Question

What are chemical reactions taking place inside a lead accumulator when it supplied electric current to an external resistance?

Answer 1

Chemical Reaction for Discharging:

When the battery is discharged, it acts as a galvanic cell and the following chemical reaction occurs.

Negative:

$Pb\left(s\right)+HS{O_4}^{-}+H_{2}O\left(l\right)\to 2e^{-}+PbS{O}_4\left(s\right)+H_3{O}^{+}\left(aq\right)\left(oxidation\right)$

Positive:

$Pb{O}_2\left(s\right)+HS{O_4}^{-}\left(aq\right)+3H_3{O}^{+}\left(aq\right)+2e^{-}\to PbS{O}_4\left(s\right)+5H_{2}O\left(l\right)\left(reduction\right)$

1. Lead sulfate is formed at both the electrodes.
2. Two electrons are also transferred in the complete reaction.
3. The lead acid battery is packed in a thick rubber or plastic case to prevent leakage of the corrosive sulphuric acid.

Lead Acid Battery Charging:

1. The sulphuric acid existing in the lead discharge battery decomposes and needs to be replaced.
2. Sometimes, the plates change their structure by themselves.
3. Eventually, the battery becomes less efficient and should be charged or changed.

Chemical Reaction for Recharging:

The chemical reaction that takes place when the lead-acid battery is recharging can be found below:

Negative:

$2e^{-}+PbS{O}_4\left(s\right)+H_3{O}^{+}\left(aq\right)\to Pb\left(s\right)+HS{O_4}^{-}+H_{2}O\left(l\right)\left(reduction\right)$

Positive:

$PbS{O}_4\left(s\right)+5H_{2}O\left(l\right)\to Pb{O}_2\left(s\right)+HS{O_4}^{-}\left(aq\right)+3H_3{O}^{+}\left(aq\right)+2e^{-}\left(oxidation\right)$