Establish the relation between Gibbs free energy change and EMF of a cell
The relation between change in free energy and EMF is based on the fact that the electrical work done by an electrochemical cell is equal to the change in Gibbs free energy for the redox reaction occurring in the cell.
Electrical work done by the cell when 'n' moles of electrons are transferred through a potential difference Ecell is given-
Work = nFEcell
For a spontaneous reaction occurring in the cell, the maximum work that can be obtained is equal to the decrease in Gibbs free energy-
ΔG = −Work
Combining the above two equations, we get-
ΔG = −nFEcell
From this equation, If the Gibbs free energy change for a reaction is known, the EMF of the cell can be easily calculated and vice-versa.
Conditions:
1. If ΔG is negative the cell reaction occur spontaneously.
2. If ΔG is positive the cell reaction is not possible.
3. If ΔG is zero the cell reaction is in equilibrium.
