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AP Chemistry 6.5 Energy of Phase Changes Questions

Practice AP Chemistry Unit 6.5 questions on calculating energy for heating, melting, freezing, vaporization, and condensation across phase transitions.

Syllabus
Effective Fall 2025
Course
AP Chemistry

Exam points

  • Use electrochemical equations and reduction potentials to analyze cell reactions, electron transfer, and direction.
  • Calculate cell voltage and relate electrode processes, charge balance, and stoichiometry to observed products.

Covered syllabus points

6.5.A—Explain changes in the heat q absorbed or released by a system undergoing a phase transition based on the amount…

Question 1

[Maximum number: 1]

A scientist is investigating the properties of a mixture of CH3OH\mathrm{CH}_{3} \mathrm{OH} and H2CO\mathrm{H}_{2} \mathrm{CO}. The scientist generates the following diagram to represent the mixture.

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

The scientist plans to cool a gaseous mixture of CH3OH\mathrm{CH}_{3} \mathrm{OH} and H2CO\mathrm{H}_{2} \mathrm{CO} to form a liquid mixture and finds data on the two compounds. The data are summarized in the table.

Table for Question 1 — AP Chemistry

The scientist analyzes the mixture after it is cooled and determines that 8.59 g of CH3OH(l)\mathrm{CH}_{3} \mathrm{OH}(l) is present. Calculate the amount of thermal energy, in kJ, that was removed to condense the 8.59 g of CH3OH\mathrm{CH}_{3} \mathrm{OH} (molar mass 32.04 g/mol32.04 \mathrm{~g} / \mathrm{mol} ) at its boiling point.

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