[en] On the basis of a consistent set of photochemical kinetic equations previously obtained by the authors the effect of a resonant optical field on chemical equilibrium and on uni- and bimolecular chemical reaction kinetics is studied. We establish, in particular, the relationship between steady-state concentrations of reactants in a quasicontinuous light pulse field, that is, the generalized mass action law. Dependences of reaction product yields on the intensity of coherent light were found, also the relationships between effective reaction rate constants and coherent optical field parameters as well as relaxation interactions. The results are compared with those obtained from a phenomenological description widely used in practical photochemistry, based on elementary kinetics equations of balance type for reactant concentrations. It is shown that photochemical processes in coherent optical fields cannot be described correctly by rate (or balance) equations. (orig.)