AP Chemistry 3.6.A: Deviation from the Ideal Gas Law
Explore AP Chemistry 3.6.A questions on why real gases deviate from ideal behavior because of interparticle attractions and particle volume.
- Syllabus
- Effective Fall 2025
- Course
- AP Chemistry
Exam points
- Explain how acid-base equilibria depend on dissociation, conjugate pairs and solution conditions.
- Apply equilibrium constants and buffer relationships to calculate pH and predict acid-base changes.
3.6.A—Explain the relationship among non-ideal behaviors of gases, interparticle forces, and/or volumes question 1
[Maximum number: 1]
A student investigates gas behavior using a rigid cylinder with a movable piston of negligible mass, as shown in the diagram above. The cylinder contains 0.325 mol of O2(g).
The student further cools the cylinder to −180∘C and observes that the measured volume of the O2(g) is substantially smaller than the volume that is calculated using the ideal gas law. Assume all equipment is functioning properly. Explain why the measured volume of the O2(g) is smaller than the calculated volume. (The boiling point of O2(l) is −183∘C.)
For a valid explanation: 1 point
The ideal gas law assumes that gas particles do not experience interparticle attractions. As a real gas cools further, the intermolecular forces have greater effect as the average speed of the molecules decreases, resulting in inelastic collisions. To maintain a gas pressure of 1.00 atm, the volume must decrease to accommodate more collisions with less energy.
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