Electrochemical Equilibrium and Nernst Equation

The electrode potential for a general electrochemical reaction, as in Equation 1.78, is referred to the hydrogen electrode, whose reaction is given by Equation 1.79. 

Egq is related to the free energy of this reaction by the relation  

Applying Equations 1.76 and 1.77, one obtains the Nernst equation (Equations 1.82 and 1.83). 

Equation 1.83 simplifies if the SHE with p(H2) = 1 atm and a(H ) = 1 (molar scale) is used as a reference. E° the standard electrode potential is given by Equation 1.84. 

If we define the standard chemical potential or Gibbs free energy of a conventional electron by  

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