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The standard e.m.f. of a galvanic cell involving cell reaction with n = 2 is found to be 0.295 V at 25°C. The equilibrium constant of the reaction would be (Given F = 96500 C mol–1; R = 8.314 J K–1 mol–1)

1. 2.0 × 10^11
2. 4.0 × 10^12
3. 1.0 × 10^2
4. 1.0 × 10^10

Correct answer: 2.0 × 10^11

Solution

The relationship between the equilibrium constant (K) and the standard e.m.f. (E°) is given by the Nernst equation: E° = (RT/nF)lnK. Substituting the values (R = 8.314 J K⁻¹ mol⁻¹, T = 298 K, n = 2, F = 96500 C mol⁻¹, E° = 0.295 V), we calculate lnK = (0.295 × 2 × 96500) / (8.314 × 298). Solving gives lnK ≈ 26.7, and K ≈ e^(26.7) ≈ 2.0 × 10¹¹.

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