The Arrhenius activation energy for the reaction A + A leftrightarrows B + B in a dilute gas is calculated from a temperature dependence of the rate constant obtained from the perturbation solution of the Boltzmann equation. The first and the second approximation to the velocity distribution function are used in an analysis of nonequilibrium effects. Results obtained for the line-of-centers model and the Prigogine--Xhrouet model of reactive differential cross sections are presented. The Arrhenius activation energy is represented as a function of appropriate threshold energies.

PACS numbers: 05.20.Dd, 82.20.--w, 82.20.Mj, 82.20.Wt