An approximate model of chemical equilibrium is formulated for modeling detonation processes in reacting gas mixtures. In comparison with exact (more detailed) models, this model uses additional physical assumptions allowing one not only to expand the scope of its application, but also to significantly simplify the form of the system of equations being solved. It is shown that for adequate (consistent with experiment) calculations of the gas dynamics of detonation flows, it is quite sufficient to describe the components of detonation products by a standard and limited set of substances. A procedure has been proposed to unambiguously determine the molar fractions of these substances in a state of chemical equilibrium, employing only the relative concentrations of atoms such as oxygen, carbon, hydrogen, nitrogen, and any other monatomic inert substances, such as argon.