Question

What is the EMF of a Cell?

Answer 1

1. An electrochemical cell is a device that converts chemical energy into electrical energy. Basically, it produces electricity from chemical reactions. Electrochemical cells are characterized by their voltage. This voltage depends on the nature of the chemical reactions occurring in the electrochemical cell.
2. An electrochemical cell consists of two metallic electrodes dipping in solutions of their respective metal ions.
3. When metal electrodes are dipped in a solution containing their metal ions, a potential difference is developed at the surface of the electrode. For example, when a Zinc ($\mathrm{Zn}$) rod is dipped in a solution of Zinc sulphate (${\mathrm{ZnSO}}_4$), the Zinc rod gets oxidised and Zinc ions (${\mathrm{Zn}}^{2+}$) from the rod pass into the solution leaving behind excess electrons on the surface of the rod.
   $\mathrm{Zn}\left(\mathrm{s}\right)\to {\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}$
   Thus, the Zinc rod gets negatively charged compared to the solution and a potential difference is set up at the Zinc electrode. This potential difference is called the Electrode Potential of the Zinc electrode.
4. The maximum potential difference that exists between the two electrodes of an electrochemical cell is its EMF. EMF stands for Electromotive Force.
5. Electrodes, where the electrode potential is set up by a reduction reaction, are called Cathodes and electrodes where the electrode potential is set up by an oxidation reaction are called Anodes. The EMF of a cell ($E_{cell}$) is calculated by subtracting the electrode potential of the anode ($E_{anode}$) from that of the cathode ($E_{cathode}$).
   $E_{cell}=E_{cathode}-E_{anode}$
6. EMF of a cell is the maximum potential difference between its electrodes.