Chapter 11 · Gases
11.2Kinetic Molecular Theory: A Model for Gases
9 min · two checks
Predict
What does the kinetic molecular theory assume about the size of gas particles?
The idea
- State the assumptions of kinetic molecular theory.
- Link temperature to average kinetic energy.
The kinetic molecular theory is a model with a few hard claims. A gas is mostly empty space. Particles move in straight lines until they hit something. Collisions with each other and with the walls are elastic: no energy is lost as stickiness. Particles do not attract or repel each other in the ideal version. The average kinetic energy is proportional to the kelvin temperature and is the same for different gases at the same temperature — lighter gases simply move faster to keep that energy.
The model explains why gases are compressible, why they mix, and why pressure rises when you heat a sealed can: faster particles hit the wall harder and more often. It starts to fail when particles are close and slow, near the conditions where the gas is about to become a liquid. Those gases are called nonideal. The laws that follow assume the ideal picture unless the problem says otherwise.
Keep these
- Particles are tiny, far apart, and do not attract in the ideal model.
- Collisions with walls cause pressure.
- Average kinetic energy depends on kelvin temperature only.