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Water Adsorption by Dry Soil and Its Thermodynamic Functions
Author(s) -
Cary J. W.,
Kohl R. A.,
Taylor S. A.
Publication year - 1964
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1964.03615995002800030007x
Subject(s) - loam , relative humidity , adsorption , thermodynamics , humidity , water vapor , heat capacity , entropy (arrow of time) , chemistry , isothermal process , soil water , soil science , environmental science , physics , organic chemistry
The adsorption of increments of water vapor on Millville loam soil was studied in an air‐free system. The resulting data included the amount of water that would condense on the soil at different relative humidities up to 90% at 14.8°, 24.8°, and 34.8°C. The temperature rise of the samples during adsorption was also recorded and the heat liberated during the reaction was calculated. Both integral and differential thermodynamic values were computed. A critical evaluation of the entropy function showed the integral values to be more useful than the differential values so far as describing the physical state of the system was concerned. In general, calculations of thermodynamic quantities based on the temperature dependence of the systems proved to be unreliable at low relative humidities due to changes in the available surface. Specific conclusions drawn from the data suggest that when equilibrium relative humidity is < 80% in an air‐free Millville loam system, the average entropy of the adsorbed film is a little greater than that of corresponding liquid water, but the average internal energy of the film is always less than that of liquid water, even though the heat content may become slightly greater as the relative humidity rises above 70%.