JEE Main & Advanced Chemistry Electrochemistry Cell Potential Or Emf Of The Cell

Cell Potential Or Emf Of The Cell

Category : JEE Main & Advanced

(1) “The difference in potentials of the two half – cells of a cell known as electromotive force (emf) of the cell or cell potential.”

The difference in potentials of the two half – cells of a cell arises due to the flow of electrons from anode to cathode and flow of current from cathode to anode.

\[Anode\underset{Flow\,\,of\,\,current}{\overset{Flow\,\,of\,\,electrons}{\longleftrightarrow}}Cathode\]

(2) The emf of the cell or cell potential can be calculated from the values of electrode potentials of two the half – cells constituting the cell. The following three methods are in use :

(i) When oxidation potential of anode and reduction potential of cathode are taken into account

\[E_{\text{cell}}^{0}=\] Oxidation potential of anode + Reduction potential of cathode \[=E_{\text{ox}}^{0}\,(\text{anode})+E_{\text{red}}^{\text{0}}(\text{cathode})\]

(ii) When reduction potentials of both electrodes are taken into account

\[=E_{\text{Cathode}}^{\text{0}}-E_{\text{Anode}}^{\text{0}}\]\[=E_{\text{right}}^{\text{o}}-E_{\text{left}}^{o}\]

(iii) When oxidation potentials of both electrodes are taken into account

\[E_{\text{cell}}^{o}=\] Oxidation potential of anode – Oxidation potential of cathode \[=E_{\text{ox}}^{0}(\text{anode})-E_{\text{ox}}^{0}(\text{cathode})\]      

(3) Difference between emf and potential difference

Emf Potential difference
It is the potential difference between two electrodes when no current is flowing in the circuit. It is the difference of the electrode potentials of the two electrodes when the cell is under operation.
It is the maximum voltage that the cell can deliver. It is always less then the maximum value of voltage which the cell can deliver.
It is responsible for the steady flow of current in the cell. It is not responsible for the steady flow of current in the cell.

(4) Cell EMF and the spontaneity of the reaction :         We know, \[\Delta G=-nF{{E}_{cell}}\]

Nature of reaction \[\Delta \mathbf{G(or}\,\Delta {{\mathbf{G}}^{\mathbf{o}}}\mathbf{)}\] \[{{\mathbf{E}}_{\mathbf{cell}}}\mathbf{(or}\,\mathbf{E}_{\mathbf{cell}}^{\mathbf{o}}\mathbf{)}\]
Spontaneous - +
Equilibrium 0 0
Non - spontaneous + -


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