ENTROPY DIFFERENCES BETWEEN IDEAL AND NONIDEAL SYSTEMS

The canonical entropy Sk for an ideal (noninteracting) system is compared with the canonical entropy Sh for a similar nonideal system at the same temperature. Using the Gibbs-Bogoliubov inequality, upper and lower bounds are derived for (Sn SK). For classical fluids and for quantum or classical spin systems, the upper bound is found to be identically zero, yielding Sg=Sk. The classical fluid result agrees with a recent finding of Baierlein and gen-eralizes it to a class of momentum-dependent potentials. The spin system result further ex-tends the scope of Baierlein's inequality. For quantum fluids, a discussion of the bounds is given, but no conclusive results are obtained. © 1969, American Association of Physics Teachers. All rights reserved.