---
title: "A student separately places identical amounts of gaseous ammonia and methane in rigid containers of equal volume. At each temperature, no condensation is observed. The student calculates the ideal-gas pressure using \\(P_{\\text{ideal}}V=nRT\\) and records the following data.  | Gas | \\(\\dfrac{P_{\\text{measured}}}{P_{\\text{ideal}}}\\) at \\(500\\text{ K}\\) | \\(\\dfrac{P_{\\text{measured}}}{P_{\\text{ideal}}}\\) at \\(300\\text{ K}\\) | |—|—:|—:| | \\(\\text{NH}_3\\text{(g)}\\) | \\(0.98\\) | \\(0.95\\) | | \\(\\text{CH}_4\\text{(g)}\\) | \\(1.02\\) | \\(1.01\\) |  Which of the following statements best explains why the pressure ratio for \\(\\text{NH}_3\\text{(g)}\\) is lower than that for \\(\\text{CH}_4\\text{(g)}\\) and decreases more upon cooling?"
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url: "https://nerd-notes.com/ubq/120060/"
date_modified: "2026-08-21T08:41:05+00:00"
---

# A student separately places identical amounts of gaseous ammonia and methane in rigid containers of equal volume. At each temperature, no condensation is observed. The student calculates the ideal-gas pressure using \(P_{\text{ideal}}V=nRT\) and records the following data.

| Gas | \(\dfrac{P_{\text{measured}}}{P_{\text{ideal}}}\) at \(500\text{ K}\) | \(\dfrac{P_{\text{measured}}}{P_{\text{ideal}}}\) at \(300\text{ K}\) |
|—|—:|—:|
| \(\text{NH}_3\text{(g)}\) | \(0.98\) | \(0.95\) |
| \(\text{CH}_4\text{(g)}\) | \(1.02\) | \(1.01\) |

Which of the following statements best explains why the pressure ratio for \(\text{NH}_3\text{(g)}\) is lower than that for \(\text{CH}_4\text{(g)}\) and decreases more upon cooling?

A student separately places identical amounts of gaseous ammonia and methane in rigid containers of equal volume. At each temperature, no condensation is observed. The student calculates the ideal-gas pressure using \(P_{\text{ideal}}V=nRT\) and records the following data.

| Gas | \(\dfrac{P_{\text{measured}}}{P_{\text{ideal}}}\) at \(500\text{ K}\) | \(\dfrac{P_{\text{measured}}}{P_{\text{ideal}}}\) at \(300\text{ K}\) |
|---|---:|---:|
| \(\text{NH}_3\text{(g)}\) | \(0.98\) | \(0.95\) |
| \(\text{CH}_4\text{(g)}\) | \(1.02\) | \(1.01\) |

Which of the following statements best explains why the pressure ratio for \(\text{NH}_3\text{(g)}\) is lower than that for \(\text{CH}_4\text{(g)}\) and decreases more upon cooling?

- **A.** The increasingly negative deviation of \(\text{NH}_3\text{(g)}\) results from cooling, which lowers molecular kinetic energy and makes its permanent dipole–dipole attractions, including hydrogen bonding, more significant. The weaker attractions in nonpolar \(\text{CH}_4\text{(g)}\) do not overcome the excluded-volume effect.
- **B.** The increasingly negative deviation of \(\text{NH}_3\text{(g)}\) results from cooling, which substantially increases the permanent dipole moment of each \(\text{NH}_3\) molecule and thereby creates stronger dipole–dipole attractions.
- **C.** The increasingly negative deviation of \(\text{NH}_3\text{(g)}\) results because its greater molar mass gives its molecules less average translational kinetic energy than \(\text{CH}_4\) molecules at the same temperature, allowing attractions to dominate.
- **D.** The increasingly negative deviation of \(\text{NH}_3\text{(g)}\) results mainly from the finite volume of its molecules, because molecular volume reduces the volume available for motion and therefore decreases the measured pressure below the ideal pressure.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120060/*