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AP Chemistry 9.1: Entropy

Practice AP Chemistry questions on predicting the sign and relative size of entropy changes from particle dispersion, phase, temperature, and gas moles.

Syllabus
Effective Fall 2025
Course
AP Chemistry

Exam points

  • Explain how acid-base reactions involve proton transfer and conjugate pairs in solution.
  • Apply pH, pOH and equilibrium relationships to calculate concentrations and predict acid-base behavior.

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 9.1.A—Identify the sign and relative magnitude of the entropy change associated with chemical or physical processes question 1 — AP Chemistry
Figure for Question 9.1.A—Identify the sign and relative magnitude of the entropy change associated with chemical or physical processes 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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