CHEM134 C003 LESSON 5: ADVANCED
CHEMICAL KINETICS AND
EQUILIBRIUM QUESTIONS AND
ANSWERS WITH VERIFIED SOLUTIONS
2026/2027 UPDATE. JUST RELEASED
1. For a third-order reaction involving a single reactant, what are the units of the rate
constant ‘k’ when time is in seconds and concentration is in Molarity?
A. M^-1 s^-1
B. M^-2 s^-1
C. s^-1
D. M s^-1
Answer: B
Conceptual Explanation: The unit for a rate constant is M(1-n)t-1. For n=3, it is M(1-3)s-1 =
M^-2 s^-1.
,2. Which of the following describes the relationship between the activation energy (Ea) and
the rate constant (k) according to the Arrhenius equation?
A. k increases exponentially as Ea increases.
B. k decreases exponentially as Ea increases.
C. k is independent of Ea at high temperatures.
D. k increases linearly as Ea decreases.
Answer: B
Conceptual Explanation: The Arrhenius equation is k = Ae^(-Ea/RT). Since Ea is in a
negative exponent, as Ea increases, the value of k decreases exponentially.
3. A first-order reaction has a half-life of 45.0 minutes. What percentage of the reactant
remains after 180.0 minutes?
A. 12.50%
B. 25.00%
C. 3.125%
D. 6.25%
Answer: D
Conceptual Explanation: 180 minutes is exactly 4 half-lives (180/45 = 4). The amount
remaining is (1/2)^4 = 1/16 = 6.25%.
, 4. In the reaction A + 2B -> C, if the rate law is Rate = k[A][B]^2, what happens to the rate if
the concentration of B is doubled while A is kept constant?
A. The rate increases by a factor of 4.
B. The rate doubles.
C. The rate increases by a factor of 8.
D. The rate remains unchanged.
Answer: A
Conceptual Explanation: Since the reaction is second order with respect to B, doubling [B]
results in a 2^2 = 4 fold increase in rate.
5. Which statement is true regarding the catalyst in a chemical reaction?
A. It increases the equilibrium constant K.
B. It provides an alternative pathway with a lower activation energy.
C. It increases the enthalpy change of the reaction.
D. It is consumed in the rate-determining step.
Answer: B
Conceptual Explanation: Catalysts speed up reactions by lowering the activation energy
through an alternative mechanism; they do not change the thermodynamics (K or delta H)
or get consumed overall.
CHEMICAL KINETICS AND
EQUILIBRIUM QUESTIONS AND
ANSWERS WITH VERIFIED SOLUTIONS
2026/2027 UPDATE. JUST RELEASED
1. For a third-order reaction involving a single reactant, what are the units of the rate
constant ‘k’ when time is in seconds and concentration is in Molarity?
A. M^-1 s^-1
B. M^-2 s^-1
C. s^-1
D. M s^-1
Answer: B
Conceptual Explanation: The unit for a rate constant is M(1-n)t-1. For n=3, it is M(1-3)s-1 =
M^-2 s^-1.
,2. Which of the following describes the relationship between the activation energy (Ea) and
the rate constant (k) according to the Arrhenius equation?
A. k increases exponentially as Ea increases.
B. k decreases exponentially as Ea increases.
C. k is independent of Ea at high temperatures.
D. k increases linearly as Ea decreases.
Answer: B
Conceptual Explanation: The Arrhenius equation is k = Ae^(-Ea/RT). Since Ea is in a
negative exponent, as Ea increases, the value of k decreases exponentially.
3. A first-order reaction has a half-life of 45.0 minutes. What percentage of the reactant
remains after 180.0 minutes?
A. 12.50%
B. 25.00%
C. 3.125%
D. 6.25%
Answer: D
Conceptual Explanation: 180 minutes is exactly 4 half-lives (180/45 = 4). The amount
remaining is (1/2)^4 = 1/16 = 6.25%.
, 4. In the reaction A + 2B -> C, if the rate law is Rate = k[A][B]^2, what happens to the rate if
the concentration of B is doubled while A is kept constant?
A. The rate increases by a factor of 4.
B. The rate doubles.
C. The rate increases by a factor of 8.
D. The rate remains unchanged.
Answer: A
Conceptual Explanation: Since the reaction is second order with respect to B, doubling [B]
results in a 2^2 = 4 fold increase in rate.
5. Which statement is true regarding the catalyst in a chemical reaction?
A. It increases the equilibrium constant K.
B. It provides an alternative pathway with a lower activation energy.
C. It increases the enthalpy change of the reaction.
D. It is consumed in the rate-determining step.
Answer: B
Conceptual Explanation: Catalysts speed up reactions by lowering the activation energy
through an alternative mechanism; they do not change the thermodynamics (K or delta H)
or get consumed overall.
