Relation of emfs to thermodynamic quantities

Equation (8.14) corresponds to reversible changes where the only work done is w = —pAV. When the work done is also due to the passage of charge, —EAQ, it follows that 

Experiments on reversible cells are normally carried out at constant Tand p. 

An expression for AQ is needed, and this can be illustrated by reference to the redox reaction  

But to find the charge passed when this occurs it is necessary to write out the individual redox reactions showing the number of electrons, z, involved for the reaction with stoichiometry as written  

These equations are fundamental to the study of reversible cells (see Chapter 9). 

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