Real gases deviate from ideal gases under which conditions?

• A. High temperature and high pressure
• B. Low temperature and low pressure
• C. Low temperature and high pressure
• D. Gases at very low density

Answer: (C)

Real gases differ from ideal behavior when the assumptions of the ideal gas law break down: particles have finite size and there are intermolecular forces between them. This becomes significant when temperature is low and pressure is high.

At low temperature, the kinetic energy of molecules is reduced, so attractive forces between them become more important. These forces pull molecules closer together and reduce the pressure for a given volume compared with the ideal gas prediction, causing noticeable deviation.

At high pressure, molecules are packed more tightly, so the actual volume occupied by the molecules and the repulsive interactions between them matter. This makes the gas take up less or more volume than the ideal gas law would suggest, again leading to deviation.

Putting these together, the conditions where real gases deviate the most are low temperature and high pressure. At very low density (low pressure) or high temperature, the gas behaves more like an ideal gas.