In
chemistry,
activation energy is a term introduced in 1889 by the Swedish scientist
Svante Arrhenius to describe the minimum energy which must be available to a chemical system with potential reactants to result in a
chemical reaction. Activation energy may also be defined as the minimum energy required to start a chemical reaction. The activation energy of a reaction is usually denoted by
Ea and given in units of
kilojoules per mole (kJ/mol) or
kilocalories per mole (kcal/mol).