# Real gases

1. Apr 20, 2005

### siewwen168

hello :tongue2:

i wanna ask about the deviation of real gases under low temperature and high pressure. :tongue:

my reference book states that carbon dioxide deviates more than nitrogen and hydrogen,this is because the order of boiling points of is decreasing from carbon dioxide to hydrogen.this is because carbon dioxide liquefies at a much higher temperature than nitrogen and hydrogen.

can anyone tell me what is the relationship between the ease of liquefaction and the deviation?

anyway ,what is the meaning of liquefaction?is it something to do with it's boiling point??

2. Apr 20, 2005

### pack_rat2

"Liquifaction" (I think that's the correct spelling) just means turning something into a liquid. The Ideal Gas Law assumes that the space occupied by, and the forces between, the atoms/molecules of a gas can be ignored. It's a valid approach for low pressure and high temperature. But how does one define what is "low" and "high" for a particular gas? It has to do with how close the temp/pressure are to the "critical" values. The critical temperature (Tc) of a gas is that at which the gas cannot be liquified. For CO2 that's around 85 deg.F. The critical pressure (Pc) is the pressure at Tc. For CO2 it's around 850 lb/in^2. When one gets near Tc or Pc, the Ideal Gas Law is no longer accurate, and another equation of state, such as the Redlich- Kwong must be used. Hope this helped...

3. Apr 21, 2005

### siewwen168

hi pack rat2,thanks for your help,i think your information is very useful to me.thanks alot.