<P> Catalysis (/ kəˈtælɪsɪs /) is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst (/ ˈkætəlɪst /), which is not consumed in the catalyzed reaction and can continue to act repeatedly . Often only tiny amounts of catalyst are required in principle . </P> <P> In general, reactions occur faster with a catalyst because they require less activation energy . In catalyzed mechanisms, the catalyst usually reacts to form a temporary intermediate which then regenerates the original catalyst in a cyclic process . </P> <P> 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 molecules . A heterogeneous catalyst is one whose molecules are not in the same phase as the reactants, 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 . </P>

Enzymes are described as catalyst which means that they