For H2 gas, the compressibility factor, Z = PV/n RT is:

For hydrogen and helium, the compressibility factor Z is always greater than 1 and increases with increase in pressure. This is because hydrogen and helium being very small, the intermolecular forces of attraction in them are negligible i.e ‘a’ is very small so that 2 a V is negligible. Thus, Van der Waal’s equation, therefore, become Gaseous State 22 1 1 1 PV RT Pb PV Pb RT RT Pb Z RT Z >> >> >>