Why Do Gases Need Same Speed for Thermal Equilibrium?

[Himanshu_6174]

When two gases are
mixed, if they are to be in thermal equilibrium, they must have the
same average molecular speed. Why or why not?

 

[Simon Bridge]

It's a direct consequence of the definitions of (what is meant by) "thermal equilibrium".

What is the definition of "thermal equilibrium"?
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thereq.html#c2

In terms of the kinetic theory of gasses, what is "temperature" measuring?
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/temper.html#c1

 

[stevendaryl]

When two gases are
mixed, if they are to be in thermal equilibrium, they must have the
same average molecular speed. Why or why not?

Actually, they have the same average molecular kinetic energy. If the two gases have different molecular weights, then then they won't have the same average speed; the more massive molecules will be moving slower than the lighter molecules.

 

[Himanshu_6174]

Thanks stevendaryl, I was thinking the same. Just wanted to confirm :)