State properties of adsorbatesJ. Heyrovský Institute of Physical Chemistry and Electrochemistry, Czechoslovak Academy of Sciences, 121 38 Prague
Abstract: The changes of thermodynamic functions of adsorbate caused by changes Δ of its structure in the field of adsorption forces were determined. The analysis of these changes of thermodynamic functions (further denoted as perturbation functions ΔG*, ΔH*, and ΔS*) confirms the validity of two fundamental postulates of the Polanyi —Dubinin theory. It is shown that 1. the Polanyi postulate is valid if the perturbation entropy ΔS* is zero; 2. the condition of the validity of Dubinin postulate is the proportionality of perturbation enthalpy ΔH* of adsorbate with the perturbation enthalpy of the standard adsorbate ΔH0. From the experimental studies of adsorption equilibria the conclusion can be made that in most cases the perturbation entropies and enthalpies are close to zero. The good agreement of the Polanyi —Dubinin theory with the experimental data ensues from a close resemblence of the state properties of most adsorbates (p, v, T relations) to the state properties of vapours and liquids. The exceptions are observed in case of substances associating by means of hydrogen bonds (water, alcohols). The explanation of these deviations made the formulation of a general theory of adsorption for nonspecific interactions feasible. With this general theory it is possible to predict without exception the adsorption equilibria of any gases and vapours on active carbons at any temperature on the basis of three parameters which characterize the structure of micropores (W0, n, and E0). The good agreement of the theory with experimental data is evident from the tables of adsorption isotherms of benzene, argon, ammonia, methanol, ethanol, and water. Full paper in Portable Document Format: 295a660.pdf
Chemical Papers 29 (5) 660–684 (1975) |
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