Equations are formulated for determining conditions in a chemically reacting gas situated inside an optical laser cavity. During lasing, the gain is held constant throughout the cavity as determined by a gain-equals-loss condition. For each vibrational level, a Boltzmann distribution for the rotational levels is assumed with lasing on each vibrational band at line center of the transition that has maximum gain. The final system consists of flow, chemical rate, and gain-equals-loss equations. Special numerical procedures for solving this system of coupled, nonlinear equations are described.