Real Gases vs Ideal Gases

The ideal gas model — with its assumptions of point-like particles, no intermolecular forces, and perfectly elastic collisions — is remarkably successful at predicting gas behaviour under everyday conditions. But no real gas is truly ideal. Under certain conditions, real gases deviate significantly from the predictions of pV = nRT. Understanding when and why this happens is important for both exams and practical applications.

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When Do Ideal Gas Assumptions Break Down?

The two most significant assumptions of the ideal gas model are:

1. The volume of the molecules is negligible compared to the volume of the container.
2. There are no intermolecular forces between molecules.

These assumptions are reasonable when the molecules are far apart (low pressure) and moving fast (high temperature). They break down in two key situations:

High Pressure

At high pressures, the gas is compressed into a smaller volume. The molecules are pushed closer together, and: