MCAT Physics Question 39: Answer and Explanation

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Test Information

Question: 39

9. A student making a coffee cup calorimeter fails to use a second coffee cup and incompletely seals the lid. What was her initial goal, and what was the result of this mistake?

  • A. She was trying to create an isolated system but created an open system instead.
  • B. She was trying to create an isolated system but created a closed system instead.
  • C. She was trying to create a closed system but created an open system instead.
  • D. She was trying to create a closed system but created an isolated system instead.

Correct Answer: B

Explanation:

Calorimeters are our best approximations of isolated systems, where neither energy nor matter is exchanged with the environment. By failing to use an insulating layer and failing to fully contain the system, heat can be exchanged with the environment and pressure may be dissipated. Because the question stem implies that the top was mostly secured, it is reasonable to believe that this now approximates a closed system and not an open system because matter is not exchanged with the environment.

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