Question

Gases	$A$	$B$	$C$	$D$
$P_c\left(atm\right)$	$2.2$	$14$	$35$	$45$
$T_c\left(K\right)$	$5.1$	$33$	$127$	$140$

Which of the above gases cannot be liquefied at $100K$ and $50atm$?

• A. $D$ only
• B. $A$ only
• C. $A$ and $B$
• D. $C$ and $D$

Answer 1

Answer: (A)

$D$ only

The gases A and B cannot be liquefied at 100 K and 50 atm as the temperature (100 K) is higher than their critical temperatures (5.1 K and 33 K respectively).
The gases and D can be liquefied at 100 K and 50 atm as the temperature (100 K) is lower than their critical temperatures (127 K and 140 K respectively).
Note:
The critical temperature of a gas is the temperature below which it can be liquefied by application of pressure.
$V_c=3b,P_c=\frac{a}{27b^2},T_c=\frac{8a}{27Rb}$