Four gas cylinders containing He, N2, CO2 and NH3 gases separately are gradually cooled from a temperature of 500 K. Which gas will liquefy first? (Given Tc in K – He : 5.3, N2 : 126, CO2 : 304.1 and NH3 : 405.5)
- NH3
- He
- N2
- CO2
Answer
(1) NH3
Solution
A gas can be liquefied only below its critical temperature Tc.
On cooling from 500 K, the gas whose Tc is reached first, i.e. the gas with the highest Tc, liquefies first.
Tc: NH3 (405.5 K) > CO2 (304.1 K) > N2 (126 K) > He (5.3 K)
NH3 liquefies first.
Answer: (1)