Equilibrium Constant of a Redox Chemical Reaction

Cell emf values and electrode potentials are important, not only because they are significant electroanalytically, but more because they can give information about possible chemical reactions and their equilibria. Equilibrium constants can be calculated by use of either cell emf values or electrode potentials. 

Calculation of equilibrium constant from emf of a cell The equilibrium constant of a chemical reaction can be calculated from the standard free-energy change by the equation 

For a spontaneous reaction, AG° is negative and, correspondingly, the equilibrium constant is greater than unity. With numerical values of RT and F at 25°C and conversion to logarithms of base 10, 

2Fe(III) + Sn(II) 2Feai) + Sn(IV) (12-37) Then consider the (hypothetical) cell with all ions at unit activity, 

This large value of the equilibrium constant indicates that the chemical reaction goes essentially to completion to the right as written. 

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