sion and capillary action. Surfaces can be as thin as a single molecule, called
a film. The behavior of that film is intimately related to the properties of sur-
faces in general.
For well-defined solids like crystals, the surfaces themselves can be well de-
fined using Miller indices. (Solids are not always so well defined, but it is cer-
tainly easier to understand them when they are.) What we understand about
them includes the fact that they can influence chemical reactions but not ac-
tually participate in the overall chemistry: they act as catalysts. The ability of a
surface to act as a catalyst depends on several factors, including how easily a
reactant molecule adsorbs onto the surface, how easily a molecule on the sur-
face dissociates, and how easily the resulting atoms combine to make products.
The right combination of reaction and surface can have a major influence on
the rate of the reaction.
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