An equation for the average departure from equilibrium of a species is derived. This equation has a source term for the production of this non-equilibrium material due to the. mixing process. In some systems the chemical kinetic rate is proportional to a simple power of the departure from equilibrium and a perturbation analysis for this quantity is possible for large Damkohler number. The lead term in (his expansion is that formed by setting the mean kinetic rate equal to the source term for the rate of production of non-equilibrium material by mixing. Two systems of interest are examined in the light of this analysis. The ozone/NOxsystem of photochemical smog is found to have a Damkohler number near unity and full integration of the departure from equilibrium equation is indicated. For hydrogen/air diffusion flames the Damkohler number is reasonably high and estimates of the departure from equilibrium and the effect on nitric oxide formation are possible.
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