An equation relating the rate constant of a chemical reaction and the temperature at which the reaction is taking place:

k = Aexp(–Ea/RT)

where A is a constant, k the rate constant, T the thermodynamic temperature in kelvins, R the gas constant, and Ea the activation energy of the reaction. Reactions proceed at different rates at different temperatures, i.e. the magnitude of the rate constant is temperature dependent.

The Arrhenius equation is often written in a logarithmic form, i.e.

logek = logeA – E/2.3RT

This equation enables the activation energy for a reaction to be determined. The equation is named for the Swedish physical chemist Svante August Arrhenius (1859–1927).