Question

It is observed that $H_2$ and $He$ gases always show positive deviation from ideal behaviour i.e., $Z>1$. This is because

• A. the value of $a$ is very large due to high attractive forces
• B. the weak intermolecular forces of attraction due to which $a$ is very small and $a/V^2$ is negligible
• C. the value of $b$ is very large due to large size of the molecules
• D. both $a$ and $b$ are very small and negligible.

Answer 1

Answer: (B)

Position deviation of $H_2$ and He from ideal behavior $(Z=1)$ i.e, $Z>1$ is because of weak inter molecular forces of attraction due to which a is very small
$\left(P+\frac{a{n}^2}{V^2}\right)(V-nb)=RT$ a is very small $\Rightarrow$ we can reject $\frac{a}{V^2}$
$(P)(V-nb)=RT(Z)$