Name: Gibbs Free Energy, EMF and Equilibrium Constant
Uploaded: 2019-07-19
Duration: 6 min 15 s
Description: There are various thermodynamic parameters that are to be considered while studying the working of an electrochemical cell. Let's learn about them here!

Question

Explain the working of lead storage battery.

Accepted Answer

Lead storage cell is a storage cell which can operate both as voltaic cell and electrolytic cell. It is used in automobiles as a combination of six cells in series to form a battery with e.m.f equal to $12 V$ . This cell consists of lead grid packed with spongy lead which acts as anode and a grid of lead packed with lead oxide which acts as cathode. Aqueous solution of $H_{2} {SO}_{4}$ acts an electrolyte. The reactions that takes place at cathode and anode are;

At anode: $Pb (s) + {SO}_{4}^{2 -} (aq) \to {PbSO}_{4} (s)$ .

At cathode: ${PbO}_{2} (s) + 4 H^{+} (aq) + {SO}_{4}^{2 -} (aq) + 2 e^{-} \to {PbSO}_{4} (s) + 2 H_{2} O$ .

The overall reaction is: $Pb (s) + {PbO}_{2} (s) + 2 H_{2} {SO}_{4} (aq) \to 2 {PbSO}_{4} (s) + 2 H_{2} O$ .

In the given process, the lead sulphate is precipitated at both the electrodes. The voltage of each cell is about $2 V$ . The above process is for discharging the battery.

For recharging the battery: When both the electrodes are covered with lead sulphate the cell stops working as voltaic cell. In order to recharge the lead storage cell, it is connected to external source of direct current available from a generator. The positive pole of the generator is connected to the positive pole of the battery. It will reverse the flow of electrons. The reactions at anode and cathode are;

At cathode: ${PbSO}_{4} (s) + 2 e^{-} \to Pb (s) + {SO}_{4}^{2 -} (aq)$

At anode: ${PbSO}_{4} (s) + 2 H_{2} O \to {PbO}_{2} (s) + 4 H^{+} (aq) + {SO}_{4}^{2 -} (aq) + 2 e^{-}$

The overall reaction is: $2 {PbSO}_{4} (s) + 2 H_{2} O \to Pb (s) + {PbO}_{2} (s) + 2 H_{2} {SO}_{4} (aq)$ .

During charging process, the electrodes of the cell are restored to their original states.

Explain the working of lead storage battery.

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