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Given the standard electrode potentials Fe3+(aq) + e- -> Fe2+(aq), E° = 0.771 V and I2(g) + 2e- -> 2I-(aq), E° = 0.536 V, determine E°cell for the reaction 2Fe3+(aq) + 2I-(aq) -> 2Fe2+(aq) + I2(g).

1. (2 * 0.771 - 0.536) = 1.006 V
2. (0.771 - 0.5 * 0.536) = 0.503 V
3. 0.771 - 0.536 = 0.235 V
4. 0.536 - 0.771 = -0.235 V

Correct answer: 0.771 - 0.536 = 0.235 V

Solution

Cell potential is an intensive property and is independent of how many moles react. Therefore E°cell = E°(cathode) - E°(anode) = E°(Fe3+/Fe2+) - E°(I2/I-) = 0.771 - 0.536 = 0.235 V. The coefficients in the balanced equation never multiply the electrode potential.

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