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Adsorption-Desorption Equilibria of Herbicides in Soil: Naphthalene as a Model Compound for Entropy-Enthalpy Effects

Published online by Cambridge University Press:  12 June 2017

R. Don Wauchope
Affiliation:
Agr. Res. Service, U.S. Dep. Agric., Stoneville, MS 38776
Ken E. Savage
Affiliation:
Agr. Res. Service, U.S. Dep. Agric., Stoneville, MS 38776
William C. Koskinen
Affiliation:
Agr. Res. Service, U.S. Dep. Agric., Stoneville, MS 38776

Abstract

The adsorption of naphthalene by a Bosket loam soil was studied at 6.5, 15, 25, and 37C. Because the solubility and vapor pressure of naphthalene are precisely known over this temperature range, a complete thermodynamic description of the differences between standard vapor, crystal, solution, and soil-adsorbed states is possible. The results indicate that enthalpies and entropies of the solution and surface standard states are quite similar (though very different from the vapor state) resulting in a near-zero standard enthalpy difference and a small standard entropy increase for adsorption from solution. Considering naphthalene as a model for herbicides and as a probe into the nature of the soil surface, the results emphasize the importance of the unique structured nature of water acting as a solvent, and the competition of water for adsorption sites.

Type
Research Article
Copyright
Copyright © 1983 Weed Science Society of America 

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