A quasi-stationary model for dissociation, recombination and vibrational kinetics in expanding flows is presented. The model is based on strongly nonequilibrium vibrational distributions different from the Boltzmann and Treanor ones. Different mechanism of energy exchanges at low, middle and high vibrational levels is taken into account. The equations of nonequilibrium gas dynamics are derived and applied to nozzle flows of (N2,N) and (O2,O) gas mixtures. The gas parameters and vibrational distributions in the nozzle are computed and compared with the ones obtained using approximate models and the influence of kinetic models on flow parameters is investigated.