Question

The compressibility factor of real gas is usually greater than one $(Z>1)$ at high 'T' and high pressure. This is because?

• A. constant 'a' is negligible while 'b' is not
• B. constant 'b' is negligible while 'a' is not
• C. both 'a' and 'b' are negligible
• D. both 'a' and 'b' are not negligible

Answer 1

The correct option is A constant 'a' is negligible while 'b' is not

The compressibility of a real gas is given by,

$Z=1+\frac{Pb}{RT}-\frac{a}{VRT}$

At high $T$, value of $a/VRT$ decreases.

Also at high $T$, $P$ is high due to which $\frac{Pb}{RT}$ increases.

The increase in the second compensates the decrease in the first due to which net value of $Z>1$ .