Origin of Zero-Point Entropy

Abstract

EUCKEN and his collaborators have pointed out that the failure of Nernst's heat theorem—the so-called third law of thermodynamics—which occurs in some cases, is due to the zero-point entropy1. A definite zero-point entropy arises from the existence of ‘frozen-in’ phases stable at higher temperatures which do not reach the real thermal equilibrium on cooling to the neighbourhood of the absolute zero. Teske and I, for example, have found that solid carbon monoxide near 10°K. exhibits such a state in spite of its crystalline structure2. Clay ton and Giauque have confirmed this result3 and explained the discrepancy by the suggestion that the asymmetry of the carbon monoxide molecule gives rise to two positions in the lattice of nearly equal energy. The formation of a fully ordered crystal is thus prevented. No such effect is to be expected in the case of nitrogen, which is a symmetrical molecule. Dr. Teller has directed my attention to the fact that similar behaviour may be shown by nitrous oxide as opposed to the symmetrical carbon dioxide: this has proved to be true.