Empirical evidence is given to show that individual ion activity coefficients can be written as logggr;t=Zt2G(S)+ngr;1agr;1t+ngr;2agr;2tC, where ngr;1and ngr;2are the number of ions of type 1 and 2 formed from one formula of the supporting electrolyte,Cis the formal concentration of the electrolyte,Ztis the charge of the iont,G(S) is a function of the medium only, agr;1tis a function of the ionhyphen;size parameter for ions 1 andt, and agr;2tis a similar function of the ions 2 andt. The equation is applicable only if the concentration of iontis small in comparison to the concentration of electrolyte. Mayer's theory predicts that the above equation, when used to calculate experimentally observable quantities, should be correct to within good accuracy for ionhyphen;size parameters between 5.5 and 8.5 Aring; in a 1ndash;1 supporting electrolyte and for higherhyphen;charged electrolytes at ionic strengths above about 0.2. Using this equation one can calculate the ratio of the rate constant for the bromacetatemdash;thiosulfate reaction to that for the peroxydisulfatemdash;iodide reaction at infinite dilution from data obtained in MgSO4, Mg(NO3)2, Na2SO4, and NaNO3solutions at concentrations between 0.25 and 2F. The value obtained under these conditions is within experimental accuracy of the value obtained by extrapolation to infinite dilution from ionic strengths below 0.02.
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