Chemical combinatorics. Part II. On the third law of thermodynamics

Abstract

A given set of atomic particles may often be assembled to form various kinds of ideal crystal, only one of which can, in principle, be stable at 0°K. This variety may arise from structural or other types of molecular isomerism, from the existence of mixed crystals, etc. A graph-theoretical proof that members of a set of such interconvertible crystals do not differ in combinatorial entropy, forms an essential part of the deduction of the third law from statistical mechanics. The accepted version of Nernst's heat theorem must be strengthened by the rider that ΔS(0°K)= 0 for chemical reactions involving metastable ideal crystals, which brings it into line with current practice in the field of standard thermodynamic data.