Ionic strength dependence of rate constants

For reactions of ions in solution, the variation of the activity coefficients with reagent concentrations is sometimes ignored or, more commonly, assumed to be held constant by carrying out the reaction in the presence of some inert electrolyte which is at a much higher concentration than that of the reactants. 

The kinetic effect of ionic strength can be illustrated for a bimolecular reaction of the following type  

The simplest relationship between the activity coefficients, Yj, and the ionic strength, p, is given by the Debye-Hiickel limiting law, which applies for p 0.01 M  

Many kinetic studies are done at ionic strengths beyond the range of applicability of the Debye-Hiickel limiting law. The law was extended by Debye and Hiickel to take into account the finite size of the itms to give Ok following relationship, that is applicable for p 0.1 M  

The ionic strength dependence of k is essentially a property of the rate law. Therefore, the ionic strength dependence seldom affords new mechanistic information unless the complete rate law cannot be determined. These equations more often are used to correct rate constants from one ionic strength to another for the purpose of rate constant comparison. Ionic strength effects have been used to estimate the charge at the active site in large biomolecules, but the theory is substantially changed because the size of the biomolecule violates basic assumptions of Debye-HUckel theory. 

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