Q.Write the cell reaction and calculate the electrical work obtained from the following galvanic cell at standard condition: Mg | Mg2+(aq) || Ag+(aq) | Ag. [Given: E°(Mg2+/Mg) = -2.36 volt & E°(Ag+/Ag) = 0.80 volt.] (1+2)

Spontaneity of a cell reaction is decided by the sign of $\Delta G^{\circ}$ (equivalently, a positive $E^{\circ}_{cell}$).

For any cell reaction, the free energy change is related to the cell EMF by

$\Delta G^{\circ} = -nFE^{\circ}_{cell}$

where $n$ = number of electrons transferred and $F$ = Faraday constant (a positive quantity).

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An electrolytic cell runs a non-spontaneous redox reaction by forcing electrical energy into it, so its Gibbs free energy change is positive.

The relation between Gibbs free energy change and cell EMF is Delta-G = -nFEcell.

In an electrolytic cell, an external power source drives a reaction that would NOT occur on its own (non-spontaneous), i.e. Ecell (of the reaction being forced) is negative, so Delta-G = -nF(Ecell) works out to be POSITIVE. This is consistent with the reaction being non-spontaneous and requiring an external energy input to proceed …