MCAT General Chemistry Question 175: Answer and Explanation

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Question: 175

10. Which of the following expressions correctly describes the relationship between standard electromotive force and standard change in free energy?

  • A. ΔG° = -nF(E°red,anode - E°red,cathode)
  • B.
  • C.
  • D. ΔG° = nF(E°red,anode - E°red,cathode)

Correct Answer: D

Explanation:

There are only two equations involving standard change in free energy in electrochemical cells: ΔG° = -nFE°cell and ΔG° = -RT ln Keq. Substituting E°cell = E°red,cathode - E°red,anode into the first equation and distributing the negative sign gives choice (D). Choice (A) would be the opposite of ΔG°. Setting the two equations equal to each other, we get RT ln Keq = nFE°cell. Solving for E°cell, we get which is the opposite of choice (B). Choice (C) incorrectly solves the algebra.

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