Why is an external e.m.f of more than 2....

Why is an external e.m.f of more than `2.2V` required for the extraction of `Cl_(2)` from brine ?

Text Solution

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The oxidation reaction involved in the oxidation of `Cl^(-)` ions to `Cl_(2)` is :
`2Cl^(-)(aq)+2H_(2)O(l) to 2OH^(-)(aq)+H_(2)(g)+ Cl_(2)(g)`
The value of `DeltaG^(@)` for the reaction is `+422` kJ (standard value). The `E_("Cell")^(@)` can be calculated as,
`DeltaG^(@)=- nF E_("Cell")^(@) " or " E_("Cell")^(@)=- (DeltaG^(@))/(nF)`
`DeltaG^(@)=422 kJ =422000 J=422000 CV, n=2`
`E_("Cell")^(@)=-((422000 CV))/((2xx96500 C))=-2.19~~-2.20 V`
Since `E_("Cell")^(@)` comes out to be `-2.20` V for the electrolytic cell involving the oxidation of `Cl^(-)` ions, an external emf of more than `2.2` V is needed.

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