สมการอาร์เรเนียส
In 1889, Svante Arrhenius explained the variation of rate constants with temperature for several elementary reactions using the relationship
k = A exp(-Ea/RT)
where the rate constant k is the total frequency of collisions between reaction molecules A times the fraction of collisions exp(-Ea/RT) that have an energy that exceeds a threshold activation energy Ea at a temperature of T (in kelvins). R is the universal gas constant .