Intermediate Topic 252 of 1102 States of Matter & Solutions
Liquefaction of Gases
Gases condense when cooled below critical temperature and compressed.
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In-depth explanation of Liquefaction of Gases
Gases are liquefied by cooling them below their critical temperature and then compressing them to a pressure high enough to bring the molecules together as a liquid. Above the critical temperature no amount of compression can produce a liquid, so cooling is always the first step. Industrial methods include the Linde process, which uses the Joule-Thomson effect, and the Claude process, which adds expansion engines to remove more heat. Liquefied gases such as liquid nitrogen and liquefied natural gas are easier to store and transport, and they serve as cryogenic coolants. Liquid nitrogen boils at 77 K, far colder than any household freezer.
Going deeper: Liquefaction of Gases
Key ideas: Guidelines: cool below Tc, then compress to at least the vapour pressure at that temperature. Boiling points: N2 77 K, O2 90 K, H2 20 K, He 4.2 K. LNG is stored near 111 K at about atmospheric pressure, while LPG, mainly propane and butane, is liquefied at roughly 5 to 8 atm at room temperature.
Common mistakes and connections: Students think pressure alone liquefies any gas at any temperature. Another error is calling cryogenic liquids cold storage without noting boil-off: they constantly vaporize and must be vented safely, with liquid nitrogen expanding about 700 times in volume on vaporizing. Related concepts are critical temperature, Joule-Thomson cooling and phase diagrams.
Visualization of Liquefaction of Gases
Critical temperatures: gases must be cooled below Tc before pressure can liquefy them, so He and H2 need extreme cooling. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Liquefied natural gas occupies about 600 times less volume than the same amount of natural gas in the gas phase.
Frequently asked questions about Liquefaction of Gases
What is Liquefaction of Gases?
Gases condense when cooled below critical temperature and compressed.
Is Liquefaction of Gases a beginner, intermediate or advanced topic?
Liquefaction of Gases is a intermediate topic in States of Matter & Solutions. It builds on the vocabulary of beginner topics in this area.
What should I learn before Liquefaction of Gases?
Study these earlier topics in States of Matter & Solutions first: Compressibility Factor, Critical Temperature, Joule-Thomson Effect.
What comes after Liquefaction of Gases?
The next topics in States of Matter & Solutions are Liquid State and Vapor Pressure.
Can I practise Liquefaction of Gases with quizzes?
Yes. The interactive lesson includes a self-check question on Liquefaction of Gases, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Liquefaction of Gases fits in States of Matter & Solutions
Liquefaction of Gases is topic 33 of 109 in States of Matter & Solutions.