The critical constants and for four gases are <br><br>Gas | Critical temperature | Critical pressure — States of Matter and Gaseous State Chemistry Question
Question
The critical constants $P_c$ and $T_c$ for four gases are <br><br>Gas | Critical temperature | Critical pressure<br>O₂ | 153 K | 50 bar<br>Cl₂ | 417 K | 76 bar<br>H₂ | 33.9 K | 13.5 bar<br>He | 5.12 K | 2.2 bar<br><br>The gas with smallest value of van der Waal's constant $b$ is
Answer: D
💡 Solution & Explanation
The critical volume $V_c = 3b = \frac{3}{8} \frac{RT_c}{P_c}$, so $b \propto T_c/P_c$. Evaluating $T_c/P_c$: $\text{O}_2 = 3.06$; $\text{Cl}_2 = 5.48$; $\text{H}_2 = 2.51$; $\text{He} = 2.32$. Helium ($\text{He}$) has the smallest ratio and consequently the smallest molecular volume $b$. Therefore, correct answer is D.
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