CHEM 120 Exam 3 Week 8 2026 – Units 5, 6, 7 | Complete Questions & Verified Answers | Chemistry Study Guide | Instant Download

CHEM 120 EXAM 3 WEEK 8 TOPICS (UNITS 5, 6, AND 7) |
QUESTIONS AND ANSWERS | VERIFIED ANSWERS PLUS
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1. Which factor does not affect the rate of a chemical reaction?
A) Temperature
B) Concentration of reactants
C) Presence of a catalyst
D) Color of the reactant
Answer: D – The color of a reactant does not influence reaction rate unless it absorbs
light in photochemical reactions.
2. The rate law for 2A + B → C is rate = k[A][B]^2. What is the overall order?
A) 1
B) 2
C) 3
D) 4
Answer: C – Overall order = sum of exponents: 1 + 2 = 3.
3. Doubling [A] in a first-order reaction will:
A) Double the rate
B) Quadruple the rate
C) Remain the same
D) Halve the rate
Answer: A – First-order reaction rate is directly proportional to [A].
4. The half-life of a first-order reaction depends on:
A) Initial concentration
B) Rate constant
C) Both A and B
D) None of the above
Answer: B – t½ = 0.693/k; independent of initial concentration.
5. A catalyst works by:
A) Increasing ΔH
B) Lowering activation energy
C) Shifting equilibrium
D) Being consumed
Answer: B – Catalysts lower activation energy, increasing reaction rate without being
consumed.
6. For a zero-order reaction, [A] vs. time is:
A) Exponential decay
B) Linear decrease
C) Quadratic decrease
D) Constant
Answer: B – [A] decreases linearly with time: [A] = [A]₀ – kt.
7. The Arrhenius equation relates:
A) Activation energy and rate constant

, B) Concentration and equilibrium constant
C) Pressure and temperature
D) Half-life and reaction order
Answer: A – k = Ae^(-Ea/RT) links rate constant k to activation energy Ea.
8. In a reaction mechanism, the slowest step:
A) Determines the rate law
B) Does not affect the rate
C) Occurs after all fast steps
D) Involves intermediates only
Answer: A – The slowest step is the rate-determining step.
9. Increasing temperature generally:
A) Decreases the rate constant
B) Has no effect
C) Increases the rate constant
D) Reverses the reaction
Answer: C – Higher temperature increases fraction of molecules exceeding Ea.
10. The unit of a second-order rate constant is:
A) s⁻¹
B) M⁻¹ s⁻¹
C) M s⁻¹
D) M² s⁻¹
Answer: B – For rate = k[A]^2, k has units M⁻¹ s⁻¹.
11. At equilibrium:
A) All reactants are converted to products
B) Forward and reverse reaction rates are equal
C) Only products are present
D) Concentrations are equal
Answer: B – At equilibrium, forward and reverse rates are equal.
12. For the reaction N₂ + 3H₂ ⇌ 2NH₃, increasing pressure favors:
A) Reactants
B) Products
C) No change
D) Depends on temperature
Answer: B – Higher pressure favors the side with fewer gas molecules.
13. Adding a catalyst to a reaction at equilibrium will:
A) Shift equilibrium to products
B) Shift equilibrium to reactants
C) Increase reaction rate without shifting equilibrium
D) Decrease reaction rate
Answer: C – Catalysts speed both forward and reverse reactions equally.
14. For an exothermic reaction, increasing temperature:
A) Increases K
B) Decreases K
C) Does not change K
D) Reverses the reaction
Answer: B – Higher temperature favors reactants in exothermic reactions.

,15. The reaction quotient Q is:
A) Equal to K only at equilibrium
B) Always greater than K
C) Always less than K
D) Unrelated to concentrations
Answer: A – Q = [products]/[reactants]; at equilibrium, Q = K.
16. Le Châtelier’s Principle predicts that adding reactant will:
A) Shift equilibrium toward reactants
B) Shift equilibrium toward products
C) Have no effect
D) Decrease reaction rate
Answer: B – Adding reactant shifts equilibrium to produce more products.
17. In heterogeneous equilibrium, pure solids and liquids:
A) Are included in K expression
B) Are not included
C) Affect Q but not K
D) Must be in excess
Answer: B – Concentrations of solids and liquids are constant.
18. Kc = 1.0 × 10⁻² indicates:
A) Products are favored
B) Reactants are favored
C) 50% completion
D) Cannot be predicted
Answer: B – K << 1 means reactants are favored.
19. Kp is used for:
A) Aqueous reactions
B) Gas-phase reactions
C) Solid reactions
D) All reactions
Answer: B – Kp uses partial pressures, for gases.
20. A Brønsted-Lowry acid is:
A) Electron pair donor
B) Proton donor
C) Proton acceptor
D) Electron pair acceptor
Answer: B – Acids donate protons (H⁺).
21. The conjugate base of H₂SO₄ is:
A) HSO₄⁻
B) SO₄²⁻
C) H₃SO₄⁺
D) OH⁻
Answer: A – Removing one proton gives HSO₄⁻.
22. Strong acids:
A) Partially dissociate
B) Fully dissociate
C) React slowly with bases

, D) Are weak electrolytes
Answer: B – Strong acids dissociate completely in water.
23. Which solution has the highest pH?
A) 0.1 M HCl
B) 0.1 M NaOH
C) 0.1 M CH₃COOH
D) 0.1 M NH₄Cl
Answer: B – Strong base produces highest pH.
24. The pH of 1 × 10⁻³ M HCl is:
A) 3
B) 2
C) 4
D) 5
Answer: A – pH = -log[H⁺] = 3.
25. Weak acid HA, Ka = 1 × 10⁻⁵, [HA] = 0.1 M. [H⁺] ≈
A) 1 × 10⁻³ M
B) 1 × 10⁻² M
C) 1 × 10⁻⁴ M
D) 0.1 M
Answer: A – [H⁺] = √(Ka × [HA]) ≈ 1×10⁻³.
26. The conjugate acid of NH₃ is:
A) NH₂⁻
B) NH₄⁺
C) OH⁻
D) NH₃⁻
Answer: B – Adding a proton forms NH₄⁺.
27. A buffer resists pH change because it contains:
A) Strong acid only
B) Strong base only
C) Weak acid and conjugate base
D) Water only
Answer: C – Neutralizes added H⁺ or OH⁻.
28. Adding 0.1 mol NaOH to 1 L of buffer (0.1 M CH₃COOH & 0.1 M CH₃COONa) will:
A) Increase pH significantly
B) Decrease pH significantly
C) Remain nearly constant
D) Become neutral
Answer: C – Buffer neutralizes small amount of base.
29. Lowest pKa among:
A) HCl
B) CH₃COOH
C) NH₄⁺
D) HF
Answer: A – Strong acids have lowest pKa.
30. The equilibrium constant for 2SO₂ + O₂ ⇌ 2SO₃, Kc >> 1, indicates:
A) Reactants favored