The Correlation of Standard Entropy with Enthalpy Supplied from 0 to 298.15 K

• Autores: Frank L. Lambert, Harvey s. Leff
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 86, Nº 1 (January), 2009, págs. 94-98
• Idioma: inglés
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• Resumen

  • As a substance is heated at constant pressure from near 0 K to 298 K, each incremental enthalpy increase, dH, alters entropy by dH/T, bringing it from approximately zero to its standard molar entropy So. Using heat capacity data for 32 solids and CODATA results for another 45, we found a roughly linear relationship between So and ΔHo. The plot showing the relationship So ≈ (constant)ΔHo, with constant = 0.0066 K–1, for 77 solids can serve as an enlightening visualization of this relationship for students in general chemistry. The near-linearity can be understood qualitatively in terms of lattice vibrations and internal vibrations within polyatomic units, which are reflected by molar heat capacities and Debye temperatures. This study supports the thesis that thermodynamic entropy and stored internal energy in a solid are intimately related and that entropy can be usefully interpreted as a spreading function, as described in the text.