The Ideal Gas Model and Its Assumptions
Specification Reference S1.5.1
Quick Notes
- An ideal gas is a theoretical model used to describe gas behavior.
- Key assumptions:
- Gas particles are in constant, random motion.
- Particles have negligible volume compared to the container.
- No intermolecular forces between particles.
- All collisions are elastic – no energy is lost.
- Temperature reflects the average kinetic energy of the particles.
Full Notes
What Is an Ideal Gas?
An ideal gas is a simplified model used in chemistry to help us understand and calculate gas behavior.
Real gases only approximate ideal behavior under normal conditions (room temperature and pressure), but the model itself is based on a set of assumptions. These assumptions enable us to consider that only temperature, pressure and moles of a gas determine the volume occupied, regardless of the type of gas.
Key Assumptions of the Ideal Gas Model
- Particles are in constant, random motion
They move freely in straight lines until they collide with other particles or the container walls. - The volume of individual gas particles is negligible
The size of the gas particles is so small that their total volume is effectively zero compared to the container. - No intermolecular forces exist
There are no attractions or repulsions between gas particles. They do not interact except during collisions. - All collisions are elastic
When gas particles collide, they do not lose kinetic energy. The total kinetic energy before and after a collision is the same. - Temperature is related to average kinetic energy
The higher the temperature, the faster the particles move. All particles have different kinetic energies, but the average increases with temperature.
Real vs Ideal Gases
Real gases behave nearly ideally under high temperature and low pressure. However, at high pressures or low temperatures, real gases deviate because:
At high pressures gas particles occupy space, meaning their volume is no longer negligible.
At low temperatures intermolecular forces become significant, making gases more likely to condense.
Summary
- The ideal gas model simplifies real gas behavior for easy calculations.
- Assumptions include negligible particle volume, no intermolecular forces, and elastic collisions.
- Real gases deviate at low temperatures and high pressures.
- The model explains why gases expand, compress, and respond predictably to temperature and pressure changes.