On Molecule Symmetry, Latent Heat, and Entropy

Abstract This paper suggested correlating entropy with the geometric symmetry of molecular orbitals rather than with the atomic mass distribution within a molecule. Employing the NIST thermodynamic parameters of substances at saturation, linear regressions of exothermic heat over T give \({{\epsilon}}_{exo}=B-\frac{3+2A}{2}RT\). B is the molar heat of liquefication, which equals the latent heat (\(\varDelta{H}_{v}^{\varPhi}\)) at the boiling point. A reflects the molecule's symmetry; the more symmetric the molecular orbits, the smaller A . For example, the symmetry of inert gas atoms gives the operation number n = 1 in the theoretical frame of the geometric symmetry of atomic mass distribution. However, three p orbitals give n = 7; correspondingly, the A values for Ne, Ar, Kr, and Xe are 2.5518, 2.9104, 2.9140, and 2.9178. Similarly, a tetrahedral C sp 3 gives n = 8, CH 4 : A = 2.9519. Hence, assuming that \(\frac{3+2A}{2}R\) is the lost entropy, \(\frac{n-2A}{2}R\) may be regarded as the residual in liquid. According to the above suggestion, CO is more symmetric than CO 2 . Moreover, the similarity in A between ethylene and ethane, propylene and propane, etc., implies that the C-C π bond should be rotatable rather than rigid. Helium-4 superfluid finds an increase in entropy as T decreases from 3.5 to 0.8 K. Clausius-Clapeyron equation was derived from \({{\epsilon}}_{exo}\).