A quantum mechanical theory of nonadiabatic dissociative electron transfer processes in polar media is presented. Expressions for the transition probability in quantum and classical limits are derived for different model molecular potentials. It is shown that in the quantum limit the dependence of the transition probability on the dissociation energy of the chemical bond to be broken is involved in the temperature independent tunneling factor, whereas in the classical limit it comes from the activation free energy. Quantum effects lead to a weaker dependence on the reaction free energy as compared lo that for the purely classical case. Simple equations for activation free energy as a function of the free energy of the reaction are obtained in the classical limit, which generalizes earlier results.