ACS General Chemistry Practice Test 11
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 of the following atoms has the largest atomic radius?
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Correct: (A)
Atomic radius decreases from left to right across a period as effective nuclear charge increases; Na is furthest left in Period 3.
Q2Which element has the highest first ionization energy?
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Correct: (C)
First ionization energy generally increases across a period; Ne, as a noble gas with a full octet, holds its electrons most tightly.
Q3What is the ground-state electron configuration of Fe2+?
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Correct: (B)
Neutral Fe is [Ar]4s2 3d6; when forming Fe2+, the 4s electrons are removed first, leaving [Ar]3d6.
Q4Which element is the most electronegative?
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Correct: (D)
Electronegativity decreases down a group as atomic size increases; Cl is the smallest and most electronegative of these halogens.
Q5Which of the following ions has the smallest ionic radius? (All are isoelectronic with 10 electrons.)
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Correct: (D)
For isoelectronic species, radius decreases as nuclear charge increases; Mg2+ (Z = 12) has the greatest proton attraction.
Q6Which element has the highest second ionization energy?
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Correct: (A)
Removing a second electron from Na+ disrupts a stable noble-gas (neon) core, requiring far more energy than for the others.
🔬 Chemical Bonding & Molecular Geometry
Q7What is the molecular geometry of SF4?
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Correct: (B)
SF4 has 5 electron domains (4 bonding pairs + 1 lone pair); the lone pair occupies an equatorial position, giving a seesaw shape.
Q8What is the hybridization of the central atom in XeF4?
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Correct: (C)
XeF4 has 6 electron domains (4 bonds + 2 lone pairs) in an octahedral arrangement, requiring sp3d2 hybridization.
Q9Which molecule has the shortest bond length?
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Correct: (A)
N2 has a triple bond (bond order 3); higher bond order means shorter, stronger bonds.
Q10Which molecule is nonpolar?
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Correct: (C)
CO2 is linear (O=C=O), so the two equal bond dipoles cancel exactly.
Q11What is the bond order of O2+?
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Correct: (C)
O2 has bond order 2.0; removing one electron from an antibonding (π*) orbital increases the bond order by 0.5, giving 2.5.
Q12Which molecule has the largest dipole moment?
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Correct: (D)
HF has the largest electronegativity difference between its atoms, producing the most polar bond.
Q13What is the molecular geometry of ClF3?
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Correct: (B)
ClF3 has 5 electron domains (3 bonds + 2 lone pairs); both lone pairs occupy equatorial positions, giving a T-shape.
🧪 Stoichiometry & Aqueous Reactions
Q1410.0 g of CaCO3 decomposes according to CaCO3 → CaO + CO2. What mass of CO2 is produced? (Molar masses: CaCO3 = 100.1 g/mol, CO2 = 44.01 g/mol)
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Correct: (A)
Moles CaCO3 = 10.0/100.1 = 0.0999 mol; 1:1 stoichiometry gives 0.0999 mol CO2 × 44.01 g/mol = 4.40 g.
Q15A reaction gives 5.00 g of product, but the theoretical yield is 6.25 g. What is the percent yield?
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Correct: (B)
Percent yield = (actual/theoretical) × 100% = (5.00/6.25) × 100% = 80.0%.
Q16A compound contains 40.0% C, 6.7% H, and 53.3% O by mass. What is its empirical formula?
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Correct: (A)
Moles: C = 40.0/12.01 = 3.33, H = 6.7/1.008 = 6.65, O = 53.3/16.00 = 3.33; dividing by 3.33 gives 1:2:1, so CH2O.
Q17What volume of 6.00 M HCl is needed to prepare 500 mL of 1.50 M HCl?
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Correct: (D)
M1V1 = M2V2 gives V1 = (1.50 M)(0.500 L)/(6.00 M) = 0.125 L = 125 mL.
Q18What is the net ionic equation for the reaction of aqueous AgNO3 with aqueous NaCl?
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Correct: (C)
AgCl precipitates; Na+ and NO3- are spectator ions and cancel out.
Q19What is the oxidation number of Cr in K2Cr2O7?
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Correct: (C)
2(+1) + 2(Cr) + 7(-2) = 0 gives 2(Cr) = +12, so Cr = +6.
Q20How many moles of O2 are required to burn 2.0 mol of C3H8? (C3H8 + 5O2 → 3CO2 + 4H2O)
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Correct: (B)
The balanced equation shows 5 mol O2 per 1 mol C3H8, so 2.0 × 5 = 10 mol O2.
🌀 Gases & Intermolecular Forces
Q21A gas occupies 2.50 L at 1.00 atm and 298 K. If the volume is reduced to 1.25 L at constant temperature, what is the new pressure?
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Correct: (A)
By Boyle's law (P1V1 = P2V2), P2 = (1.00 atm)(2.50 L)/(1.25 L) = 2.00 atm.
Q22Which gas effuses fastest at the same temperature?
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Correct: (D)
By Graham's law, the lightest gas effuses fastest; H2 (M = 2.02 g/mol) is the lightest.
Q23Which gas deviates most from ideal behavior at high pressure?
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Correct: (D)
Xe atoms are the largest and most polarizable, so intermolecular attractions and molecular volume effects are greatest.
Q24Which substance has the strongest intermolecular forces?
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Correct: (B)
H2O exhibits hydrogen bonding, which is stronger than the London dispersion forces in the others.
Q25Which compound has the highest boiling point?
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Correct: (B)
Ethanol can hydrogen-bond, giving it much stronger intermolecular attractions than the others.
🔥 Thermochemistry
Q26Given: C(s) + O2(g) → CO2(g), ΔH = -394 kJ; CO(g) + ½O2(g) → CO2(g), ΔH = -283 kJ. What is ΔH for C(s) + ½O2(g) → CO(g)?
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Correct: (A)
Reverse the second equation (+283 kJ) and add to the first: -394 + 283 = -111 kJ.
Q27Using ΔHf° values (CH4(g) = -74.8, CO2(g) = -393.5, H2O(l) = -285.8 kJ/mol), what is ΔH for CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)?
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Correct: (D)
ΔH = [-393.5 + 2(-285.8)] – [-74.8] = -965.1 + 74.8 = -890 kJ.
Q28How much heat is absorbed when 50.0 g of water is heated from 20.0°C to 40.0°C? (specific heat = 4.184 J/g·°C)
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Correct: (D)
q = mcΔT = (50.0 g)(4.184 J/g·°C)(20.0°C) = 4184 J = 4.18 kJ.
Q29Estimate ΔH for H2(g) + Cl2(g) → 2HCl(g) using bond enthalpies (H-H = 436, Cl-Cl = 242, H-Cl = 431 kJ/mol).
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Correct: (C)
ΔH = (bonds broken) – (bonds formed) = (436 + 242) – 2(431) = 678 – 862 = -184 kJ.
Q30A reaction absorbs heat from its surroundings. What is the sign of ΔH?
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Correct: (D)
Heat absorption means the system gains enthalpy, so ΔH > 0 (endothermic).
Q31How much heat is required to melt 18.0 g of ice at 0°C? (ΔHfus = 6.01 kJ/mol)
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Correct: (D)
18.0 g H2O ÷ 18.02 g/mol ≈ 1.00 mol; (1.00 mol)(6.01 kJ/mol) = 6.01 kJ.
⚡ Quantum Theory & Electronic Structure
Q32Which set of quantum numbers is NOT allowed?
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Correct: (C)
The angular momentum quantum number l must be less than n; l = 1 is not allowed when n = 1.
Q33What is the energy of a photon with wavelength 500 nm? (h = 6.626 × 10-34 J·s, c = 3.00 × 108 m/s)
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Correct: (A)
E = hc/λ = (6.626 × 10-34)(3.00 × 108)/(500 × 10-9) = 3.98 × 10-19 J.
Q34What is the de Broglie wavelength of an electron moving at 1.0 × 106 m/s? (me = 9.11 × 10-31 kg)
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Correct: (D)
λ = h/mv = 6.626 × 10-34 / [(9.11 × 10-31)(1.0 × 106)] = 7.3 × 10-10 m.
Q35Which orbital has 2 radial nodes and 1 angular node?
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Correct: (B)
Angular nodes = l = 1 (p orbital); radial nodes = n – l – 1 = 2 gives n = 4, so 4p.
⏱ Chemical Kinetics
Q36For a reaction, doubling [A] doubles the rate and doubling [B] quadruples the rate. What is the rate law?
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Correct: (B)
The reaction is first order in A (rate ∝ [A]) and second order in B (rate ∝ [B]2).
Q37For the rate law rate = k[A]2, with rate in M/s, what are the units of k?
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Correct: (B)
M/s = k·M2, so k has units of 1/(M·s) = M-1·s-1.
Q38A first-order reaction has a half-life of 20 min. What fraction of reactant remains after 60 min?
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Correct: (C)
60 min is 3 half-lives, so (1/2)3 = 1/8 remains.
Q39How does a catalyst increase the rate of a reaction?
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Correct: (B)
A catalyst provides an alternative pathway with lower activation energy; it is not consumed.
Q40Which factor does NOT affect the value of the rate constant k?
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Correct: (C)
The rate constant depends on temperature and activation energy (Arrhenius equation), not on concentrations.
Q41A mechanism has Step 1 (slow): A → B; Step 2 (fast): B + C → D. What is the rate law?
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Correct: (A)
The rate law is determined by the slow (rate-determining) step, which involves only A.
⇆ Chemical Equilibrium
Q42What is the Kc expression for N2(g) + 3H2(g) ⇌ 2NH3(g)?
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Correct: (D)
Kc = [products]coefficients/[reactants]coefficients = [NH3]2/([N2][H2]3).
Q43For an exothermic reaction at equilibrium, increasing the temperature shifts the equilibrium in which direction?
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Correct: (B)
Heat is a product in an exothermic reaction; adding heat shifts equilibrium toward reactants (Le Châtelier's principle).
Q44For H2(g) + I2(g) ⇌ 2HI(g), what is the relationship between Kp and Kc?
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Correct: (C)
Δn = 2 – 2 = 0, so Kp = Kc(RT)0 = Kc.
Q45A reaction has Kc = 1.0 × 105 at 298 K. What does this indicate about the equilibrium position?
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Correct: (A)
A very large K means the equilibrium lies far to the right (products favored).
Q46If Q < K for a reaction, in which direction will it proceed to reach equilibrium?
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Correct: (C)
When Q < K, the reaction shifts right (toward products) to increase Q until Q = K.
Q47The Ksp of AgCl is 1.8 × 10-10. What is its molar solubility in pure water?
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Correct: (D)
For AgCl ⇌ Ag+ + Cl-, Ksp = s2, so s = √(1.8 × 10-10) = 1.3 × 10-5 M.
🧫 Acids, Bases & Buffers
Q48What is the pH of 0.010 M HCl?
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Correct: (A)
HCl is a strong acid: [H+] = 0.010 M, so pH = -log(0.010) = 2.00.
Q49A 0.10 M solution of weak acid HA has pH 3.00. What is Ka?
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Correct: (C)
[H+] = 10-3 M; Ka = [H+]2/[HA] = (10-3)2/0.10 = 1.0 × 10-5.
Q50What is the pH of a buffer with [HA] = 0.20 M, [A-] = 0.10 M, and Ka = 1.0 × 10-5?
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Correct: (B)
pH = pKa + log([A-]/[HA]) = 5.00 + log(0.10/0.20) = 5.00 – 0.30 = 4.70.
Q51In the titration of a weak acid with a strong base, what is the pH at the equivalence point?
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Correct: (C)
The conjugate base of the weak acid hydrolyzes (A- + H2O ⇌ HA + OH-), making the solution basic.
Q52What is the conjugate base of H2PO4-?
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Correct: (A)
Removing one H+ from H2PO4- gives HPO4 2-.
Q53Which salt produces a basic solution when dissolved in water?
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Correct: (D)
CH3COO- is the conjugate base of a weak acid and hydrolyzes to produce OH-; the others are neutral or acidic.
🔋 Thermodynamics & Electrochemistry
Q54Which process has ΔS > 0?
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Correct: (C)
Sublimation (solid to gas) greatly increases molecular disorder.
Q55For a reaction with ΔH = -100 kJ and ΔS = -200 J/K, is it spontaneous at 298 K?
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Correct: (A)
ΔG = ΔH – TΔS = -100,000 – (298)(-200) = -40,400 J < 0, so spontaneous.
Q56What is E°cell for the Zn-Cu galvanic cell? (E°(Zn2+/Zn) = -0.76 V, E°(Cu2+/Cu) = +0.34 V)
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Correct: (D)
E°cell = E°cathode – E°anode = (+0.34) – (-0.76) = 1.10 V.
Q57What mass of Cu is deposited by a current of 1.00 A for 1.00 hour? (Cu2+ + 2e- → Cu)
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Correct: (A)
Charge = (1.00 A)(3600 s) = 3600 C; mol e- = 3600/96485 = 0.0373; mol Cu = 0.0187; mass = 0.0187 × 63.55 = 1.19 g.
Q58What is ΔG° for an electrochemical cell with n = 2 and E° = 1.10 V?
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Correct: (B)
ΔG° = -nFE° = -(2)(96485)(1.10) = -212,267 J ≈ -212 kJ.
☢ Nuclear & Descriptive Chemistry
Q59In the nuclear decay 238U92 → 234Th90 + X, what is particle X?
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Correct: (A)
Mass decreases by 4 and atomic number by 2, characteristic of alpha emission.
Q60Which ion gives a lilac (pale purple) flame test?
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Correct: (B)
K+ produces a characteristic lilac flame (Na+ is yellow, Ca2+ is orange-red, Cu2+ is green).
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