Catalysis is the change in velocity of chemical reaction in the presence of certain substances, the so-called catalysts. Participating in the reaction, a catalyst in the end it remains chemically unmodified. A small amount of catalyst can help transform the very large number of reacting substances.
Catalysis is called positive when the catalyst increases the reaction rate, and negative when the catalyst reduces the reaction rate. Very common autocatalytic reaction in which chemical process accelerates or slows down the reaction product; these include many combustion processes, some biochemical processes (see biological Oxidation). The phenomenon of catalysis common in nature. The reactions in cells and tissues of organisms involved numerous catalysts, providing sufficient intensity vital biochemical processes (respiratory, digestive and other). These catalysts are called enzymes (see), or enzymes.