Question
Write the electrode reactions when lead storage cell generates electricity. What are the anode and cathode and the electrode reactions during its recharging?
✓
Answer
Recharging of the cell : When the discharged battery is connected to external electric source and a higher external potential is applied the cell reaction gets reversed generating $H_2SO_4$.
Reduction at the – ve electrode or cathode :$PbSO _{4( s )}+2 e ^{-} \rightarrow Pb ^{(s)}+ SO _{4( aq )}^{2-}$
Oxidation at the + ve electrode or anode :
$PbSO _4^{( s )}+2 H _{2( (1) } O \rightarrow PbO _2^{( s )}+4 H _{( aq )}^{+}+ SO _{4( aq )}^{2-}+2 e ^{-}$
The net reaction during charging is
$2 PbSO _{4(3)}+2 H _2 O _{( i )} \rightarrow Pb _{( s )}+ PbO _{2( s )}+4 H _{( aq )}^{+}+2 SO _{4( aq )}^{2-}$
$O R$
$2 PbSO _4^{(s)}+2 H _2 O \rightarrow Pb (s)+ PbO _{2^{(s)}}+2 H _2 SO _{4(\text { (aq) }}$
The emf of the accumulator depends only on the concentration of $H_2SO_4$.
Reduction at the – ve electrode or cathode :$PbSO _{4( s )}+2 e ^{-} \rightarrow Pb ^{(s)}+ SO _{4( aq )}^{2-}$
Oxidation at the + ve electrode or anode :
$PbSO _4^{( s )}+2 H _{2( (1) } O \rightarrow PbO _2^{( s )}+4 H _{( aq )}^{+}+ SO _{4( aq )}^{2-}+2 e ^{-}$
The net reaction during charging is
$2 PbSO _{4(3)}+2 H _2 O _{( i )} \rightarrow Pb _{( s )}+ PbO _{2( s )}+4 H _{( aq )}^{+}+2 SO _{4( aq )}^{2-}$
$O R$
$2 PbSO _4^{(s)}+2 H _2 O \rightarrow Pb (s)+ PbO _{2^{(s)}}+2 H _2 SO _{4(\text { (aq) }}$
The emf of the accumulator depends only on the concentration of $H_2SO_4$.
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