Cell Potential and Free Energy

Cell potential refers to the measure of the potential energy per unit of electric charge available from the oxidation/reduction reactions to drive the reaction from the reactants to the products.
It is represented by the letter E and expressed in volts (V).
The cell potential of an electrochemical cell is calculated as Ecell = Ecathode - Eanode.
A positive cell potential indicates a spontaneous reaction, while a negative cell potential indicates a non-spontaneous reaction.
The cell potential is influenced by the concentration of ions in the solution, temperature, and pressure.

The standard cell potential (E°cell) is the cell potential measured under standard conditions which are 25°C temperature, 1 atm pressure, and 1 M concentration of all reactants.
The standard cell potential directly relates to the strength of the reducing and oxidising agents. A stronger oxidising agent will have a more positive standard reduction potential.
The standard cell potential can also be determined from the standard reduction potentials of half-cells, using the formula E°cell = E°(cathode) - E°(anode).

Defined as the energy of a system that is available to do work, the Gibbs free energy (ΔG) is used to predict whether a chemical reaction will occur spontaneously or not.
It is quantified in joules (J) and can be calculated using the equation ΔG = ΔH - TΔS, where ΔH is the enthalpy change, T is the absolute temperature, and ΔS is the entropy change.
A negative Gibbs free energy change (ΔG < 0) indicates a spontaneous reaction and a system losing free energy.
A positive Gibbs free energy change (ΔG > 0) suggests a non-spontaneous reaction and a system gaining free energy.

There is a direct relationship between cell potential and Gibbs free energy. They both indicate whether a reaction is spontaneous or not.
The equation ΔG° = -nFE°cell is used to calculate the free energy change for a reaction. ‘n’ refers to the number of moles of electrons exchanged in the reaction and ‘F’ is the Faraday’s constant.
If a reaction has a positive E°cell and a negative ΔG°, it is spontaneous. Conversely, a negative E°cell and a positive ΔG° imply a non-spontaneous reaction.
Thus, aligning these two measures offers an invaluable tool in predicting the feasibility and spontaneity of a reaction.