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Re: [Phys-L] phase change



1. Why is there a definite sublimation temperature T?


The idea only works at constant /pressure/, with the solid
nearly in equilibrium with its vapor.

With that added requirement, the explanation is pretty simple.
All physics is /locall/. Look at what is going on locally at
the surface. The surface doesn't know how much solid is
behind it or how much vapor is in front of it; all it knows
is the local temperature, pressure, density, et cetera.
None of that changes as the reaction progresses.


I interpret this idea to mean: Since the gas and liquid are in thermal contact (at the surface) and in (at least quasi) equilibrium, they have to be at the same temperature.

Fair enough, I can’t object that. I now revise my question 1 to:

1. Do the particles in the gas and in the liquid have the same (a) average kinetic energy? (b) average total energy?

With regards to 1(a), I still wonder if folks think the animation on the following page is basically okay or not:

http://zonalandeducation.com/mstm/physics/mechanics/energy/heatAndTemperature/changesOfPhase/changeOfState.html <http://zonalandeducation.com/mstm/physics/mechanics/energy/heatAndTemperature/changesOfPhase/changeOfState.html>

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Carl E Mungan, Assoc Prof of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9b, 572C Holloway Rd, Annapolis MD 21402-1363
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/