Uncertain about my understanding of the Joule-Thomson effect

Before i get to the questions I have; I am a high school student. We are not asked to understand thermodynamics nor real gases. I'm simply trying to understand the topic without diving too much into the calculations/derivations.

• 1): Why does sudden expansion of (most) gases cause a cooling effect?

• 1.1): Looking at the horrible paint drawing of two chambers and a tube connecting them (V1=V2),(P1 > P2). Why is (T2 < T1) after the expansion?
• 2): Why do helium and hydrogen cause a positive temperature difference while all other gases cause a negative one?

My best attempt to explain these problems was the following: Looking at the Lennard-Jones potential graph, If atoms are super close; there is a repulsion (positive potential energy) and when they are at medium range they attract each other (negative potential energy).

Gases flow through c1 to c2 because of the pressure difference (or because of a piston) and as they go through the tube this pressure difference is converted to negative potential energy for gas molecules. Therefore when leaving the tube, they use their own kinetic energy to get out of this bond (it is not a bond, but I don't think I have any other way of phrasing it); which cools the right chamber. Making T2 < T1

For hydrogen and helium, as they have only one shell, they can get nearer to each other which creates a positive potential energy. This potential energy then turns into kinetic energy when entering the second chamber. Making T2 > T1

I feel like I'm quite off from what's actually going on, so any help is appreciated.

• Just want to congratulate you for seeking to understand physics conceptually, it is really important to do this, and not get blind by big calculations. Commented Jul 11, 2022 at 17:56
• Welcome to Physics SE! You are doing very, very well for high-school-level studies. I'm sure you'll be interested that this exact point is the topic of McClure's "The Joule-Thomson coefficient—a molecular interpretation," American Journal of Physics (1971), which considers only a square potential. Note that your dichotomy between H & He and the other gases applies only around room temperature; every gas has its own inversion temperature. Commented Jul 11, 2022 at 20:28
• There is also viscous flow of gas passing through the small diameter tube, and associated dissipation of mechanical energy to internal energy. Hello, can you explain what you mean by this section? I can't seem to follow. Commented Jul 12, 2022 at 8:38