Understanding Molecular Collisions in Gases

[Aero51]

Hey, I'm not sure if this should be in the chemistry or physics section,. Hopefully it is in the right place. I have a question about molecular collisions: specifically, what actually happens when two molecules "collide". Perhaps a better question is: "what constitutes a molecular collision?". Since I have some background in physical gas dynamics and modern physics, I know that it is not possible for the two molecules to actually "touch" each other in the sense of two billiard balls colliding. On this subject, since molecules do not collide in the macroscopic sense, why do they behave as if they are, as stated earlier, billiard balls in a container? If anyone has good references or books please share those too!

 

[mfb]

It is sufficient to have any sort of non-destructive interaction to make "billard balls in a container" a good model. If molecules come close to each other, their dipole moments can influence each other via the electromagnetic interaction. If they come even closer, their electron orbitals begin to overlap, which (usually) generates a repulsive force.

 

[Aero51]

It is sufficient to have any sort of non-destructive interaction to make "billard balls in a container" a good model.

If this is true then what about gases with viscosity? Wouldn't that require one to know (or assume) something about the geometry of the molecules?