Question

The relation $PV = RT$ can describe the behaviour of a real gas at:
A) High temperature and high pressure
B) High temperature and low pressure
C) Low temperature and low pressure
D) Low temperature and high pressure

Answer 1

We can easily solve the question if we know the difference between ideal gases and real gases. They tend to behave differently and obey gas laws under specific conditions. Here the equation given in the question is known as the ideal gas equation.

Complete answer:
Let’s first find out the difference between an ideal gas and a real gas.
The kinetic theory of gases put forward two different kinds of gases. Namely, the ideal gas and the real gas.
Ideal gas. A gas which obeys the general gas equation and other gas laws under all conditions of temperature and pressure is known as ideal gas or perfect gas.
The molecules of an ideal gas,
1. Occupy negligible or no volume
2. Have no intermolecular attractive forces.
However, none of the known gases obeys the gas laws or the gas equation ($PV = nRT$, where $P$ is the pressure, $V$ is the volume of the gas, $T$ is the temperature of the gas, $R$ is the universal gas constant and $n$ is the number of gas moles) under all conditions of temperature and pressure.
Hence the concept of ideal gas is only hypothetical.

Characteristics of Ideal gases are:
1. The values of the product of pressure and volume, that is, $PV$ of a gas at constant temperature remains constant. (Boyle’s Law)
2. One mole of ideal gas at $NTP$ occupies $22.4Litres$.
3. The volume of a given mass of gas at constant pressure decreases continuously with decrease in temperature. It becomes zero at $0K$. (Charles's Law)
Let’s now define Real gas. A gas which does not obey the general gas equation and all other gas laws strictly but tends towards ideality at low pressure and high temperature is known as real gas.
Thus from their very definition, we can conclude that an ideal gas is a gas which obeys the equation $PV = RT$ under all conditions of temperature and pressure, but a real gas tends to obey these laws under conditions, such as when the temperature is high and pressure is low.

Thus option B is the correct answer.

Note: The ideal gas equation is the consequence of all other standard gas laws. That is the Boyle’s Law, Charle’s Law, Gay-Lusac’s Law and Avogardo’s Law. We can derive every other gas law from the ideal gas equation. In the expression of the ideal gas equation, the symbol $R$ represents universal gas constant. Its SI unit is $J{K^{ - 1}}mo{l^{ - 1}}$ and its value is $8.314$.