Density gradient vs. entropy of mixing

I was wondering how real gases would behave when they are released into a closed container with fixed volume.


For example, suppose we use chlorine and nitrogen gas. Obviously, chlorine has a higher density than nitrogen gas. Now suppose both are released in similar quantities into a container without air, we have a closed system.


From what I remember for ideal gases, they should mix because the entropy of mixing increases overall entropy. However, since the real gases have different densities and gravity is working on them, the nitrogen gas should be on top of the chlorine gas because of buoyancy.


For reference, mixing of liquids is easy to predict, for example water and ethanol mix because intermolecular interactions dominate and buoyancy does not. But what is up with gases?


Which effect prevails here? Or am I missing something? Thanks in advance.




There would be (non-measurable on small scale) molar fraction gradient (Density gradient is always present due hydrostatic compression).


At this state, the rate of chlorine/nitrogen gravitational settling down/up is balanced by the diffusive mixing driven by molar fraction gradient.


 1