Explain the physical significance of vander Waals parameter.

Explanation

Van der Waals' equation `[P+(an^2)/V^2](V-b)`
=nRT,
In this equation P=Pressure of gas ,V=volume of gas , n= number of moles of gas , T=absolute temperature a, b are constants called van der Waals' constants. Value of 'a' is a measure of magnitude of intermolecular attractive forces within the gas and is independent of temperature and pressure.
At very low temperatures intermolecular forces become significant. Real gases show ideal behaviour when conditions of temperature and pressure and such that the intermolecular forces are negligible. The real gases show ideal behaviour when pressure approaches zero value of b. It is the measure of magnitude of the actual volume occupied by the gas molecules themselves. At high pressures the volume of the gas is very low. Then the volume occupied the gas molecules themselves cannot be neglected.