EMF or cell Potential of a cell: The difference between the electrode potentials of the two electrodes constituting an electrochemical cell is known as electromotive force (emf) or cell potential of a cell. This acts as a driving force for the cell reaction. The potential difference is expressed in volts. Thus,
e.m.f = Ecathode – E anode
Since, in the representation of an electrochemical cell as a convention, cathode is written on right hand side and anode on the left hand side. Therefore, e.m.f. of a cell may also be written as – E cell = E Right – E Left
Therefore, e.m.f. of a cell may be defined as the potential difference between two electrodes of the cell when either no or negligible current is allowed to flow in the circuit. For example, the e.m.f. of a Daniell cell in which the concentrations of aqueous solutions of CuSO4 and ZnSO4 in the two half cells is 1M at 298 K is 1.10 volts.