Question

For a gas having extremely low molecular weight, which of the following statement(s) is/are correct?

• A. The value of $\frac{n^{2}a}{v^2}$ can be neglected compared with $P$
• B. The value of $Z$ increases with increase in $P$
• C. The value of $Z$ decreases with increase in $P$
• D. The value of compressibility factor is $1-\frac{Pb}{RT}$

Answer 1

Answer: (A), (B)

The value of $Z$ increases with increase in $P$

For gas having low molecular wt, the value of $a$ is also very less. So the term $\frac{a{n}^2}{v^2}$ is less and can be neglected when compared with $P$.
So, the real gas equation reduces to :
$PV=RT+Pb$
$\Rightarrow \frac{PV}{RT}=1+\frac{Pb}{RT}\Rightarrow Z=1+\frac{Pb}{RT}$
So, $Z$ increases with increase in $P$.