What type of a battery is the lead storage battery 7 Write the anode and the cathode reactions and the overall reaction occurring in a lead storage battery when current is drawn from it.
(b) In the button cell, widely used in watches, the following reaction takes place :
`Zn(s) + Ag_(2)O (s) + H_(2)O (l) to Zn^(2+)(aq) + 2Ag (s) + 2OH^(-) (aq)`
Determine `E^(@)` and `DeltaG^(@)` for the reaction.
[Given: `E_(Ag^(+)//Ag)^(@) =+0.80 V, E_(Zn^(2+)//Zn)^(@) =-0.76 V]`

Explanation

Lead storage battery is a secondary cell.
Reactions at the anode and cathode when the current is drawn from it (discharge) are as follows :
At anode: `Pb(s) + SO_(4)^(2-) to PbSO_(4)(s) + 2e^(-)`
At cathode: `PbO_(2) (s) + 4H^(+)+ SO_(4)^(2-) to PbSO_(4) (s) + 2H_(2)O(l)`
Overall reaction: `Pb(s) + PbO_(2) (s) + 2H_(2)SO_(4) (aq) to 2PbSO_(4) + 2H_(2)O(l)`
(b) `Zn(s) + Ag_(2)O(s) + H_(2)O (l) to Zn^(2+) (aq) + 2Ag(s) + 2OH^(-) (aq)`
Given: `E_(Ag^(+)//Ag)^(@) = +0.80 V, E_(Zn^(2+)//Zn)^(@) = -0.76 V`
`E_("cell")^(@) = E_("cathode")^(@) -E_("anode")^(@)`
`=0.80 =-nFE^(@)`
`=-2 xx 96500 C mol^(-1) xx 1.56 V = -30180 J mol^(-1)`
`=-301.080 kJ mol^(-1)`