AP Chemistry 6.5 A Explain Changes in the Heat Q Absorbed or Released By a System Undergoing a Phase Transition Based on the Amount Questions

Practice AP Chemistry questions on calculating energy for melting, freezing, vaporization, condensation, and heating across a phase transition.

Exam points

Explain how solution concentration and solute-solvent interactions determine measurable solution properties.
Apply molarity, dilution and stoichiometric relationships to calculate solution composition and changes.

[Maximum number: 1]

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

Figure for Question AP Chemistry 6.5 A Explain Changes in the Heat Q Absorbed or Released By a System Undergoing a Phase Transition Based on the Amount Questions question 1 — AP Chemistry

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

Table for Question AP Chemistry 6.5 A Explain Changes in the Heat Q Absorbed or Released By a System Undergoing a Phase Transition Based on the Amount Questions question 1 — AP Chemistry

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

(ii) For the correct calculated value:

Point 04

$8.59 \mathrm{~g} \mathrm{CH}_{3} \mathrm{OH} \times \frac{1 \mathrm{~mol} \mathrm{CH}_{3} \mathrm{OH}}{32.04 \mathrm{~g} \mathrm{CH}_{3} \mathrm{OH}} \times \frac{-37.6 \mathrm{~kJ}}{1 \mathrm{~mol} \mathrm{CH}_{3} \mathrm{OH}}=-10.1 \mathrm{~kJ}$ , so 10.1 kJ are removed.

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AP Chemistry 6.5 A Explain Changes in the Heat Q Absorbed or Released By a System Undergoing a Phase Transition Based on the Amount Questions question 1