Ncert Exercises & Solutions

What is the relationship between Gibbs free energy of the cell reaction in a galvanic cell and the emf of the cell? When will the maximum work be obtained from a galvanic cell?

If concentration of all reacting speciesis unity, then E_cell = E⁰_cell and

∆

G⁰ = -nFE⁰_cell

where,

∆_{r}

G° is standard Gibbs energy of the reaction
E⁰_cell = emf of the cell
nF = charge passed

If we want to obtain maximum work from a galvanic cell then charge has to be passed reversibly.
The reversibly work done by a galvanic cell is equal to decrease in its Gibbs energy.

∆_{r}

G = — nFE⁰_cell

As E_cell is an intensive parameter but

∆_{r}

G is an extensive thermodynamic property and the value depends on n.

For reaction, Zn (s) + Cu²⁺ (aq)

\to

Zn²⁺ (aq) + Cu(s) in a galvanic cell,

∆_{r}

G = — nFE⁰_cell [Here, n = 2]

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