Summarizing Rate Laws

Key Concepts and Summary

Rate laws provide a mathematical description of how changes in the concentration of a substance affect the rate of a chemical reaction. Rate laws are determined experimentally and cannot be predicted by reaction stoichiometry. The order of reaction describes how much a change in the concentration of each substance affects the overall rate, and the overall order of a reaction is the sum of the orders for each substance present in the reaction. Reaction orders are typically first order, second order, or zero order, but fractional and even negative orders are possible.

Glossary

method of initial rates

use of a more explicit algebraic method to determine the orders in a rate law

overall reaction order

sum of the reaction orders for each substance represented in the rate law

rate constant (k)

proportionality constant in the relationship between reaction rate and concentrations of reactants

rate law

(also, rate equation) mathematical equation showing the dependence of reaction rate on the rate constant and the concentration of one or more reactants

reaction order

value of an exponent in a rate law, expressed as an ordinal number (for example, zero order for 0, first order for 1, second order for 2, and so on)