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At 298 K, the standard free energies of formation (kJ mol⁻¹) of H2O(l), CO2(g), and pentane(g) are −237.2, −394.4, and −8.2, respectively. What is the standard cell potential, E°cell, for a pentane–oxygen fuel cell?

1. 1.968 V
2. 2.0968 V
3. 1.0968 V
4. 0.0968 V

Correct answer: 1.0968 V

Solution

Combustion: C5H12 + 8 O2 -> 5 CO2 + 6 H2O. delta G = [5(-394.4) + 6(-237.2)] - (-8.2) = -3387 kJ. Each O2 accepts 4 e-, so n = 32. E = 3387000/(32*96485) = 1.097 V.

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