(a) What type of battery is the lead storage battery? 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 taken place.
$Z n (s) + A g_{2} O (s) + H_{2} O (l) \to Z N^{2 +} (a q) + 2 (A g (s) + 2 O H^{-} (a q)$
Determine $E^{o}$ and $Δ G^{o}$ for the reaction (given: $E_{A g^{+} / A g}^{o} = + 0.80 V, E_{Z n^{2 +} / Z n}^{o} = - 0.76 V)$ .

Open in App

Solution

(a) A lead storage battery is a secondary cell so we can charge the battery by passing current directly. So, it can be reused.
At anode:
$P b + S O_{4}^{- 2} \to P b S O_{4} + 2 e^{-}$
At cathode:
$P b O_{2} + S O_{4}^{- 2} + 4 H^{+} + 2 e^{-} \to P b S O_{4} + 2 H_{2} O$
Overall reaction:
$P b + P b O_{2} + 2 S O_{4}^{- 2} + 4 H^{+} + 2 e^{-} \to P b S O_{4} + 2 H_{2} O$
(b) From the given reaction, it is known that zinc is oxidised and silver is reduced in the button cell.
The reactions occuring at the anode and cathode are:
Anode : $Z n_{(s)} ⟶ Z n_{(a q)}^{2 +} + 2 e^{-}$
Cathode : $A g_{2} O_{(s)} + H_{2} O_{(i)} + 2 e^{-} \to 2 A g_{(s)} + 2 O H_{(a q)}^{-}$
Now, $E_{c e l l}^{0} = E_{c a t h o d e}^{0} - E_{a n o d e}^{0}$
$= E_{A g^{+} / A g}^{0} - E_{Z n^{2 +} / Z n}^{0}$
$= 0.80 - (- 7.6)$
$= 1.56 V$
We know that
$Δ_{r} G^{0} = - n E^{0} F$
Here,
$n = 2$
$F = 96500 C m o l^{- 1}$
$Δ^{r} G^{0} = - 2 \times 1.56 \times 96500 J m o l^{- 1}$
$= - 301080 J m o l^{- 1}$

Suggest Corrections

Similar questions

Z n (s) + A g_{2} O (s) + H_{2} O (l) \to Z n^{2 +} (a q) + 2 A g (s) + 2 O H^{-} (a q)

Δ_{r} G^{θ}

E^{θ}

△ G^{\circ}

Z n (s) + A g_{2} O (s) + H_{2} O (l) ⇌ Z n^{2 +} (a q) + 2 A g (s) + 2 O H^{-} (a q)

E_{A g^{+} / A g}^{\circ} = + 0.80 V

E_{Z n^{2 +} / Z N}^{\circ} = - 0.76 V

Δ_{r} G^{o}

Z n_{(s)} + A g_{2} O_{(s)} + H_{2} O_{(l)} \to Z n_{(a q)}^{2 +} + 2 A g_{(s)} + 2 O H_{(a q)}^{-}

[E_{A g_{2} O / A g}^{o} = 0.344 V, E_{Z n^{2 +} / Z n}^{o} = - 0.76 V]

Z n (s) + A g_{2} O (s) + H_{2} O (l) ⇌ 2 A g (s) + Z n^{2 +} (a q) + 2 O H^{-} (a q)

Z n^{2 +} (a q) + 2 e^{-} \to Z n (s); E^{\circ} = - 0.76 V

A g_{2} O (s) + H_{2} O (l) + 2 e^{-} \to 2 A g (s) + 2 O H^{-} (a q), E^{\circ} = 0.34 V

Δ G

Z n_{(s)} + A g_{2} O_{(s)} + H_{2} O_{(l)} \to Z n_{(a q)}^{2 +} + 2 A g_{(s)} + 2 O H^{-}_{(a q)}

E_{{A g}^{+} / A g}^{0} = + 0.80 V

E_{{Z n}^{+ 2} / Z n}^{0} = - 0.76 V

Join BYJU'S Learning Program