Question

A gas will approach ideal behaviour at:
A.Low temperature and low pressure
B.Low temperature and high pressure
C.High temperature and low pressure
D.High temperature and high pressure

Answer 1

Hint: This question can be solved from the knowledge of ideal gases. In an ideal gas, the particles are point sized, have elastic collisions and are indistinguishable.

Complete step by step answer:
An ideal gas thought to be composed of molecules that exert negligible volumes and hence, the pressure exerted by these molecules on the walls of the container in which they are kept is assumed to be zero.
Secondly, the gas particles are very far apart and move fast.
Thirdly, the particles have no features and exert no force on each other besides collision.
Now, when the pressure exerted on the gases is low, the particles are far apart and the volume of the gas is very large in comparison to the volume of the gas molecules. Similarly, high temperatures keep the fast moving due to high energy of the gas molecules.
On the other hand, when the gas pressure increases, the volume of the gas is decreased and the volume of the gas molecules become considerable in comparison to the volume of the gas. Also at low temperature, the mobility of the gas molecules reduces and hence the gas molecules can exert other attractive forces on each other which will dismiss the ideal gas condition.
Hence a gas can approach ideal behaviour only at low pressure and high temperature.

So, option (C) is correct.

Note:During the ideal gas conditions, i.e. as low pressure and high temperatures, the van Der Waals equation is reduced to the ideal gas equation. Considering the volume of the gas to be very large in comparison to the volume of the gas molecules and at high temperature the interaction between the molecules is restrained.