A galvanic cell is an electrochemical cell that converts the chemical energy of a spontaneous redox reaction into electrical energy. In this device the Gibbs energy of the spontaneous redox reaction is converted into electrical work which may be used for running a motor or other electrical gadgets like heater, fan, geyser, etc. Daniell cell is one such cell in which the following redox reaction occurs.

Zn(s) + Cu²⁺(aq) → Zn²⁺ (aq) + Cu(s)

This reaction is a combination of two half reactions whose addition gives the overall cell reaction:

(i) Cu²⁺ + 2e^– → Cu(s) (reduction half reaction) 

(ii) Zn(s) → Zn²⁺ + 2e^– (oxidation half reaction) 

These reactions occur in two different portions of the Daniell cell. The reduction half reaction occurs on the copper electrode while the oxidation half reaction occurs on the zinc electrode. These two portions of the cell are also called half-cells or redox couples. The copper electrode may be called the reduction half cell and the zinc electrode, the oxidation half-cell.

Which of the following is the correct representation of EMF of a cell?

E_cell = E_right - E_left 

The potential difference between the two electrodes of a galvanic cell is called the cell potential and is measured in volts. The cell potential is the difference between the electrode potentials (reduction potentials) of the cathode and anode. It is called the cell electromotive force (EMF) of the cell when no current is drawn through the cell.

E_cell = E_right – E_left