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Ideal gas assumptions
Beginner
Point particles with elastic collisions and no forces.
gasThe model treats molecules as point particles with negligible volume, no intermolecular forces except instantaneous elastic collisions, moving randomly. It works well at low density and high temperature.
Air at normal conditions follows it within 1%.
Fails near condensation.
In more detail
The kinetic theory of ideal gases assumes molecules are point particles with negligible volume, no intermolecular forces except during collisions, and elastic collisions with walls. Real gases deviate when these assumptions fail.
Real-world uses
- Engineers model gases in engines and pipelines using ideal assumptions.
- Predicting gas behaviour at low pressure.
- The ideal gas model is a good starting point for air at room temperature, where molecules are far apart and rarely interact.
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Frequently asked questions
When do ideal assumptions fail?
At high pressure, where molecules are close, and at low temperature, where forces matter.
Do molecules collide with each other?
Yes, and these collisions help distribute energy among them.
When does the ideal gas model fail?
At high pressure or low temperature, when molecules are close together and their attractions and volumes matter.
Related topics in Kinetic Theory & Statistical Physics
Molecular picture of matter · Brownian motion · Pressure from molecular collisions · Kinetic interpretation of temperature · Boltzmann constant