---
title: "A student investigates the non-ideal behavior of gases at low temperature and moderately high pressure. Separate samples containing exactly \\(1.00\\text{ mol}\\) of \\(\\text{CH}_4\\text{(g)}\\) and \\(1.00\\text{ mol}\\) of \\(\\text{CF}_4\\text{(g)}\\) are placed into identical \\(1.00\\text{ L}\\) rigid containers at \\(250\\text{ K}\\). The student calculates the ideal pressure using \\(PV = nRT\\) and records the experimentally measured pressures in the table below.  | Gas | Temperature (\\(\\text{K}\\)) | Volume (\\(\\text{L}\\)) | Calculated \\(P_{\\text{ideal}}\\) (\\(\\text{atm}\\)) | Measured \\(P\\) (\\(\\text{atm}\\)) | | :— | :—: | :—: | :—: | :—: | | \\(\\text{CH}_4\\text{(g)}\\) | \\(250\\) | \\(1.00\\) | \\(20.5\\) | \\(19.2\\) | | \\(\\text{CF}_4\\text{(g)}\\) | \\(250\\) | \\(1.00\\) | \\(20.5\\) | \\(17.9\\) |  Which of the following best explains why the measured pressure of \\(\\text{CF}_4\\text{(g)}\\) is lower than the measured pressure of \\(\\text{CH}_4\\text{(g)}\\) under these conditions?"
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url: "https://nerd-notes.com/ubq/121469/"
date_modified: "2026-08-23T05:04:44+00:00"
---

# A student investigates the non-ideal behavior of gases at low temperature and moderately high pressure. Separate samples containing exactly \(1.00\text{ mol}\) of \(\text{CH}_4\text{(g)}\) and \(1.00\text{ mol}\) of \(\text{CF}_4\text{(g)}\) are placed into identical \(1.00\text{ L}\) rigid containers at \(250\text{ K}\). The student calculates the ideal pressure using \(PV = nRT\) and records the experimentally measured pressures in the table below.

| Gas | Temperature (\(\text{K}\)) | Volume (\(\text{L}\)) | Calculated \(P_{\text{ideal}}\) (\(\text{atm}\)) | Measured \(P\) (\(\text{atm}\)) |
| :— | :—: | :—: | :—: | :—: |
| \(\text{CH}_4\text{(g)}\) | \(250\) | \(1.00\) | \(20.5\) | \(19.2\) |
| \(\text{CF}_4\text{(g)}\) | \(250\) | \(1.00\) | \(20.5\) | \(17.9\) |

Which of the following best explains why the measured pressure of \(\text{CF}_4\text{(g)}\) is lower than the measured pressure of \(\text{CH}_4\text{(g)}\) under these conditions?

A student investigates the non-ideal behavior of gases at low temperature and moderately high pressure. Separate samples containing exactly \(1.00\text{ mol}\) of \(\text{CH}_4\text{(g)}\) and \(1.00\text{ mol}\) of \(\text{CF}_4\text{(g)}\) are placed into identical \(1.00\text{ L}\) rigid containers at \(250\text{ K}\). The student calculates the ideal pressure using \(PV = nRT\) and records the experimentally measured pressures in the table below.

| Gas | Temperature (\(\text{K}\)) | Volume (\(\text{L}\)) | Calculated \(P_{\text{ideal}}\) (\(\text{atm}\)) | Measured \(P\) (\(\text{atm}\)) |
| :--- | :---: | :---: | :---: | :---: |
| \(\text{CH}_4\text{(g)}\) | \(250\) | \(1.00\) | \(20.5\) | \(19.2\) |
| \(\text{CF}_4\text{(g)}\) | \(250\) | \(1.00\) | \(20.5\) | \(17.9\) |

Which of the following best explains why the measured pressure of \(\text{CF}_4\text{(g)}\) is lower than the measured pressure of \(\text{CH}_4\text{(g)}\) under these conditions?

- **A.** The measured pressure of \(\text{CF}_4\text{(g)}\) is lower because \(\text{CF}_4\) molecules have a greater molar mass than \(\text{CH}_4\) molecules, resulting in a lower average molecular speed and less energetic collisions with the container walls.
- **B.** The measured pressure of \(\text{CF}_4\text{(g)}\) is lower because \(\text{CF}_4\) molecules occupy a larger particulate volume than \(\text{CH}_4\) molecules, which reduces the volume of free space available in the container.
- **C.** The measured pressure of \(\text{CF}_4\text{(g)}\) is lower because \(\text{CF}_4\) molecules have a larger, more polarizable electron cloud than \(\text{CH}_4\) molecules, leading to stronger attractive forces that reduce the force of wall collisions.
- **D.** The measured pressure of \(\text{CF}_4\text{(g)}\) is lower because \(\text{CF}_4\) molecules possess polar \(\text{C}-\text{F}\) bonds that generate net dipole-dipole attractions, which pull molecules toward one another and away from the container walls.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121469/*