1.5.1—Ideal gas model assumptions
- Syllabus
- First assessment 2025
- Objective
- 1.5.1
- Level
- HL
The Ideal Gas Model
| Assumption | Ideal-gas statement |
|---|---|
| Particle motion | Particles move continuously |
| Particle volume | Particle volume is negligible compared with the gas volume |
| Intermolecular forces | Forces between particles are negligible |
| Collisions | Collisions are elastic |
An ideal gas is a simplified particle model. Use its assumptions as a checklist before deciding whether PV=nRT is a suitable description of a real sample.
Use the assumptions to make predictions: compressing a gas until particle volume is no longer negligible weakens the model, while raising temperature usually reduces the relative importance of attractions. Ideal particles still move and collide; only the collisions are treated as elastic.
Gas pressure arises from particle collisions with the container walls and the associated momentum transfer. At a higher Kelvin temperature, the greater average kinetic energy established in Structure 1.1.3 changes the collision behaviour; this does not replace the separate assumptions that particle volume and intermolecular attractions are negligible.
Ideal Gases Summary
Retrieve the model: ideal particles have negligible volume and forces with elastic collisions; low temperature and high pressure expose real-gas limits; molar volume and PV=nRT then connect amount, pressure, volume, and temperature.
Before calculating, check whether the question uses STP molar volume or PV=nRT, identify the fixed conditions, convert temperature to kelvin, and align pressure and volume units.