Question

real gases exhibit deviation from ideal behaviour but why do different gases exhibit different extent of deviation?

Answer 1

The reason for the different extent of deviation is due to the attractive or repulsive forces exhibited by them.

• For gases like He, H₂ the Z value increases with increase in pressure (positive deviation). It is because, the repulsive forces become more significant and the attractive forces become less dominant. Hence these gases are difficult to be condensed.
• For gases like CH₄, CO₂, NH₃ etc.., the Z value decreases initially (negative deviation) but increases at higher pressures. It is because: at low pressures, the attraction forces are more dominant over the repulsion forces, whereas at higher pressures the repulsion forces become significant as the molecules approach closer to each other.