Definition of energy of activation (Arrhenius energy of activation; activation energy), Ea (SI unit: kJ mol-1)

1. An operationally defined quantity expressing the dependence of a rate constant on temperature according to

   Ea = RT2( ln k /T)p

   as derived from the "Arrhenius equation", k = A exp(-Ea/RT), where A (SI unit: as for the corresponding rate constant) is termed the "pre-exponential factor". See also enthalpy of activation.