A reduction in the @R05156@ of certain reactions of a @S06082@ RX in solution [by a path that involves a @P04810@ with formation of R⁺ (or R⁻ ) ions as reaction intermediates] caused by the addition to the reaction mixture of an electrolyte solute containing the 'common ion' X⁻ (or X⁺). For example, the rate of @S05762@ of diphenylmethyl chloride in acetone-water is reduced by the addition of salts of the common ion Cl^- which causes a decrease in the @Q04999@ concentration of the diphenylmethyl @C00907@ in the scheme: This phenomenon is a direct consequence of the @M03725@ on @I03183@ equilibria in electrolytic solution. More generally, the common-ion effect is the influence of the 'common ion' on the reactivity due to the shift of the @D01801@ equilibrium. It may also lead to an enhancement of the @R05156@.