Activation Energy with Increasing Degree of Occupation

Changes in Activation Energy with Increasing Degree of Occupation 

Even if there is no activation energy when the first atoms are being chemisorbed, there may be one when the degree of occupation becomes higher. A study of potential curves (Fig. 37) reveals that the decrease in the beat of adsorption with increasing 6 is likely to be accompanied by 

It has recently been realized that in many cases a quickly proceeding chemisorption may be followed by a slower uptake of the same gas. When the pressure is raised, more gas is taken up and the additional uptake de- 

A careful study of the adsorption of various gases on carefully cleaned mercury surfaces has led Kemball 362) to the conclusion that such gases as carbontetrachloride, hexachlorethane, and chloroform are chemisorbed 

In all cases where an activation energy is already present at 0 = 0 (N2 on iron, H2 on contaminated metal surfaces see Sec. V,9) it increases with increasing 0 values. The increase of the activation energy is slower than the decrease of the heat of chemisorption. An examination of Fig. 37 shows that this should be so. The maxima in the potential curves are shifted to the left and the minima of the curves are either at the same distance from the surface—as we have assumed in our figure— 

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