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Tue 10 May, 2005 02:02 pm

I was just wondering what were some of the differences between real and ideal gases.. I know that ideal gases obey all the gas laws.. and I'm assuming that a real gas doesn't? Help.. someone.. please

Much thanks,

Rose

All real gases fail to conform to at least on of the set of laws attributed to all gases. So basically they only need to fulfill 90% of the requirements.

An ideal gas follows the equation PV=nRT. (in actuality no gasses follow this exactly, but a great many very come close, especially depending on your system's temperature and pressure). A real gas significantly deviates from PV=nRT (the Ideal Gas Law).

To account for this, we throw in a fudge factor "Z" to account for non-ideality. So the equation is now PV=ZnRT. Z is a function of the reduced temperature and reduced pressure of the gas (or gas mixture) at your pressure and temperatue. There are numerous other "equations of state" that you can use to account for non-ideality, but PV=ZnRT is the easiest to do by hand (if you are using any of the canned Process programs you are given a choice between 20 or 30 of them).

An ideal gas is a monatomic gas with no potential electronic interaction with its neighbors. An ideal gas molecule has mass and velocity (temperature) but no volume. It does not condense, nor does it have a triple point. Helium comes is the closest to being an ideal gas.

Real gasses condense; have electronic interactions, mass, velocity (temperature), and volume. It both condenses and sublimates and has a triple point. Many real gasses behave like ideal gasses over a wide pressure and temperature range.

Ideal gasses obey PV=nRT where Pressure, Volume, Temperature, and molal inventory are variables and R is a gas constant.

This allows comparisons to other ideal gasses by P1V1/(n1T1)=P2V2/(n2T2)

Many other real gas laws exist to compensate for the non-ideal behavior of real gasses (note these will contain many additional variables)*

Rap

With 10 points I can describe an elephant; with 11 he'll wag his tail--Euler