Concentration conversion 3

[kmac23]

When can you assume that volume percent is the same as mole percent?
I've read in another posting that you can assume this at low pressure but I'd like to know why and under what conditions.

 

[dcasto]

volume percent and mole percent for gases only. Pressure or temperature do not affect the results. Weight percent on gases will change from mole percent, but pressure and temperature do not affect the results.

 

[CHEMANG]

For gases at low pressures ( atm. pressure - few bars),
mole percent is equal to volume percent. Because we know that at low pressures all gases behave like ideal gases.

-ANG

 

[dcasto]

Unfortuneately, at higher pressures the individual molecules don't understand compressibility so they all mix and, Mole Percent and volume percent are the same, even at pressures above the criticle point.

 

[25362]

If you wish a more detailed approach raise the link titled:

Conversion between mole fractions and volume fractions in gas analysis

 

[CHEMANG]

I guess by critical point dcasto means the point at which all the 3 phases co-exist.

I would be more interested to know about this unfortunate thing about the gases.Can anyone throw more light on it please...

 

[dcasto]

Critcle point, the point on the phase diagram which is the criticle pressure and criticle temperature meet. Once you are above the criticle point, no matter how cold or how much more pressure you put on the system, it CANNOT become a liquid. The fluid is described as a supercriticle fluid. It has the molecular energy of gases, but physical properties closer to liquids.

 

[25362]

For supercritical fluids one may just as well visit:

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