> > > I'm trying to understand an aspect of the simultaneous diffusion
> > > (effusion?*) =A0of several gases through a permeable membrane between=
 two
> > > spaces.

> Isn't this 'osmosis' ??

Not technically  - osmosis is the special case, but essentially the same th=
ing.

> You might want to look up chromatography

I've already looked up many many many things :-).
The question is not HOW it works from a descriptive point of view or
what happens but how the existence of a particular fraction of a given
gas is "known" about by the same gas on the other side of the
membrane. I can calculate WHAT happens but need to know why.
It would make sense if gases of equal molar fraction or molecular
number were interchangeable in the target gas, but the explanations
claim that it is the moles of the actual gas that count.

eg if I contrive two gases A & B of equal molecular number.
If the partial pressure of A is equal on both sides of the membrane
then no diffusion of A will occur. No problem.
But according to what I read if there is A on one side and B on the
other both with equal partial; pressures then both will diffuse in
opposite directions until the partial pressures of each is balanced.
The rate at which this balancing will occur will almost always be
unequal between the two cases as a given membrane / gas combination
has a species specific rate constant.


                 RM.

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