major topic tested on the ACS General Chemistry exam.
Note: These are original practice questions written in the ACS exam style — not reproduced exam questions. Use them to test your readiness for the real ACS General Chemistry exam.
📱 How to use: Try each question first, then click “Show Answer” to check. Covers: atomic structure, bonding, stoichiometry, gases, thermochemistry, kinetics, equilibrium, acids & bases, electrochemistry and more.
⚛ Atomic Structure & Periodic Trends
Q1Which atom has the smallest atomic radius?
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Correct: (B)
Atomic radius decreases up a group and F is the smallest halogen listed.
Q2Which element has the highest first ionization energy?
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Correct: (A)
Ionization energy increases across Period 2 (with the Be/B exception); C has the highest value here.
Q3What is the ground-state electron configuration of Cr3+?
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Correct: (C)
Neutral Cr is [Ar]4s1 3d5; removing three electrons (4s first, then 3d) gives [Ar]3d3.
Q4Which is the most electronegative element?
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Correct: (B)
F is the most electronegative element in the periodic table.
Q5Which isoelectronic ion (18 electrons) has the smallest radius?
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Correct: (A)
All have 18 electrons; K+ (Z = 19) has the highest nuclear charge and pulls electrons in most tightly.
Q6Which element has the highest second ionization energy?
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Correct: (C)
K+ has a stable noble-gas (argon) configuration, so removing a second electron requires very high energy.
🔬 Chemical Bonding & Molecular Geometry
Q7What is the molecular geometry of NH3?
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Correct: (B)
NH3 has 4 electron domains (3 bonds + 1 lone pair); the lone pair compresses the shape to trigonal pyramidal.
Q8What is the hybridization of sulfur in SF6?
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Correct: (A)
SF6 has 6 bonding domains in an octahedral arrangement, requiring sp3d2 hybridization.
Q9Which molecule has the longest bond length?
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Correct: (C)
I2 has the largest atoms, so its bond is the longest of these single bonds.
Q10Which molecule is polar?
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Correct: (B)
H2O is bent, so its bond dipoles do not cancel; the others are symmetric and nonpolar.
Q11What is the bond order of N2?
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Correct: (A)
N2 has a triple bond: (10 bonding – 4 antibonding)/2 = 3.0.
Q12Which has the smallest dipole moment?
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Correct: (C)
HI has the smallest electronegativity difference, giving the least polar bond.
Q13What is the molecular geometry of XeF2?
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Correct: (B)
XeF2 has 5 electron domains (2 bonds + 3 lone pairs); the lone pairs occupy equatorial positions, leaving a linear molecule.
🧪 Stoichiometry & Aqueous Reactions
Q144.0 g of H2 reacts with excess O2 (2H2 + O2 → 2H2O). What mass of H2O is produced? (H2 = 2.02 g/mol, H2O = 18.02 g/mol)
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Correct: (A)
Moles H2 = 4.0/2.02 = 1.98 mol; 1:1 mole ratio gives 1.98 mol H2O × 18.02 g/mol ≈ 36 g.
Q15The actual yield of a reaction is 8.0 g and the theoretical yield is 10.0 g. What is the percent yield?
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Correct: (D)
(8.0/10.0) × 100% = 80%.
Q16A compound contains 27.3% C and 72.7% O by mass. What is its empirical formula?
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Correct: (C)
Moles: C = 27.3/12.01 = 2.27, O = 72.7/16.00 = 4.54; ratio 1:2 gives CO2.
Q17How many moles of solute are in 250 mL of 2.0 M NaCl solution?
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Correct: (B)
Moles = M × V = (2.0 mol/L)(0.250 L) = 0.50 mol.
Q18What is the net ionic equation for Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)?
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Correct: (A)
PbI2 is the precipitate; K+ and NO3- are spectators.
Q19What is the oxidation number of sulfur in H2SO4?
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Correct: (D)
2(+1) + S + 4(-2) = 0 gives S = +6.
Q20How many moles of O2 are needed to burn 1.0 mol of CH4? (CH4 + 2O2 → CO2 + 2H2O)
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Correct: (C)
The balanced equation requires 2 mol O2 per 1 mol CH4.
🌀 Gases & Intermolecular Forces
Q21A gas occupies 3.0 L at 300 K. What volume will it occupy at 600 K if pressure is held constant?
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Correct: (B)
By Charles's law (V1/T1 = V2/T2), V2 = (3.0 L)(600 K)/(300 K) = 6.0 L.
Q22How much faster does He effuse than O2 at the same temperature?
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Correct: (A)
By Graham's law, rate ratio = √(M_O2/M_He) = √(32.00/4.00) = √8 = 2.83.
Q23Which noble gas is most easily liquefied?
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Correct: (D)
Xe has the largest, most polarizable atoms, giving the strongest London dispersion forces.
Q24Which substance has the strongest intermolecular forces?
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Correct: (C)
HF exhibits hydrogen bonding, stronger than the dipole-dipole and dispersion forces in the others.
Q25Which substance has the highest vapor pressure at 25°C?
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Correct: (B)
CH4 has only weak London dispersion forces, so it evaporates most readily.
🔥 Thermochemistry
Q26Given: X → Y, ΔH = -100 kJ; Y → Z, ΔH = +50 kJ. What is ΔH for X → Z?
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Correct: (D)
By Hess's law, add the steps: -100 + 50 = -50 kJ.
Q27What is ΔH for 2H2(g) + O2(g) → 2H2O(l)? (ΔHf° of H2O(l) = -285.8 kJ/mol)
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Correct: (A)
ΔH = 2(-285.8) – 0 = -571.6 kJ ≈ -572 kJ.
Q28How much heat is released when 100 g of water cools from 30°C to 20°C? (c = 4.184 J/g·°C)
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Correct: (C)
q = (100 g)(4.184 J/g·°C)(10°C) = 4184 J = 4.18 kJ released.
Q29Estimate ΔH for N2(g) + 3H2(g) → 2NH3(g) using bond enthalpies (N≡N = 945, H-H = 436, N-H = 391 kJ/mol).
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Correct: (B)
ΔH = [945 + 3(436)] – [6(391)] = 2253 – 2346 = -93 kJ.
Q30Which process is exothermic?
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Correct: (A)
Combustion releases heat; the others all absorb heat.
Q31A 25.0 g sample of a metal absorbs 500 J of heat and its temperature rises by 10.0°C. What is the specific heat of the metal?
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Correct: (D)
c = q/(mΔT) = 500 J / [(25.0 g)(10.0°C)] = 2.0 J/g·°C.
⚡ Quantum Theory & Electronic Structure
Q32Which set of quantum numbers is allowed?
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Correct: (C)
Valid sets require l < n and |ml| ≤ l; only (C) satisfies both.
Q33What is the energy of a photon with wavelength 600 nm?
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Correct: (B)
E = hc/λ = (6.626 × 10-34)(3.00 × 108)/(600 × 10-9) = 3.31 × 10-19 J.
Q34What is the de Broglie wavelength of an electron moving at 2.0 × 106 m/s? (me = 9.11 × 10-31 kg)
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Correct: (A)
λ = h/mv = 6.626 × 10-34 / [(9.11 × 10-31)(2.0 × 106)] = 3.6 × 10-10 m.
Q35Which orbital has 1 radial node and 2 angular nodes?
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Correct: (D)
Angular nodes = l = 2 (d orbital); radial nodes = n – l – 1 = 1 gives n = 4, so 4d.
⏱ Chemical Kinetics
Q36For the rate law rate = k[A][B], what happens to the rate if both [A] and [B] are doubled?
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Correct: (C)
Rate ∝ [A][B], so (2)(2) = 4 times the original rate.
Q37The minimum energy that reactant molecules must possess for a reaction to occur is called the:
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Correct: (B)
The activation energy (Ea) is the energy barrier between reactants and the transition state.
Q38What fraction of reactant remains after 2 half-lives for a first-order reaction?
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Correct: (A)
After each half-life half remains: (1/2)2 = 1/4.
Q39Which of the following is NOT changed by the presence of a catalyst?
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Correct: (D)
A catalyst speeds up both forward and reverse reactions equally, so ΔG (a state function) is unchanged.
Q40Tripling the concentration of A increases the reaction rate by a factor of 9. What is the order of the reaction with respect to A?
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Correct: (C)
32 = 9, so the reaction is second order in A.
Q41A proposed mechanism has the slow step: 2A → B. What is the rate law?
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Correct: (B)
The rate law follows the stoichiometry of the slow (rate-determining) elementary step.
⇆ Chemical Equilibrium
Q42What is the Kc expression for 2NO2(g) ⇌ N2O4(g)?
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Correct: (A)
Kc = [products]/[reactants] with stoichiometric coefficients as exponents.
Q43For N2(g) + 3H2(g) ⇌ 2NH3(g), increasing the total pressure shifts the equilibrium:
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Correct: (D)
Higher pressure favors the side with fewer gas moles (2 vs 4).
Q44For CaCO3(s) ⇌ CaO(s) + CO2(g), what is the relationship between Kp and Kc?
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Correct: (C)
Δn = 1 – 0 = 1 (solids omitted), so Kp = Kc(RT)1.
Q45If Q > K for a reaction, what will happen?
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Correct: (D)
When Q > K, the system has excess products and shifts left to reach equilibrium.
Q46If Kc = 1.0 × 10-8 for a reaction, the equilibrium mixture consists mainly of:
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Correct: (A)
A very small K means the equilibrium lies far to the left.
Q47The Ksp of PbI2 is 3.2 × 10-11. What is its molar solubility in water?
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Correct: (D)
For PbI2 ⇌ Pb2+ + 2I-, Ksp = (s)(2s)2 = 4s3, so s = ∛(3.2 × 10-11/4) = 2.0 × 10-4 M.
🧫 Acids, Bases & Buffers
Q48What is the pH of 0.0010 M NaOH?
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Correct: (B)
[OH-] = 0.0010 M gives pOH = 3.00, so pH = 14.00 – 3.00 = 11.00.
Q49A 0.10 M solution of a weak acid has pH 4.00. What is its Ka?
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Correct: (C)
[H+] = 10-4 M; Ka ≈ [H+]2/[HA] = (10-4)2/0.10 = 1.0 × 10-7.
Q50A buffer has [A-]/[HA] = 2.0 and the acid has pKa = 4.00. What is the pH?
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Correct: (D)
pH = pKa + log([A-]/[HA]) = 4.00 + log(2.0) = 4.00 + 0.30 = 4.30.
Q51In a strong acid-strong base titration, what is the pH at the equivalence point?
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Correct: (A)
Only neutral water and spectator ions remain, so pH = 7.00.
Q52What is the conjugate acid of NH3?
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Correct: (D)
Adding one H+ to NH3 gives NH4+.
Q53Which salt gives an acidic solution when dissolved in water?
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Correct: (B)
NH4+ is the conjugate acid of a weak base and hydrolyzes to produce H3O+.
🔋 Thermodynamics & Electrochemistry
Q54Which process decreases the entropy of the system?
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Correct: (C)
Three moles of gas become two moles of liquid, greatly reducing disorder.
Q55A reaction has ΔH > 0 and ΔS > 0. Under what condition is it spontaneous?
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Correct: (A)
ΔG = ΔH – TΔS becomes negative when T is large enough that TΔS > ΔH.
Q56If E°cell for a redox reaction is negative, the reaction is:
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Correct: (D)
A negative E°cell gives positive ΔG°, meaning the reaction is nonspontaneous as written.
Q57How many moles of electrons flow through a circuit with a current of 1.50 A for 20.0 minutes?
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Correct: (B)
Charge = (1.50 A)(1200 s) = 1800 C; mol e- = 1800/96485 = 0.0187 mol.
Q58What is ΔG° for a cell with E° = 0.50 V and n = 1?
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Correct: (C)
ΔG° = -nFE° = -(1)(96485)(0.50) = -48,242 J ≈ -48.2 kJ.
☢ Nuclear & Descriptive Chemistry
Q59In the decay 14C6 → 14N7 + X, what is particle X?
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Correct: (D)
Atomic number increases by 1 with no mass change, characteristic of beta (electron) emission.
Q60Which gas turns limewater milky?
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Correct: (D)
CO2 reacts with Ca(OH)2 to form white CaCO3 precipitate, turning limewater milky.
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