Diffusion rate of biologically important electrolytes through parchment‐supported silver chloride membrane have been determined by the use of Nernst‐Planck equation at various temperatures taking into account membrane resistance Rm, membrane potential Em, etc. The diffusion rates were found to be primarily dependent upon the difference in the hydration energies of the counterion in the external solution. On the basis of Eisenman‐Sherry theory the diffusion rate sequence of alkali metal cations point towards the weak field strengths of the fixed charge groups. The various thermodynamic parameters, namely, ΔH‡, ΔF‡, and ΔS‡ were evaluated. The values of ΔS‡ found to be negative, indicating that the diffusion is taking place with partial immobilization in the membrane phase. A formal relation between ΔHhydration, ΔFhydration, and ΔShydration of cations with the corresponding values of ΔH‡, ΔF‡, and ΔS‡ for diffusion was also found to exist for the investigated system.

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