Non-Markovian kinetic equations of the reversible monomolecular-bimolecular reactions of the type A+Breversible arrowC (at arbitrary ratio between A and B concentrations) derived earlier are used in the, calculation of kinetics on macroscopic. space-time scales. It is found that the kinetics of the systems with different structure of reactants is universal, and it is the direct generalization of the kinetic law of mass action of formal chemical kinetics. The analysis of the kinetics allows one to establish the time range of the applicability of the law of mass action. It is shown that beyond these limits the usual kinetic law of mass action becomes invalid, and correct description of the kinetics even in the most rough approximation calls for the non-Markovian corrections to usual kinetic laws. (C) 2004 American Institute of Physics.