MCAT General Chemistry Question 198: Answer and Explanation
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Question: 198
2. Lyophilization would most likely be employed industrially in which of the following separations?
- A. Decreasing volume
- B. Increasing temperature
- C. Decreasing temperature
- D. The reaction will always be nonspontaneous.
Correct Answer: B
Explanation:
B Choice A is eliminated because decreasing volume would cause an increase in pressure, which would inhibit the transformation of a liquid to a gas. The question alludes that the process has a positive ∆H. Since the reaction involves changing two moles of liquid to three moles of gas, entropy increases so it will have a positive ∆S. Using the equation ∆G = ∆H T∆S, a reaction with a positive ∆H and ∆S will be spontaneous only at high enough temperatures. Therefore, choices C and D can be eliminated, making choice B correct.