Thermodynamics of Adsorption Based on Gas-Solid Chromatography

Abstract

The net retention volume in gas-solid chromatography is expressed in terms of changes in the thermodynamic functions of adsorption and then is used for the experimental determination of these functions. The differential entropy of adsorption is a linear function of the dilferential enthalpy of adsorption, accounted for by assuming a heterogeneous surface and an exponential distribution of adsorption sites with respect to the energy. A criterion for predicting the above “ thermodynamic compensation effect ” is derived. The net retention volume is also expressed in terms of molecular properties and its dependence on the number of carbon atoms in the molecule is explained. Finally, from the results of adsorption of alkanes and cycloalkanes on aluminium oxide, the frequency of the vibrations of the adsorbate molecules normal to the surface is calculated.