MediumChemistryHigh School (11–12)States of MatterNumericalBoard Exam AP A-Level IB

For ammonia, a = 4.225 L² bar mol⁻² and b = 0.0371 L mol⁻¹…

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For ammonia, $a = 4.225\ \text{L}^2\ \text{bar mol}^{-2}$ and $b = 0.0371\ \text{L mol}^{-1}$ . Use the van der Waals equation to find the critical temperature, the critical pressure and the critical volume. The measured critical temperature is $405.5\ \text{K}$ . Can ammonia be liquefied by pressure alone at $25\ ^\circ\text{C}$ ?

Need a reminder? The key ideaShow

$Z = PV_m/RT$ . The van der Waals equation is $\left(P + \dfrac{an^2}{V^2}\right)(V - nb) = nRT$ . Its critical constants are $T_c = \dfrac{8a}{27Rb}$ , $P_c = \dfrac{a}{27b^2}$ and $V_c = 3b$ . From $T_c$ and $P_c$ , $b = \dfrac{RT_c}{8P_c}$ and $a = \dfrac{27R^2T_c^2}{64P_c}$ . The Boyle temperature is $T_B = a/(Rb)$ .

The worked solution

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