The theoretical efficiency of a hypothetical cell is about 84% which involves the following reaction A(s) + B^2+(aq) - A^2+(aq) + B(s); ΔH = –285 kJ, then, the standard EMF of the cell is

Question

The theoretical efficiency of a hypothetical cell is about 84% which involves the following reaction A(s) + B^2+(aq) -> A^2+(aq) + B(s); ΔH = –285 kJ, then, the standard EMF of the cell is

Prashant Kotian · Accepted Answer

Correct answer: B. Thermodynamic efficiency of a fuel cell is given by η = ΔG / ΔH. We have 0.84 = ΔG / (-285 kJ), so ΔG = -239.4 kJ = -239400 J. Using ΔG = -nFE°, where n = 2 for the transfer of 2 electrons, we get -239400 = -2 * 96500 * E°. Thus, E° = 239400 / 193000 = 1.24 V. Therefore, correct answer is B.

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