Non-Ideal Gases and Limits of the Ideal Model

The ideal model is an approximation. Real molecules occupy finite volume. They can also attract or repel each other. At sufficiently low density, these effects may be small. But deviations become important particularly when molecules are crowded or intermolecular interactions become significant. **1. Negligible molecular volume Real particles occupy space. 2. Negligible intermolecular forces** Real molecules interact.

A simplified model gives a baseline. Scientists can then understand real systems by examining how and why they depart from the baseline. This is one of the ways the ideal-gas model helped develop statistical mechanics. The current curriculum explicitly uses ideal gases as the starting point for understanding non-ideal behaviour. ([Scribd][2])

Ideal baseline: **pV=NkT Real behaviour: pV ≠ NkT exactly under all conditions**