Some Effects in Chemisorption Phenomena that are Connected with Activation Energies

Some Effects in Chemisorption Phenomena that are Connected with Activation Energies 

Porter and Tompkins (379) suggest that the phenomenon is caused by surface heterogeneity and that fast chemisorption takes place, with- 

As we have seen in Sec. IX,9, it is not necessary to introduce active and nonactive parts. In the case of iron films, as investigated by Porter and Tompkins, both phenomena apparently occur on the surface which is freely available. Fast chemisorption may quite normally be followed by slow chemisorption associated with an activation energy when the potential curves follow the picture laid down in Fig. 37. The activation energy is a normal consequence of the decrease in the heat of chemisorption. 

Such a desintering might also be responsible for the slow uptake of hydrogen in the case of nickel and of tungsten films. The activation energy would then be due at least partly to the work that is required to reopen the capillary space closed by the previous sintering. 

The occurrence of these types of sites next to each other on the same surface does not seem very probable. If during the experiments quick chemisorption were accompanied by a slow desintering process, the same phenomena would be observed. On the temperature being raised, desorption would occur, resulting in a slightly smaller degree of occupation corresponding with the temperature and pressure employed. This quick desorption would be followed by a slow uptake.of gas molecules that go 

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