Advanced Placement (AP) · Chemistry
Reaction Rates
Why it matters
Defining and measuring rate.
Advanced20m readingPrerequisite: None
What is a rate law in chemistry?
Short answer
A rate law is an equation that relates the rate of a reaction to the concentrations of its reactants, each raised to an experimentally determined power called its order. It has the form rate = k[A]^m[B]^n, where k is the rate constant. Rate laws are found from experiment, not from the balanced equation, and reveal information about the reaction mechanism.
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Frequently asked questions
- How is reaction order determined?
- Experimentally — by measuring how the rate changes when each reactant’s concentration is varied.
- Can you read the rate law from the balanced equation?
- No. Orders must be found by experiment; they are not the stoichiometric coefficients.