---
title: "A student conducts an experiment to compare the thermal energy required for phase changes of water, \\(\\text{H}_2\\text{O}\\). The student measures the thermal energy required to completely melt a \\(18.0 \\text{ g}\\) sample of ice at \\(0^\\circ\\text{C}\\) (\\(q_{\\text{fus}}\\)) and the thermal energy required to completely vaporize a \\(18.0 \\text{ g}\\) sample of liquid water at \\(100^\\circ\\text{C}\\) (\\(q_{\\text{vap}}\\)). Which of the following correctly compares \\(q_{\\text{vap}}\\) to \\(q_{\\text{fus}}\\) and provides the correct molecular explanation?"
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url: "https://nerd-notes.com/ubq/119321/"
date_modified: "2026-08-19T12:39:49+00:00"
---

# A student conducts an experiment to compare the thermal energy required for phase changes of water, \(\text{H}_2\text{O}\). The student measures the thermal energy required to completely melt a \(18.0 \text{ g}\) sample of ice at \(0^\circ\text{C}\) (\(q_{\text{fus}}\)) and the thermal energy required to completely vaporize a \(18.0 \text{ g}\) sample of liquid water at \(100^\circ\text{C}\) (\(q_{\text{vap}}\)). Which of the following correctly compares \(q_{\text{vap}}\) to \(q_{\text{fus}}\) and provides the correct molecular explanation?

A student conducts an experiment to compare the thermal energy required for phase changes of water, \(\text{H}_2\text{O}\). The student measures the thermal energy required to completely melt a \(18.0 \text{ g}\) sample of ice at \(0^\circ\text{C}\) (\(q_{\text{fus}}\)) and the thermal energy required to completely vaporize a \(18.0 \text{ g}\) sample of liquid water at \(100^\circ\text{C}\) (\(q_{\text{vap}}\)). Which of the following correctly compares \(q_{\text{vap}}\) to \(q_{\text{fus}}\) and provides the correct molecular explanation?

- **A.** \(q_{\text{vap}} < q_{\text{fus}}\), because ice has a lower density than liquid water, requiring more energy to expand the crystal structure during melting.
- **B.** \(q_{\text{vap}} < q_{\text{fus}}\), because melting requires breaking covalent \(\text{O-H}\) bonds within \(\text{H}_2\text{O}\) molecules, whereas boiling only disrupts intermolecular hydrogen bonds.
- **C.** \(q_{\text{vap}} > q_{\text{fus}}\), because vaporization requires completely overcoming all intermolecular hydrogen bonds, whereas fusion requires only partially disrupting the hydrogen bonding network.
- **D.** \(q_{\text{vap}} > q_{\text{fus}}\), because vaporization requires breaking intramolecular covalent \(\text{O-H}\) bonds, whereas fusion requires only overcoming intermolecular hydrogen bonds.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119321/*