1. The problem statement, all variables and given/known data 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? 2. Relevant equations 3. 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.