Activation energy in physical adsorption
The definition given above would more closely describe chemisorption. At large separation from the surface the interaction is zero. In physisorption the interaction becomes attractive and forms a potential well as the surface is approached. There is no activation energy needed to do this. At shorter separations than the potential minimum, the potential becomes repulsive. The minimum is usually at larger separation than the minimum for equivalent species exhibiting chemisorption. Species may physisorp before chemisorption occurs



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