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
may be considered negligible in comparison to '
p ' in van der Waals' equation.
(p+)(V−b)=nRT p(V−b)=nRT ⇒pV−pb=nRT or
pRT=1+ or
Z=1+ Thus,
Z is greater than
1. As pressure is increased (at constant
T), the factor
increases. This explains why after minima in the curves,
Z increase continuously with pressure. Hence, the only incorrect statement is (b).