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AP Chemistry 9.1 Introduction to Entropy Questions

Practice AP Chemistry Unit 9.1 questions on predicting entropy changes from particle dispersion, phase, temperature, and gas-particle changes.

Syllabus
Effective Fall 2025
Course
AP Chemistry

Covered syllabus points

9.1.A—Identify the sign and relative magnitude of the entropy change associated with chemical or physical processes

Question 1

[Maximum number: 1]

White phosphorus is composed of P4\mathrm{P}_{4} molecules with a tetrahedral structure, as shown in the diagram on the left. Each P atom is bonded to the other three P atoms by single bonds, as shown in the incomplete Lewis diagram on the right.

Figure for Question 1 — AP Chemistry
Figure for Question 1 — AP Chemistry

The reaction of white phosphorus with oxygen to form P4O10(s)\mathrm{P}_{4} \mathrm{O}_{10}(s) is thermodynamically favorable at 298 K. The reaction is represented by equation 1.

The entropy change of the reaction, ΔS∘\Delta S^{\circ}, is negative. Using particle-level reasoning, explain why the entropy decreases as the reaction progresses.

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