Activity Coefficient. In Ideal Solutions chemical reactions and interactions between primary interactants are normally related to some function of the concentrations of the interactants. This simple relationship usually occurs at very low concentrations. However, at higher concentrations secondary interactions occur and the simple use of concentration no longer applies. This problem arises significantly when dealing with electrolytes. As a consequence, the interactant concentration value must be replaced by the interactant ‘activity’ which is defined as the product of the concentration and the interactant ‘activity coefficient’ (γ). In electrochemistry the value for the ‘activity coefficient’ (γ) is usually calculated from the Debye and Hückel Equation.

Further Information on this Topic can be found in the books of R.P.W. Scott by following the listed links