ACS General Chemistry Practice Test 3

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?

(A) Mg
(B) Al
(C) Na
(D) Si
Show Answer

Correct: (C)

Atomic radius decreases across a period; Na is furthest left in period 3, so it is largest.

Q2Which element has the highest first ionization energy?

(A) Cl
(B) F
(C) Br
(D) I
Show Answer

Correct: (B)

Ionization energy increases up a group and across a period; F is the smallest halogen with the most tightly held electrons.

Q3Which element has the most exothermic electron affinity?

(A) O
(B) S
(C) F
(D) Cl
Show Answer

Correct: (D)

Cl has the highest electron affinity; F is smaller but electron-electron repulsion in its compact 2p subshell reduces the energy released.

Q4The ions K+, Ca2+, Cl-, and S2- are all isoelectronic. Which has the smallest ionic radius?

(A) K+
(B) Ca2+
(C) Cl-
(D) S2-
Show Answer

Correct: (B)

All have 18 electrons; Ca2+ has the most protons (20), giving the greatest nuclear attraction and smallest radius.

Q5Which element has the largest second ionization energy (IE2)?

(A) Na
(B) Mg
(C) Al
(D) Si
Show Answer

Correct: (A)

Removing a second electron from Na disrupts the stable noble-gas configuration of Na+, requiring enormously more energy.

Q6Which element has the ground-state electron configuration [Ar]4s1 3d5?

(A) Mn
(B) Fe
(C) V
(D) Cr
Show Answer

Correct: (D)

Cr is the well-known exception; the half-filled 3d subshell plus half-filled 4s is more stable than [Ar]4s2 3d4.

🔬 Chemical Bonding & Molecular Geometry

Q7What is the molecular geometry of SF4?

(A) Tetrahedral
(B) Seesaw
(C) Trigonal pyramidal
(D) Square planar
Show Answer

Correct: (B)

S has 5 electron domains (4 bonds + 1 lone pair); the lone pair occupies an equatorial position, giving a seesaw shape.

Q8Which molecule is polar?

(A) CO2
(B) BF3
(C) NH3
(D) CH4
Show Answer

Correct: (C)

NH3 has a trigonal pyramidal geometry with a lone pair; the bond dipoles do not cancel, unlike the symmetric CO2, BF3, and CH4.

Q9What is the hybridization of the central atom in XeF4?

(A) sp3
(B) sp3d
(C) sp2
(D) sp3d2
Show Answer

Correct: (D)

Xe has 6 electron domains (4 bonds + 2 lone pairs), requiring six hybrid orbitals: sp3d2.

Q10What is the approximate H-O-H bond angle in water?

(A) 104.5°
(B) 180°
(C) 120°
(D) 109.5°
Show Answer

Correct: (A)

The two lone pairs compress the tetrahedral angle from 109.5° to about 104.5°.

Q11Which nitrogen-nitrogen bond is shortest?

(A) N-N single bond
(B) N-H bond
(C) N≡N triple bond
(D) N=N double bond
Show Answer

Correct: (C)

Bond length decreases as bond order increases; the triple bond is shortest.

Q12Which compound has the highest lattice energy?

(A) NaCl
(B) MgO
(C) KCl
(D) CaO
Show Answer

Correct: (B)

Lattice energy increases with ionic charge and decreases with ionic size; Mg2+ and O2- give the strongest attraction.

Q13What is the formal charge on the sulfur atom in SO3?

(A) +2
(B) +1
(C) 0
(D) -1
Show Answer

Correct: (C)

S has 6 valence electrons; in SO3 it owns 6 (no lone pairs, half of 12 bonding electrons), so 6 – 6 = 0.

🧪 Stoichiometry & Aqueous Reactions

Q14How many moles of O2 are required for the complete combustion of 2.0 mol of propane (C3H8)?

(A) 5.0 mol
(B) 8.0 mol
(C) 10.0 mol
(D) 12.0 mol
Show Answer

Correct: (C)

C3H8 + 5O2 → 3CO2 + 4H2O; 2.0 mol × 5 = 10.0 mol O2.

Q15In the reaction 2H2 + O2 → 2H2O, 3.0 g of H2 and 40 g of O2 are mixed. What mass of H2O can form?

(A) 18 g
(B) 27 g
(C) 36 g
(D) 54 g
Show Answer

Correct: (B)

3.0 g H2 = 1.5 mol; 40 g O2 = 1.25 mol. O2 needs 2.5 mol H2, but only 1.5 mol is available, so H2 limits; 1.5 mol H2O = 27 g.

Q16A reaction has a theoretical yield of 50.0 g and an actual yield of 40.0 g. What is the percent yield?

(A) 60%
(B) 70%
(C) 80%
(D) 90%
Show Answer

Correct: (C)

Percent yield = (40.0/50.0) × 100% = 80%.

Q17What is the molarity of a solution containing 0.50 mol of NaCl in 2.0 L of solution?

(A) 0.10 M
(B) 0.25 M
(C) 0.50 M
(D) 1.0 M
Show Answer

Correct: (B)

M = 0.50 mol / 2.0 L = 0.25 M.

Q18What is the concentration when 100 mL of 6.0 M HCl is diluted to 1.0 L?

(A) 0.60 M
(B) 0.30 M
(C) 1.2 M
(D) 6.0 M
Show Answer

Correct: (A)

M1V1 = M2V2; (6.0)(0.100) = M2(1.0); M2 = 0.60 M.

Q19What is the net ionic equation for the reaction of aqueous AgNO3 with aqueous NaCl?

(A) AgNO3 + Cl- → AgCl + NO3-
(B) Na+ + Cl- → NaCl
(C) Ag+ + NO3- → AgNO3
(D) Ag+ + Cl- → AgCl(s)
Show Answer

Correct: (D)

Na+ and NO3- are spectator ions; only Ag+ and Cl- form the precipitate.

Q20Which of the following is a strong electrolyte?

(A) NaCl
(B) CH3COOH
(C) C6H12O6
(D) NH3
Show Answer

Correct: (A)

NaCl dissociates completely in water; acetic acid and ammonia are weak electrolytes, glucose is a nonelectrolyte.

🌀 Gases & Intermolecular Forces

Q21What pressure is exerted by 1.0 mol of an ideal gas at 273 K in a 22.4 L container?

(A) 0.50 atm
(B) 2.0 atm
(C) 1.0 atm
(D) 4.0 atm
Show Answer

Correct: (C)

P = nRT/V = (1.0)(0.0821)(273)/22.4 = 1.0 atm.

Q22How much faster does H2 effuse than O2 at the same temperature?

(A) 2 times
(B) 4 times
(C) 8 times
(D) 16 times
Show Answer

Correct: (B)

Graham's law: rate(H2)/rate(O2) = √(32/2) = √16 = 4.

Q23Which alkane has the highest boiling point?

(A) CH4
(B) C2H6
(C) C3H8
(D) C4H10
Show Answer

Correct: (D)

London dispersion forces strengthen with molar mass and surface area; butane is largest.

Q24Which substance exhibits hydrogen bonding in the liquid phase?

(A) CH4
(B) H2
(C) NH3
(D) CO2
Show Answer

Correct: (C)

NH3 has H bonded to N, a highly electronegative atom with a lone pair; the others lack this combination.

Q25A gas mixture contains 0.30 atm N2, 0.20 atm O2, and 0.10 atm Ar. What is the total pressure?

(A) 0.60 atm
(B) 0.30 atm
(C) 0.45 atm
(D) 0.90 atm
Show Answer

Correct: (A)

Dalton's law: Ptotal = 0.30 + 0.20 + 0.10 = 0.60 atm.

🔥 Thermochemistry

Q26Using ΔHf° values (CH4: -75, CO2: -394, H2O(l): -286 kJ/mol), what is ΔH for CH4 + 2O2 → CO2 + 2H2O?

(A) -393 kJ/mol
(B) -891 kJ/mol
(C) -572 kJ/mol
(D) -75 kJ/mol
Show Answer

Correct: (B)

ΔH = [-394 + 2(-286)] – [-75] = -891 kJ/mol.

Q27Given: (1) C + O2 → CO2, ΔH = -394 kJ; (2) CO + 1/2O2 → CO2, ΔH = -283 kJ. What is ΔH for C + 1/2O2 → CO?

(A) -677 kJ
(B) +111 kJ
(C) -283 kJ
(D) -111 kJ
Show Answer

Correct: (D)

Subtract (2) from (1): ΔH = -394 – (-283) = -111 kJ.

Q28How much heat is absorbed when 100 g of water is heated from 20°C to 30°C (c = 4.18 J/g·°C)?

(A) 4.18 kJ
(B) 2.09 kJ
(C) 8.36 kJ
(D) 41.8 kJ
Show Answer

Correct: (A)

q = (100)(4.18)(10) = 4180 J = 4.18 kJ.

Q29Which process is exothermic?

(A) Melting ice
(B) Boiling water
(C) Condensation of steam
(D) Sublimation of dry ice
Show Answer

Correct: (C)

Condensation releases the heat of vaporization; the others absorb heat.

Q30Using bond enthalpies (H-H: 436, Cl-Cl: 242, H-Cl: 431 kJ/mol), estimate ΔH for H2 + Cl2 → 2HCl.

(A) -92 kJ
(B) +184 kJ
(C) -862 kJ
(D) -184 kJ
Show Answer

Correct: (D)

ΔH = (436 + 242) – 2(431) = 678 – 862 = -184 kJ.

Q31Which substance requires the most heat to raise 100 g by 10°C?

(A) Water (c = 4.18 J/g·°C)
(B) Aluminum (c = 0.90 J/g·°C)
(C) Iron (c = 0.45 J/g·°C)
(D) Copper (c = 0.38 J/g·°C)
Show Answer

Correct: (A)

Water has the highest specific heat capacity, so it absorbs the most energy per degree.

⚡ Quantum Theory & Electronic Structure

Q32Which type of electromagnetic radiation has the shortest wavelength?

(A) Radio waves
(B) Microwaves
(C) Visible light
(D) X-rays
Show Answer

Correct: (D)

Wavelength decreases as frequency and energy increase; X-rays are the most energetic listed.

Q33Which set of quantum numbers is allowed for an electron in an atom?

(A) n = 2, l = 2, ml = 0, ms = +1/2
(B) n = 3, l = 2, ml = -2, ms = -1/2
(C) n = 1, l = 1, ml = 0, ms = +1/2
(D) n = 4, l = 3, ml = 4, ms = +1/2
Show Answer

Correct: (B)

l must be less than n (rules out A and C), and |ml| cannot exceed l (rules out D).

Q34How many orbitals are in the n = 3 shell?

(A) 3
(B) 6
(C) 9
(D) 16
Show Answer

Correct: (C)

Number of orbitals = n² = 9 (one 3s, three 3p, five 3d).

Q35In the photoelectric effect, what increases the kinetic energy of the ejected electrons?

(A) Increasing the frequency of the light
(B) Increasing the intensity of the light
(C) Increasing the exposure time
(D) Decreasing the wavelength below threshold has no effect
Show Answer

Correct: (A)

Photon energy E = hν; higher frequency means more energetic photons and faster electrons. Intensity only changes the number of photons.




⏱ Chemical Kinetics

Q36For the reaction A + B → products, the following data were collected: Exp 1: [A]=0.10, [B]=0.10, rate=2.0×10-3; Exp 2: [A]=0.20, [B]=0.10, rate=4.0×10-3; Exp 3: [A]=0.10, [B]=0.20, rate=8.0×10-3. What is the rate law?

(A) rate = k[A][B]
(B) rate = k[A]²[B]
(C) rate = k[A][B]²
(D) rate = k[A]²[B]²
Show Answer

Correct: (C)

Doubling [A] doubles the rate (first order in A); doubling [B] quadruples the rate (second order in B).

Q37What are the units of the rate constant k for a reaction that is second order overall?

(A) M-1·s-1
(B) s-1
(C) M·s-1
(D) M-2·s-1
Show Answer

Correct: (A)

For rate (M/s) = k[M]², k must have units of M-1·s-1.

Q38A first-order reaction has k = 0.0693 s-1. What is its half-life?

(A) 5.0 s
(B) 10 s
(C) 20 s
(D) 69.3 s
Show Answer

Correct: (B)

t1/2 = 0.693/k = 0.693/0.0693 = 10 s.

Q39How does a catalyst increase the rate of a reaction?

(A) It increases the average kinetic energy of the reactants
(B) It shifts the equilibrium toward products
(C) It increases the temperature of the system
(D) It provides an alternative pathway with lower activation energy
Show Answer

Correct: (D)

A catalyst lowers Ea without being consumed; it does not change ΔH or the equilibrium position.

Q40Which change will NOT increase the rate of a gas-phase reaction?

(A) Increasing the temperature
(B) Increasing the reactant concentrations
(C) Adding a catalyst
(D) Increasing the volume of the container
Show Answer

Correct: (D)

Larger volume decreases gas concentrations, reducing collision frequency and slowing the reaction.

Q41Which statement about the Arrhenius equation is true?

(A) The rate constant increases exponentially with temperature
(B) The activation energy increases with temperature
(C) The rate constant is independent of temperature
(D) The frequency factor decreases with temperature
Show Answer

Correct: (A)

k = Ae-Ea/RT; as T rises, the exponent becomes less negative and k grows exponentially.

⇆ Chemical Equilibrium

Q42What is the Kc expression for N2(g) + 3H2(g) ⇌ 2NH3(g)?

(A) Kc = [NH3]² / ([N2][H2]³)
(B) Kc = [N2][H2] / [NH3]
(C) Kc = [NH3] / ([N2][H2]³)
(D) Kc = ([N2][H2]³) / [NH3]²
Show Answer

Correct: (A)

Kc = [products]coeff / [reactants]coeff = [NH3]²/([N2][H2]³).

Q43For N2 + 3H2 ⇌ 2NH3 + heat, which change increases the equilibrium yield of NH3?

(A) Increasing the temperature
(B) Decreasing the pressure
(C) Increasing the pressure
(D) Adding a catalyst
Show Answer

Correct: (C)

Higher pressure shifts equilibrium toward fewer gas moles (4 → 2), favoring NH3; a catalyst does not change the position.

Q44For the reaction 2NO2(g) ⇌ N2O4(g), what is the relationship between Kp and Kc?

(A) Kp = Kc
(B) Kp = Kc(RT)-1
(C) Kp = Kc(RT)
(D) Kp = Kc(RT)²
Show Answer

Correct: (B)

Kp = Kc(RT)Δn with Δn = 1 – 2 = -1, so Kp = Kc(RT)-1.

Q45For a reaction at equilibrium, if Q < K, which direction will the reaction shift?

(A) Toward reactants
(B) Toward products
(C) No shift; it is at equilibrium
(D) Toward the side with fewer moles
Show Answer

Correct: (B)

Q < K means reactants are in excess relative to equilibrium, so the reaction proceeds forward to make more products.

Q46For H2 + I2 ⇌ 2HI, initial [H2] = [I2] = 0.10 M and equilibrium [HI] = 0.16 M. What is Kc?

(A) 64
(B) 16
(C) 32
(D) 128
Show Answer

Correct: (A)

x = 0.080 M reacted; [H2] = [I2] = 0.020 M; Kc = (0.16)²/(0.020)(0.020) = 64.

Q47Which factor does NOT affect the position of a chemical equilibrium?

(A) Temperature
(B) Pressure (for gases)
(C) Concentration
(D) Catalyst
Show Answer

Correct: (D)

A catalyst speeds both forward and reverse reactions equally, so the equilibrium position is unchanged.

🧫 Acids, Bases & Buffers

Q48What is the pH of 0.010 M HCl?

(A) 1.00
(B) 2.00
(C) 3.00
(D) 12.0
Show Answer

Correct: (B)

HCl is a strong acid; [H+] = 0.010 M, so pH = -log(0.010) = 2.00.

Q49What is the pH of 0.010 M NaOH?

(A) 2.00
(B) 7.00
(C) 10.0
(D) 12.0
Show Answer

Correct: (D)

[OH-] = 0.010 M, pOH = 2.00, pH = 14.00 – 2.00 = 12.0.

Q50What is the conjugate acid of HPO42-?

(A) H2PO4-
(B) PO43-
(C) H3PO4
(D) H2O
Show Answer

Correct: (A)

Adding one proton to HPO42- gives H2PO4-.

Q51Which pair constitutes a buffer solution?

(A) HCl and NaCl
(B) NaOH and HCl
(C) CH3COOH and CH3COONa
(D) HNO3 and NaNO3
Show Answer

Correct: (C)

A buffer needs a weak acid and its conjugate base; CH3COOH/CH3COO- qualifies.

Q52The Ka of acetic acid is 1.8 × 10-5. What is its pKa?

(A) 4.74
(B) 2.74
(C) 9.26
(D) 14.0
Show Answer

Correct: (A)

pKa = -log(1.8 × 10-5) = 4.74.

Q53In a titration, 25.0 mL of 0.10 M NaOH neutralizes 25.0 mL of HCl. What is [HCl]?

(A) 0.050 M
(B) 0.20 M
(C) 0.025 M
(D) 0.10 M
Show Answer

Correct: (D)

Equal volumes at the equivalence point of a 1:1 strong acid-base titration mean equal concentrations.

🔋 Thermodynamics & Electrochemistry

Q54Which reaction has a positive ΔS?

(A) 2H2(g) + O2(g) → 2H2O(l)
(B) CaCO3(s) → CaO(s) + CO2(g)
(C) N2(g) + 3H2(g) → 2NH3(g)
(D) H2O(l) → H2O(s)
Show Answer

Correct: (B)

A gas is produced from a solid, increasing disorder; the others decrease gas moles or freeze a liquid.

Q55For a reaction with ΔH = -100 kJ and ΔS = -200 J/K at 298 K, what is ΔG and is the reaction spontaneous?

(A) ΔG = -40.4 kJ; spontaneous
(B) ΔG = +40.4 kJ; nonspontaneous
(C) ΔG = -159.6 kJ; spontaneous
(D) ΔG = 0; at equilibrium
Show Answer

Correct: (A)

ΔG = -100,000 – (298)(-200) = -40,400 J = -40.4 kJ; negative ΔG means spontaneous.

Q56What is the standard cell potential for Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)? (E°: Cu2+/Cu = +0.34 V, Zn2+/Zn = -0.76 V)

(A) -1.10 V
(B) -0.42 V
(C) +1.10 V
(D) +0.42 V
Show Answer

Correct: (C)

E°cell = E°cathode – E°anode = 0.34 – (-0.76) = 1.10 V.

Q57Which species is the strongest oxidizing agent? (E°: F2 = +2.87, Cl2 = +1.36, Br2 = +1.07, I2 = +0.54 V)

(A) I2
(B) Br2
(C) Cl2
(D) F2
Show Answer

Correct: (D)

The strongest oxidizing agent has the most positive reduction potential: F2.

Q58In a galvanic cell, which statement is true?

(A) Oxidation occurs at the anode, which is negative
(B) Reduction occurs at the anode, which is positive
(C) Oxidation occurs at the cathode, which is negative
(D) Electrons flow from cathode to anode
Show Answer

Correct: (A)

Oxidation always occurs at the anode; in a galvanic cell the anode is the negative electrode and electrons flow anode → cathode.

☢ Nuclear & Descriptive Chemistry

Q59In the alpha decay of uranium-238, what particle is emitted?

(A) A beta particle
(B) An alpha particle (He-4 nucleus)
(C) A gamma ray only
(D) A neutron
Show Answer

Correct: (B)

Alpha decay emits a He-4 nucleus (238U → 234Th + 4He).

Q60Which oxide forms an acidic solution when dissolved in water?

(A) Na2O
(B) MgO
(C) SO3
(D) CaO
Show Answer

Correct: (C)

Nonmetal oxides like SO3 form acids (H2SO4); Na2O, MgO, and CaO are basic oxides.