Chemistry

No Thaw Flaw in the Third Law

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Science  05 Oct 2001:
Vol. 294, Issue 5540, pp. 17
DOI: 10.1126/science.294.5540.17b

At the melting point of a substance, the liquid has a higher entropy than the solid. If the liquid is supercooled below the melting temperature, this entropy difference decreases because the liquid has a larger heat capacity than the solid. Usually kinetics takes over and the liquid freezes, but what if the liquid could be taken to absolute zero? As pointed out by Kauzmann, extrapolations of heat capacities have suggested that the molar entropies of the supecooled liquid and the crystal could become equal at a temperature above absolute zero (a positive Kauzmann temperature TK). In that case, the supercooled, disordered liquid would have negative entropy at absolute zero, in contradiction of the third law of thermodynamics.

Stillinger et al. have analyzed both data for real substances (such as liquid helium and some polymers) as a function of temperature and pressure and results from simulations. They pronounce the third law to be in good shape and also find no support for arguments proposing an “ideal glass transition” based on positive TK values.—PDS

J. Phys. Chem. B. 10.1021/jp011840i.

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