The "cratic correction" and related fallacies

The "cratic correction" for removing the contribution of translational motion from standard free energies and entropies of chemical reactions is examined. Although removal of translational effects is useful in interpreting free energy and entropy changes in molecular terms, this particular correction does not do so. No basis for it is found in thermodynamics or statistical mechanics. The appropriate correction for center-of-mass translational motion is derived from classical statistical mechanics. However, the importance of recognizing the proper molecular meaning of the remaining free energy is stressed. In any case, this latter correction, however legitimate, is shown to be futile, since it has long been recognized from classical statistical mechanics that all terms involving momenta (thermal wavelength terms)-be they classified as translational, rotational, vibrational, or whatever-necessarily cancel out in forming the standard free energy change of any chemical reaction from the constituent standard chemical potentials.