MCS

Catalysis

A substance which provides a mechanism with a higher activation energy does not increase the rate because the reaction can still occur by the non-catalyzed route. An added substance which does increase the reaction rate is not considered a catalyst but a reaction inhibitor. Catalysts may be classified as either homogeneous or heterogeneous. A homogeneous catalyst is one whose molecules are dispersed in the same phase (usually gaseous or liquid) as the reactant's molecules. A heterogeneous catalyst is one whose molecules are not in the same phase as the reactant's, which are typically gases or liquids that are adsorbed onto the surface of the solid catalyst. Enzymes and other biocatalysts are often considered as a third category.