Catalysts are substances that increase the rate of a reaction without being consumed by the reaction. These substances function by providing a pathway with a lower activation energy. Catalysts work by reacting to form activated complexes with lower energies or labile (low stability) compounds that react quickly to form the desired products and the catalyst.

A catalyst may be a simple metal ion for the decomposition of hydrogen peroxide, or a complex enzyme with a molar mass of several 100000g/mol for many biological reactions. Catalysts function by becoming involved in the reactions and offering a pathway with lower activation energy.

Some catalysts such as zeolite cages and enzymes also lower the geometric factor by holding a reacting species in the proper orientation for reaction to occur.

While catalysts are defined as substances that do not change the products of a specific reaction, in complex systems where several reactions are possible, one pathway is usually favored by the catalyst. A catalyst can practically eliminate some "side reactions" by accelerating the main reaction.

Catalysts