Adsorption at Low Coverage Henrys Law

For physical adsorption there is no change in molecular state on adsorption (i.e., no association or dissociation). It follows that for adsorption on a uniform surface at sufficiently low concentrations such that all molecules are isolated from their nearest neighbors, the equilibrium relationship between fluid phase and adsorbed phase concentrations will be linear. This linear relationship is commonly referred to as Henry s law by analogy with the limiting behavior of solutions of gases in liquids and the constant of proportionality, which is simply the adsorption equilibrium constant and is referred to as the Henry constant. The Henry constant may be expressed in terms of either pressure or concentration  

FIGURE 2.5. vant Hoff piois showing temperature dependence of experimental Henry constants for Ar, Kr, and Xe in Unde 5A zeolite crystals. The dotted line represents data for Ar in Linde 4A. (From ref. 14 reproduced by permission of the National Research Council of Canada from the Canadian Journal of Chemisiry, Volume 53, 1975.) 

The temperature dependence of the Henry constant obeys the vant Hoff equation  

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