Regents Chemistry Exam June 2024 Question 42
42 The graph below shows a compound being cooled, beginning in the liquid phase.
Which statement describes the average kinetic energy and the potential energy between minute 2 and minute 6?
(1) Average kinetic energy and potential energy both decrease.
(2) Average kinetic energy and potential energy both remain constant.
(3) Average kinetic energy remains constant and potential energy increases.
(4) Average kinetic energy remains constant and potential energy decreases.
Solution:
In a cooling curve, when the line is slanted, kinetic energy decreases (because temperature is decreasing) and potential energy stays the same. When the line is straight horizontally, potential energy decreases and kinetic energy stays the same. Between minute 2 and minute 6 we see a horizontal line which means potential energy decreases and kinetic energy remains constants. Choice 4 is the correct answer.
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