Relationship Between Potential, Gibbs Energy And Equilibrium Constant
The electrical work (electrical energy) is equal to the product of the EMF of the cell and electrical charge that flows through the external circuit i.e.,
......(i)
According to thermodynamics the free energy change 
is equal to the maximum work. In the cell work is done on the surroundings by which electrical energy flows through the external circuit, So
......(ii)
from eq. (i) and (ii) 
In standard conditions 
Where 
standard free energy change
But 
or 
