When $He$ gas is expanded into a vacuum,a heating effect is observed. What is the reason for this?

What is the reason for the deviation of pressure from ideal behavior?

$A$ certain quantity of real gas occupies a volume of $0.15 \ dm^3$ at $100 \ atm$ and $500 \ K$ when its compressibility factor is $1.07$. Its volume at $300 \ atm$ and $300 \ K$ (when its compressibility factor is $1.4$) is $........ \times 10^{-4} \ dm^3$ (Nearest integer).

Which gas shows real behavior?

In the van der Waals equation,which term indicates the presence of attractive forces in a gas?

The correct increasing order of the value of van der Waals's constant $a$ for $CH_4, O_2$ and $H_2$ gases is