Spin-Exchange Term in the Solvent Equation of State Near the Critical Point for Electron-Transfer Reactions

✍ Scribed by J.V. Acrivos

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 408 KB
• Volume: 151
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8629

✦ Synopsis

Phenomenological equations of state (EOS) for 6uids near their critical point have been obtained using literature compression factor data, Z c ‫؍‬ P c V c /(nRT c ) ‫؍‬ 0.40 to 0.10 in (P c , V c , and T c are the pressure, volume per nmole, and the absolute temperature of the 6uid at the critical point). The objective is to explain the deviations from the van der Waals value, Z c (vdW ) ‫؍‬ 3/8 (؊70% for molten Se and alkali metals up to 6% for molten Pb, Hg, and In) by including in the commonly used phenomenological thermodynamic relations a term which explicitly describes the Heisenberg spin-exchange interactions, in order to understand electron-transfer reactions in solvents near their critical point. Literature data near the critical point indicate that the 199,201 Hg(Z c :0.4) Knight shift pluments to zero while the alkali metals and Se (Z c ‫؍‬ 0.2 to 0.1) are paramagnetic 6uids, and that the enhanced rates for free radical electron-exchange reactions in CO 2 , n-C 2 H 6 , and CHF 3 with intermediate values of Z c , are correlated to Z c . The di4erence in the solvent behavior for electron-exchange reactions near its critical point is ascribed to spin-exchange interactions. The analysis shows that the solvated electron osmotic pressure in metal+ammonia solutions goes through a maximum where enhanced rates of electron exchange also attain a maximum versus the solvent density r ‫؍‬ V c /V :0.5. The results can be applied to choose the best solvents, near their critical point, for the syntheses of new materials and heavy metal oxide extraction.