Chemical Forums

Specialty Chemistry Forums => Other Sciences Question Forum => Topic started by: Traumatic Acid on November 02, 2018, 10:07:43 PM

Title: Would a mixture of gasses of different densities separate in zero gravity?
Post by: Traumatic Acid on November 02, 2018, 10:07:43 PM

I'm thinking no, why would they?
Say you had a container of various gases, each with a different density. Left undisturbed on the earth they would separate into layers (assuming they don't react with one another) depending on their densities right?
Now if you put this container deep into space free from (or as free as you can get) gravity from any source, would they still separate into layers depending on their density? I wouldn't be surprised if each gas formed it's own group or groups, but they wouldn't separate depending on their density as there is no gravity acting on the particles for that to make a difference I assume.

Yeah some flat earther is trying to convince me that gravity doesn't exist, it's just a bogus theory the government introduced to us in order to explain people walking "upside down". And apparently gasses don't need gravity to separate into layers.

Cheers.

Title: Re: Would a mixture of gasses of different densities separate in zero gravity?
Post by: Borek on November 03, 2018, 05:02:56 AM

Actually they won't easily separate even at normal gravity, as they diffuse and mix thermally. That requires a highly controlled environment, low temperatures (near gases boiling point) and in very tall columns (like 200 meters).

But you are right that there won't be any separation in the case of no gravity. But then, temperature difference between opposite walls of the container can be enough to result in separation due to thermophoresis.

Title: Re: Would a mixture of gasses of different densities separate in zero gravity?
Post by: Enthalpy on November 11, 2018, 05:18:16 PM

Over a few metres, gases initially well mixed don't separate by gravity. A significant change in the composition needs tens of kilometres: noticeable over the thickness of our atmosphere. Very sensitive measurements can detect a gradient over a smaller height.

The situation differs if different gases are initially separated, like carbon dioxide in a cave or a leak of propane in air. Diffusion takes time to mix them, but the equilibrium means a nearly perfect mix. It's because kT is much bigger than the difference of gravitational energy of the constituent molecules over a reasonable height difference, so the thermal energy sends molecules everywhere and their varied mass makes little difference.

This tells why people who separate ²³⁵U from ²³⁸U need many stages of centrifuges as fast as possible. Gravity is inefficient for that.