Question

The given graph represent the variations of $Z$ (compressibility factor $\left(Z\right)=\frac{pV}{nRT})$ versus $P$, for three real gases $A,B$ and $C$. Identify the only incorrect statement.

• A. For the gas $A,a=0$ and its dependence on $P$ is linear at all pressure.
• B. For the gas $B,b=0$ and its dependence on $P$ is linear at all pressure.
• C. For the gas $C$, which is typical real gas for which neither $a$ nor $b=0$. By knowing the minima and the point of intersection, with $Z=11,a$ and $b$ can be calculated.
• D. At high pressure, the slope is positive for all real gases.

Answer 1

Answer: (B)

For the gas $B,b=0$ and its dependence on $P$ is linear at all pressure.

At low pressure, the value of $b$ can be neglected in comparison to a very large value of $V$. At high pressures, $V$ is small and b cannot be neglected.

The variation of $b$ with temperature is given by the equation $PV=RT+Pb$

Hence, statement $\left(B\right)$ is incorrect.