AP Chemistry Flashcards: Reaction Mechanism and Rate Law
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: June 2026
Review key ideas with interactive flashcards. This set includes 10 cards to help you master important concepts.
Based on the context, what does 'molecularity' refer to?
Molecularity refers to the number of reactant molecules that collide in an elementary step, which directly corresponds to the reaction orders in the rate law for that step.
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Based on the context, what does 'molecularity' refer to?
Molecularity refers to the number of reactant molecules that collide in an elementary step, which directly corresponds to the reaction orders in the rate law for that step.
What characteristic of the rate-limiting step determines the overall rate law?
The molecularity of the rate-limiting step determines the overall rate law for the reaction.
Why is the rate law for a multi-step reaction not determined by the overall balanced equation?
The rate law is determined by the slowest step in the reaction mechanism, not the stoichiometry of the overall reaction.
A reaction mechanism's first step is A + B → C (slow). What is the rate law for the overall reaction?
The rate law is determined by the reactants in the slow step, so the rate law is Rate = k[A][B].
If the first step of a reaction is 2X → Y (slow), what is the corresponding rate law?
Based on the molecularity of the slow step, the rate law for the overall reaction is Rate = k[X]².
The first step in a mechanism is A → Products (slow). What is the rate law?
Since the first step is slow and unimolecular, the rate law for the overall reaction is Rate = k[A].
Under what two conditions can the overall rate law be determined by the molecularity of the slowest step?
This applies when either each step in the mechanism is irreversible, or when the first step is the rate-limiting (slowest) step.
What is the rate-limiting step?
The rate-limiting step is the slowest elementary step in a reaction mechanism, which governs the overall rate of the reaction.
State the rule for identifying the rate law from a mechanism with a slow first step.
For a mechanism with a slow first step, the overall rate law is equivalent to the rate law for that first elementary step.
How is the overall rate law determined for a reaction mechanism where the first step is the slowest?
The overall rate law is determined by the molecularity of the slow, rate-limiting first step.