(a) Calculate ΔG° for the reaction $$\mathrm{Zn(s)+Cu^{2+}(aq)\longrightarrow Zn^{2+}(aq)+Cu(s)}$$ Given: E° for Zn$^{2+}$/Zn = −0.76 V, E° for Cu$^{2+}$/Cu = +0.34 V, R = 8.314 J K$^{-1}$ mol$^{-1}$, F = 96500 C mol$^{-1}$. (b) Give two advantages of fuel cells.

CBSE Class 12 · 2020 · Redox Reactions and ElectrochemistryLong Answer

(a) Calculate ΔG° for the reaction

Zn (s) + C u^{2 +} (aq) ⟶ Z n^{2 +} (aq) + Cu (s)

Given: E° for Zn

^{2 +}

/Zn = −0.76 V, E° for Cu

^{2 +}

/Cu = +0.34 V, R = 8.314 J K

^{- 1}

mol

^{- 1}

, F = 96500 C mol

^{- 1}

.
(b) Give two advantages of fuel cells.

Answer: (a) ΔG° ≈ −212.3 kJ mol⁻¹ (b) High efficiency; pollution-free (water as the only product) / continuous operation.

Solution

(a)

E_{ce l l}^{\circ} = 0.34 - (- 0.76) = 1.10 V, n = 2

Δ G^{\circ} = - n F E_{ce l l}^{\circ} = - 2 \times 96500 \times 1.10

Δ G^{\circ} = - 2.123 \times 1 0^{5} J = - 212.3 kJ mo l^{- 1}

(b) Advantages of fuel cells: (i) very high efficiency of energy conversion (~70%, against ~40% for thermal plants); (ii) pollution-free operation — in the H

_{2}

–O

_{2}

cell the only product is water (and they run continuously as long as fuel is supplied).

CBSE Class 12 Board · 2020 · Subjective

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CBSE Class 12 · 2020 · Redox Reactions and ElectrochemistryLong Answer

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