Which set of conditions represents the easiest way to liquify a gas?
(1) Low temperature and high pressure
(2) High temperature and low pressure
(3) Low temperature and low pressure
(4) High temperature and high pressure
Answer: (1) Low temperature and high-pressure set of conditions represent the easiest way to liquefy a gas. Liquefaction of gases is a physical conversion of a gas into a liquid state (condensation). The processes are used for scientific, industrial and commercial purposes. Many gases can be put into a liquid state at normal atmospheric pressure by simple cooling; a few, such as carbon dioxide, require pressurization as well. Liquefaction is used for analyzing the fundamental properties of gas molecules (intermolecular forces), for the storage of gases. The liquefaction of gases is a complicated process that uses various compressions and expansions to achieve high pressures and very low temperatures, using, for example, turbo-expanders.
