ABSTRACT
It is well known that in the literature there are more than 100 isotherm equations derived based
on various physical, mathematical, and experimental considerations. These variances are justified
by the fact that the different types of adsorption, solid=gas (S=G), solid=liquid (S=L), and liquid=gas (L=G), have, apparently, various properties and, therefore, these different phenomena should be discussed and explained with different physical pictures and mathematical treatments.
For example, the gas=solid adsorption on heterogeneous surfaces have been discussed with different surface topographies such are arbitrary, patchwise, and random ones. These models are
very useful and important for the calculation of the energy distribution functions (Gaussian,
multi-Gaussian, quasi-Gaussian, exponential) and so we are able to characterize the solid
adsorbents. Evidently, for these calculations, one must apply different isotherm equations
based on various theoretical and mathematical treatments. However, as far as we know,
nobody had taken into account that all of these different isotherm equations have a common
thermodynamical base which makes possible a common mathematical treatment of physical
adsorption. Thus, the main aim of the following parts of this chapter is to prove these common
features of adsorption isotherms.
