On 9/11/2012 7:24, Larry Jaques wrote:
On Mon, 10 Sep 2012 22:28:52 -0400, "Jim Wilkins"
wrote:

"Larry Jaques" wrote in message
Cite, please?

http://en.wikipedia.org/wiki/Partial_pressure

Thanks. Still having trouble wrapping my head around that.
Is the difference that of the compressibility of the gases, or?

"The partial volume of a particular gas is the volume which the gas
would have if it alone occupied the volume.", do they mean that if
there were 21 molecules of oxygen and 79 molecules of nitrogen
compressed into a 1 CC container, if the nitrogen were removed, the
oxygen would be at its partial volume?

Is "the volume" they refer to 1 CC or 0.21 CC in my example?

Both gasses are in the same volume, 1cc.
The molecules of the gasses are mixed in the space.

As pV/T=constant, what happens is that when you remove the
nitrogen the pressure drops to partial pressure of oxygen.
If you want to keep pressure same, you need to change volume
to the partial volume of oxygen. You must keep temperature constant.

So at first:
1cc, 21% O2, 79% N2, total pressure 10bar
now we take nitrogen away, the pressure becomes partial pressure of O2
1cc, 100% O2, pressure 2.1bar
now we compress oxygen to get original pressure
0.21cc, 100% O2, pressure 10bar
This 0.21cc is the partial volume of oxygen.

You can also calculate it from pV/T=nR..
http://en.wikipedia.org/wiki/Ideal_gas_law

I hope this helps. Partial volume is not very usefull concept, IMHO,
while the partial pressure is a very usefull concept in real life.

Kristian Ukkonen.