Chemistry Department, Faculty of Science, Mansoura University, Egypt Manuscript received 24 September 1979, accepted 4 March 1980 A general equation for the variation of specific rate constant k with dielectric constant D for any reaction, in which the transition state may or may not be polarized and the slope of log k- D variation at any temperature may be positive or negative, has been proposed. This equalion was proved to be applicable to usual reactions as well as those exhibiting minima or maxima with solvent composition variation. The best method for computation of a\(\neq\), the distance of closest approach of solvent molecules to the transition state in a biomolecular reaction, has been developed. The acid hydrolysis of propionamide has been studied, in dioxane water solvent mixtures at five temperatures within the range 25-65°, in the light of !be proposed relations. The influence of the solvent on the reaction mechanism, which explains the kinetic data, has been quantitatively studied and discussed.