Chemistry - Real Gas Question with Solution | TestHub

From the graph it is clear that, the value of ' $Z$ ' decreases with increase of pressure. We can explain as follows on the basis of van der Waals' equation. At high pressure, when ' $p$ ' is large, $V$ will be small and one cannot ignore ' $b$ ' in comparison to $V$. However, the team $a/V^2$ may be considered negligible in comparison to ' $p$ ' in van der Waals' equation. $\left(p+\frac{a}{V^2}\right)(V-b)=nRT$ $p(V-b)=nRT$ $\Rightarrow pV-pb=nRT$ or $\frac{pV}{nRT}=1+\frac{pb}{nRT}$ or $Z=1+\frac{pb}{nRT}$ Thus, $Z$ is greater than 1. As pressure is increased (at constant $T$ ), the factor $\frac{pb}{nRT}$ increases. This explains why after minima in the curves, $Z$ increase continuously with pressure. Hence, the only incorrect statement is (b).