Rate expression

Definition

A rate expression describes the rate of a chemical reaction in terms of the concentration of reactants. It shows how the rate depends on the concentrations of each reactant.

5 Must Know Facts For Your Next Test

1. The general form of a rate expression is $rate = k[A]^m[B]^n$, where $k$ is the rate constant, and $[A]$ and $[B]$ are the concentrations of the reactants.
2. The exponents $m$ and $n$ in the rate expression are called reaction orders and must be determined experimentally.
3. Rate expressions can provide insights into the mechanism of a chemical reaction.
4. Units for the rate constant $k$ depend on the overall order of the reaction.
5. A zero-order reaction has a rate that is independent of the concentration of reactants.

Review Questions

• What is a rate expression and what does it tell you about a chemical reaction?
• How do you determine the exponents (reaction orders) in a rate expression?
• Why is it important to know that units for the rate constant vary with different reaction orders?

Related terms

Rate Constant: A proportionality constant ($k$) in the rate equation that is specific to a particular reaction at a given temperature.

Reaction Order: The power to which a reactant concentration is raised in a rate law; it indicates how changes in concentration affect reaction rates.

Half-Life: The time required for half of a reactant to be consumed in a chemical reaction, often used to describe first-order reactions.