Significant Structure Theory of Physical Adsorption

The significant structure theory of liquids has been modified to describe the physical adsorption of gases on homogeneous solids. Equations have been derived for the isotherm, the isosteric heat, and the critical properties. Good agreement with experiment is obtained for the systems Ar and Kr on graphite. The lack of mathematical rigor in the foundations of the significant structure theory is compensated for to a certain extent by its good results and its arithmetical and conceptual simplicity. Its departure from a rigorous foundation, however, makes it difficult to make improvements or to understand anomalies. The third-order dispersion energy correction for molecules adsorbed on a solid as derived by Sinanoğlu and Pitzer was used to determine the two-dimensional lattice energy and the success of the present theory in predicting the heats of adsorption and the critical temperature is a measure of the validity of their work.