The role of nonequilibrium effects on negative Arrhenius activation energy in a Lorentz gas

The perturbation method is used for solving the Boltzmann equation for a reactive Lorentz gas for the chemical reaction A+B → products. Analytical equations for the Arrhenius activation energy EA are derived for the reversed Prigogine–Xhrouet and reversed line-of-centers models. The results are compared with numerical results obtained by Stiller et al. from the Lorentz–Fokker–Planck equation. It is confirmed that the nonequilibrium effects can enlarge small negative values of EA for reactions in which only the molecules colliding with small relative velocities can react. If EA=0 in the nonequilibrium description the temperature of the system equals the Shizgal–Karplus temperature.