An approximate two- stage kinetic model of the chemical reaction in hydrogen- oxygen mixtures containing hydrogen peroxide, water, and inert diluents is developed. The model includes one differential equation for the calculation of the molar mass of the gas after the induction period and algebraic formulas for the calculation of the heat release, internal energy and thermodynamic parameters of the mixture. Based on this model, 2D numerical simulations of a multifront gas detonation wave are performed. These pioneering simulations correspond to the stoichiometric hydrogen- oxygen mixture with hydrogen peroxide and argon additions. An approximate model of chemical equilibrium in heterogeneous gas-condensed phase systems containing hydrogen peroxide is presented.