An experimental and theoretical study has been made on chemical nonequilibrium flows in a supersonic nozzle for a mixture of dissociated gases and inert diluent. In the calculations, four different flow behaviors were assumed: one-dimensional non-equilibrium, two-dimensional nonequilibrium, two-dimensional equilibrium, and two-dimensional frozen flows. These were compared with measurements of the static pressure and NO2 concentration in the supersonic nozzle flow of the NO2-N4O2-N2 reactive system. Relatively good agreement demonstrates the applicability of the proposed calculation methods and the validity of the assumed reaction mechanisms and their rate constants.