Question

The vander waals constant for gases $A,B$ and $C$ are as follows:

$\begin{array}{ccc}\text{Gas}& {\text{a/dm}}^6{\text{kPa mol}}^{-2}& {\text{b/dm}}^3{\text{mol}}^{-1}\\ A& 405.3& 0.027\\ B& 1215.9& 0.030\\ C& 607.95& 0.032\end{array}$

Which gas has highest critical temperature :

• A. $A$
• B. $B$
• C. $C$
• D. All have same critical temperature.

Answer 1

The correct option is B $B$

We know, $T_c=\frac{8a}{27Rb}$, Since, $R$ is constant, so higher the value of ratio $\frac{a}{b}$, higher will be the critical temperature. Also the value of $‘b^{\prime }$ is nearly the same for all the gases. Hence higher the value of $‘a^{\prime }$ higher is the value of $T_c$ , gas $B$ has the highest value of $‘a^{\prime }$ and hence highest critical temperature.