Why Pure Nitrogen System Evacuates Faster in 500 Microns Vacuum

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Homework Statement



Two closed systems of the same size, temperature, and pressure. One is filled with pure nitrogen the other an atmospheric mix (nitrogen/oxygen/etc...throw in some moisture).

I want to evacuate both systems to 500 microns using equally sized vacuum pumps. Why will the pure nitrogen system evacuate quicker?


Homework Equations





The Attempt at a Solution



My HVAC courses lightly touched on gas behavior. This scenario peaked my interest so I am seeking any explanation or direction to educational resources.

My uneducated guess is that it has to do with the densities equating to more or less work required of the vacuum pump thus change in time.
 
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Water could be interesting: evacuation will cool the air, so water could condensate at the walls (depends on the temperature/pressure curve and the initial humidity). After a while, it will freeze (and slowly sublimate), with a possible boiling step in between.
Nitrogen and oxygen are quite similar, and argon should not be an issue. CO2... depends on the temperature.