Abstract: According to the Free-Energy Functions the following approximate formula without heat capacity for equilibrium constant is suggested:lgK_p= - (△H₂₉₈⁰/4.576T)+ (△S₂₉₈⁰/4.576)+a(T-298) where a = constant, obtained by use of only a single measurement of K_p.More than₁₁₀ equilibrium constants of reactions have been calculated at different temperatures and the results obtained coincide very well with the experimental values.