MCAT General Chemistry Question 93: Answer and Explanation

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Question: 93

3. Pure sodium metal spontaneously combusts upon contact with room temperature water. What is true about the equilibrium constant of this combustion reaction at 25°C?

A. K_eq < 0
B. 0 < K_eq < 1
C. K_eq = 1
D. K_eq > 1

Correct Answer: D

Explanation:

Solve this question using the equation ΔG^°_rxn = -RT ln K_eq. ΔG_rxn^° is negative (as it must be for a spontaneous reaction), and R and T are always positive. Therefore, ln K_eq must also be positive for the sign convention to work out correctly. If ln K_eq > 0, then e^{ln K_eq} > e⁰ → K_eq > 1.

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