Tuesday, 25 August 2020

Why does air remain a mixture?


As we all know, air consists of many gases including oxygen and carbon dioxide. I found that carbon dioxide is heavier than O2. Does the volume difference neglect the mass difference? Is it same for all other gases in air or is there another force that keeps all of these gases together?


If I take a breath of a fresh air, will the exhaled air be heavier because of its higher CO2 content? Will it fall on the floor?



Answer



CO2 will, on average, equilibrate slightly lower than O2 in a gravitational field. But the difference in the force of gravity is very small compared to the random thermal motion of the molecules, thus the effect is effectively negligible in day to day life.



In the context of the atmosphere as a whole this can be a non-negligible effect (e.g. this link), and in astrophysical contexts, this can be very important (e.g. this paper or this one).


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