Influence of the supporting electrolyte on standard electrode reaction rate constants on mercury

The influence of the nature and the concentration of the supporting electrolyte on standard reaction rate constants in non-aqueous solvents is discussed. Reductions of the monoatomic cations Zn2+, Cd2+ and Eu3+ as well as the reduction of bis(biphenyl)chromium(l) serve as models to evaluate the electrolyte contributions to standard reaction rate constants. The limitations of the Marcus theory and the Frumkin model to account for the effect of the electrolyte on standard reaction rate constants are described. The dependence of the apparent standard reaction rates on electrolyte properties such as the supporting electrolyte concentration, the viscosity and the resistivity are evaluated. Differences in the activities of the electroactive species at the reaction site and in the bulk of the solution are considered for qualitative descriptions of the electrolyte effect on standard reaction rates of Eu3+ on the one hand and of bis(biphenyl)chromium(l) on the other.