Question

The compressibility factor is always greater than 1 and increases with increase in pressure for hydrogen and helium. (True or False)

• A. True
• B. False

Answer 1

The correct option is A

True

The intermolecular forces of attraction in hydrogen and helium are negligible as they are small molecules,that is, the Van der Waals constant ”a” is very very small so that $\frac{a}{V^2}$ is negligible.The Van der Waals equation becomes p(V-b)=RT $\Rightarrow$ pV=RT+Pb

Dividing by RT throughout the equation,we get

$\frac{PV}{RT}=1+\frac{Pb}{RT}$

Now, $Z=\frac{PV}{RT}$ which is greater than 1, and increases with increase in the value of P at constant T.