From Charged to Well-Defined Species The Electrochemical Equilibrium

From Charged to Well-Defined Species The Electrochemical Equilibrium 

The chemical potentials of charged species are not well-defined, and we need to represent them instead by chemical potentials of neutral species. For this purpose, we may assume equilibria between neutral and charged species and electrons, in the electrochemical redox reaction  

We may now insert this for all ionic species, n, in the expression for the electrical potential gradient. The entry (among k) for electrons is left unsubstituted. 

When required, we may substitute the chemical potential of the neutral species with activities and partial pressures. For isothermal conditions and for ideal gases we obtain  

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