AP Chemistry Practice Quiz: Reaction Mechanism and Rate Law
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Test your understanding with short quizzes. This quiz has 7 questions to check your progress.
Question 1 of 7
All Questions (7)
A) Rate = k[A][B]
B) Rate = k[C][D]
C) Rate = k[A][B][D]
D) Rate = k[E]
Correct Answer: A
According to the provided content, when the first step of a mechanism is the rate-limiting (slow) step, the overall rate law is determined by the molecularity of that step. The slow step involves one molecule of A and one molecule of B, so the rate law is Rate = k[A][B].
A) molecularity of the fastest step.
B) stoichiometry of the overall balanced reaction.
C) molecularity of the rate-limiting step.
D) concentration of the final products.
Correct Answer: C
The provided content explicitly states that for mechanisms where the first step is rate-limiting (slowest), the overall rate law is determined by the molecularity of that slowest step. This step acts as the bottleneck for the entire reaction.
A) Rate = k[NO₂]²[F₂]
B) Rate = k[NO₂][F]
C) Rate = k[NO₂][F₂]
D) Rate = k[NO₂F]
Correct Answer: C
The rate law is determined by the slowest step in the reaction mechanism. In this case, the slow step is Step 1: NO₂ + F₂ → NO₂F + F. The reactants in this elementary step are NO₂ and F₂. Therefore, the rate law is Rate = k[NO₂][F₂]. The rate law is not derived from the overall reaction stoichiometry.
A) Step 1: X + Y → Z (slow)
B) Step 1: 2X → W (slow)
C) Step 1: X → P (slow)
D) Step 1: Y + Y → Q (slow)
Correct Answer: B
The rate law is determined by the reactants of the slow step. A rate law of Rate = k[X]² indicates that the slow step has a molecularity involving two molecules of X. Mechanism B, where the slow step is 2X → W, is the only option that matches this requirement.
A) Rate = k[A]²[C]
B) Rate = k[B][C]
C) Rate = k[A]²
D) Rate = k[A][C]
Correct Answer: C
The overall rate law is determined by the molecularity of the slowest step. The slow step is Step 1, which involves two molecules of reactant A (2A → B). Therefore, the rate law is Rate = k[A]². The reactants from the fast step (C) and the intermediate (B) do not appear in the rate law derived from a slow first step.
A) Rate = k[O₃]²
B) Rate = k[O₃]
C) Rate = k[O₃][O]
D) Rate = k[O₂][O]
Correct Answer: B
The rate-determining step is the first step, which is labeled as slow. The molecularity of this step involves a single molecule of O₃. Therefore, the rate law for the overall reaction is first-order with respect to O₃, which is expressed as Rate = k[O₃].
A) The rate law is Rate = k[N₂O₄]² because it is the second step.
B) The rate law is Rate = k[N₂O₅] because the overall reaction is a decomposition.
C) The rate law is Rate = k[N₂O₅]² because the slow step involves two molecules of N₂O₅.
D) The rate law cannot be determined without experimental data.
Correct Answer: C
The overall rate law is determined by the molecularity of the rate-limiting (slow) step. Here, the slow step is Step 1, which involves the collision of two N₂O₅ molecules. Therefore, the rate law is second-order with respect to N₂O₅, written as Rate = k[N₂O₅]². The fast step does not influence the rate law.