Question

The given graph represents the variation of Z(compressibility factor $=\frac{PV}{nRT}$) 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 = 1, 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

The statement b, "For the gas B, b = 0 and its dependence on P is linear at all pressure" is incorrect.
When $Z<1$, the gas shows negative deviation from ideal behaviour and is more compressible. Hence, $b\ne 0$.