# Liquefaction of Gases - Critical Temperature And Pressure

### dioxide carbon liquefy helium

Two important properties of gases are important in developing methods for their liquefaction: critical temperature and critical pressure. The critical temperature of a gas is the temperature at or above which no amount of pressure, however great, will cause the gas to liquefy. The minimum pressure required to liquefy the gas at the critical temperature is called the critical pressure.

For example, the critical temperature for carbon dioxide is 304K (87.8°F [31°C]). That means that no amount of pressure applied to a sample of carbon dioxide gas at or above 304K (87.8°F [31°C]) will cause the gas to liquefy. At or below that temperature, however, the gas can be liquefied provided sufficient pressure is applied. The corresponding critical pressure for carbon dioxide at 304K (87.8°F [31°C]) is 72.9 atmospheres. In other words, the application of a pressure of 72.9 atmospheres of pressure on a sample of carbon dioxide gas at 304K (87.8°F [31°C]) will cause the gas to liquefy.

Differences in critical temperatures among gases means that some gases are easier to liquify than are others. The critical temperature of carbon dioxide is high enough so that it can be liquified relatively easily at or near room temperature. By comparison, the critical temperature of nitrogen gas is 126K (-232.6°F [-147°C]) and that of helium is 5.3K (-449.9°F [-267.7°C]). Liquefying gases such as nitrogen and helium obviously present much greater difficulties than does the liquefaction of carbon dioxide.

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you are not provided the any of isotherm of co2. .................. it is not good

over 2 years ago

good and basic definition to avoid confusion

almost 4 years ago

Good article but it must include Some Equations Drirvations Graphs etc.

you are not provided the any of isotherm of co2. .................. it is not good

almost 4 years ago

Tnkz but include some graphs too

over 3 years ago

Nice! Less data but said it well !

almost 3 years ago

not bad it might be more good

good but u may add pictuers ....

over 3 years ago

i got the answer to my question. Thank you.You should try to explain the concept of the question more properly.

almost 3 years ago

The current atmosphere on Venus has an average temperature of 740 K and average pressure of 92 atm (varying by elevation). Both of these are higher than 304 K and critical pressure of 72.9 atm you cite above. Cornell (2014) cites the CO2 on Venus as in a super critical state, which means your definition of critical temperature is violated. In short, at 740K there is a pressure at which CO2 is liquified, although it is a super critical liquification, but the pressure is 92 atm.

almost 3 years ago

Hi this was really really great. Thanks a lot.

over 3 years ago

i got the answer to my question. Thank you.You should try to explain the concept of the question more properly.

over 2 years ago

Thanks about the answer but I am confused to some extent... if critical temperature is a temperature 'AT' or above which a gas cant be liquefied no matter what pressure is applied, then why do you show as the possibility of a gas liquefying when a critical temperature is applied?