MCAT General Chemistry Question 176: Answer and Explanation
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Question: 176
11. Which of the following choices is indicative of a spontaneous reaction, assuming standard condition?
- A. E°cell is negative
- B. Q = Keq
- C. The cell is a concentration cell
- D. Keq > 1
Correct Answer: D
Explanation:
A spontaneous electrochemical reaction has a negative ΔG. Using the equation ΔG° = -RT ln Keq, Keq > 1 would result in ln Keq > 0, which means ΔG° < 0. A negative electromotive force, choice (A), or equilibrium state, choice (B), would not correspond to a spontaneous reaction. Concentration cells can be spontaneous; however, if the concentration cell had reached equilibrium, it would cease to be a spontaneous reaction, eliminating choice (C). When an answer choice may be true, but does not have to be—it is the wrong answer on Test Day.