Abstract :
The standard absolute entropies of many materials are unknown, which precludes a full understanding of their thermodynamic stabilities. We show, for both organic liquids and solids, that entropies are reliably linearly correlated with volume per molecule, Vm (nm3 per molecule) (or molar volume, M/ρ (cm3 mol−1)); thus, permitting simple evaluation of standard entropies (J K−1 mol−1) at 298 K. The regression lines generally pass close to the origin, with formulae:
For organic liquids:S°298(l) (J K−1 mol−1)=1133(Vm (nm3 per molecule))+44orS°298(l) (J K−1 mol−1)=1.881Mρ (cm3 mol−1)+44
For organic solids:S°298(s) (J K−1 mol−1)=774(Vm (nm3 per molecule))+57orS°298(s) (J K−1 mol−1)=1.285Mρ (cm3 mol−1)+57
These results complement similar studies (by ourselves and others) demonstrating linear entropy–volume correlations for ionic solids (including minerals, simple ionic solids and ionic hydrates and solvates), but are now—for the first time—demonstrated for organic materials. Part I of this series of papers applies a similar analysis to ionic solids.
