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
$\left(P+\frac{a n^{2}}{V^{2}}\right)(V-n b)=R T$ a is very small $\Rightarrow $ we can reject $\frac{ a }{ V ^{2}}$
$(P)(V - nb)= RT (Z)$