I'm looking for a something different than the "T is average KE, heat is energy, so adding heat increases the KE and therefore T" explanation. Let's call that the "thermo" side of the argument, which I agree with, but I'm looking at the other side. I'm talking about putting the "dynamics" back in thermodynamics.
That's right - good old fashioned, classical, high school, Newtonian dynamics - the kind grandma used to make: F * d = 1/2 mv^2. My thought is that both F and d increase at higher T, and below is my line of thinking.
Just to keep it as simple as possible, consider a monoatomic gas (say He) at constant V. No vibrations or rotations, just translation. No attractive forces, just electronic repulsion. The number of molecules (atoms) can either be two, or 10^23, as long as they all act the same. I'll assume two molecules, A and B. Here is my line of reasoning:
- Heat is added to the gas in the form of IR radiation.
- Both A and B absorb a photon.
- Both electron clouds increase in size.
- @ constant V, this forces the electrons of the two molecules closer together.
- This increases the (Coulomb) force of repulsion.
- Thus F (at least Fmax) between the two is higher than before the heat addition.
- Now for the distance d through which F acts. F starts at a separation distance closer than before heat addition.
- F falls off as 1/d^2 until reaching "0" at some dfinal. This dfinal is the same as before heat addition.
- Thus, the d through which F acts is also larger than before heat addition.
Therefore, F * d has increased, so has 1/2 mv^2 and therefore T.
Does the above line of reasoning seem valid?