The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
Ehrenfest Relations
thermodynamic formulas describing the relation between macroscopic characteristics of the phases of a thermodynamic system during a second-order phase transition (for example, the transition of helium from the liquid to the superfluid state and the transition of a ferromagnetic to a paramagnetic):
where p, T, and V are the pressure, temperature, and volume of the system and ΔCp, Δαp, and ΔBT are the changes in specific heat, the isobaric thermal expansion coefficient, and the isothermal compressibility coefficient during the phase transition. The relations were derived by P. Ehrenfest in 1933.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.