Question

Consider the van der Waals constants, a and b, for the following gases.
$\begin{array}{ccccc}\text{Gas}& \text{Ar}& \text{Ne}& \text{Kr}& \text{Xe}\\ \text{a (atm}d{m}^{6}mo{l}^{-2})& 1.3& 0.2& 5.1& 4.1\\ b\left({10}^{-2}d{m}^{3}mo{l}^{-1}\right)& 3.2& 1.7& 1.0& 5.0\end{array}$
Which gas is expected to have the highest critical temperature?

• A. Xe
• B. Ne
• C. Kr
• D. Ar

Answer 1

The correct option is C Kr

We know the expression of critical temperature which is given by,
$T_c=\frac{8a}{27Rb}$
$T_c\propto \frac{a}{b}$
Among the given gases, $Kr$ has highest ratio of $\frac{a}{b}=5.1$. Therefore, it is expected to have the highest critical temperature.