The chemical constant of hydrogen vapour and the failure of nernst’s heat theorem

The recent successful explanation of the specific heats of hydrogen gas at low temperatures by Dennison leaves little doubt that at all low and ordinary temperatures hydrogen must be regarded as a mixture of two sets of molecules, effectively distinct. One of these sets may be called the antisymmetrical molecules, because for these the rotational quantum number isodd and the rotational wave functionantisymmetrical in the nuclei. The other set may be called the symmetrical molecules because for these the rotational quantum number is even and the wave function symmetrical in the nuclei. When account is taken of the orientations of the nuclei the complete wave function is antisymmetrical in the nuclei in all cases. At the temperatures mentioned the rate of change from one of these forms to the other is very slow though not zero, and any changes that actually occur in any experiment as ordinarily conducted will be so few that they can be neglected altogether. In view of what we have said it is natural to discuss the results of any experi­ment at these temperatures as if the hydrogen gas were a mixture of two absolutely distinct sets of molecules. In this case the laws of classical thermo­dynamics of course apply and control the equilibrium properties of the mixture. From the point of view of the actual hydrogen gas this equilibrium is a false or metastable one. Provided, however, that the false equilibrium is attained rapidly compared with the neglected rate of change the thermodynamic pro­perties of the ideal mixture must be true of the actual gas, and we shall assume this in the following discussion.