Question

Why do the gases at low temperature and high pressure, show large deviations from ideal behaviour?

Answer 1

At low temperature and high pressure, the intermolecular attractions become appreciable. moreover the volume occupied by the gas molecules cannot be neglected in comparison to the volume of the gas. Hence, the real gas show large deviations from ideal gas behavior.
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Answer 2

Generally, a gas behaves more like anideal gas at higher temperature andlower pressure, as the potential energy due to intermolecular forces becomes less significant compared with the particles' kinetic energy, and the size of the molecules becomes less significant compared to the empty space between them.