Dynamic properties of chemical reactions and appropriate relationships for open chemical equilibrium are discussed in approach of the chemical dynamics. New way to calculate composition of chemical systems in open equilibrium, based on the amended equation for the change of Gibbs' free energy, was exemplified using reactions of cobalt double oxides with sulfur. Evaluated this way equilibrium reaction extents had a good match with values found by direct thermodynamic simulation. The developed method allows us to perform analysis of complex chemical systems without coefficients of thermodynamic activity. In cases when the coefficients are in need or just desirable, the method offers a simple way to calculate them. Possible systems to apply method of chemical dynamics are discussed.