Combined diffusion coefficients in equilibrium mixtures of dissociating gases

It is shown that diffusion due to concentration and temperature gradients in a mixture of two nonreacting homonuclear gases consisting of arbitrarily many species in chemical equilibrium may be described by one ordinary and one thermal diffusion coefficient. These coefficients replace the 1/2q(q−1) independent ordinary diffusion coefficients and the q−1 independent thermal diffusion coefficients required in previous treatments to describe diffusion in a q-species gas mixture. A sample calculation for a mixture of dissociating nitrogen and oxygen is presented.