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Re: [Phys-l] Thermodynamics, P vs. T plot



At 7:42 PM -0500 11/23/10, Peter Schoch wrote:
We are beginning Thermodynamics, and I showed them some P vs. T plots, showing the 3 phases (solid, liquid, gas), the triple point, etc. -- mentioning that water was unique for having a transition line between solid and liquid with a negative slope.

Unusual, but not unique.
3He also has a negative slope along it's solid/liquid transition line.

Water's negative slope arises from anomalous delta v
(solid has greater volume than liquid)
3He's negative slope arises from anomalous delta S
(solid has more entropy than liquid)



The question arose asking if anything has a transition line that is vertical or nearly vertical. I admitted to never having seen one, and did not think it was possible -- but I am unsure of that last point.

What would a vertical, or nearly vertical, transition line have as a physical significance? Any insights would be most welcome!

Clausius and Clapyron would require some seriously strange delta (s) / delta (v) => infinity?