ABSTRACT
This chapter discusses a situation where both the internal energy and entropy constants are physically relevant. It looks at the behaviour of specific heats of solids as a function of temperature. In the classical theory this is given by the Dulong-Petit law according to which the molar specific heat of solids is constant, with value 3R. This clearly violates Nernst-Planck theorem. But quantum theory makes a dramatic difference. In thermodynamics and classical statistical mechanics, where entropy constants are arbitrary, this scaling principle is of no consequence. But in quantum theory, where entropy constants are fixed, this scaling principle becomes necessary. As enters all thermodynamic relations only as its differential dS, and never on its own, an addition entropy of a constant, independent of the thermodynamic degrees of freedom of the system, does not affect any of these relations.
