The fundamental approach to the description of the kinetics of chemical reactions has been considered, and principle of chemical reaction independence and active mass law have been taken into account. Models for rate constants of elementary reaction have been discussed on the basis of the collision theory, the theory of activated complex, and the theory which takes into account the movement of intermediate particles to the reaction barrier. The collision theory is suggested for use at high temperatures, the theory of activated complex is recommended for application at moderate temperatures, and the theory which takes into account the movement of intermediate particle to the reaction barrier is relevant to low temperatures. It is emphasized that the principle of maximal change of free energy, which was suggested earlier, may be applied for analysis of the mechanism of chemical processes.