catalyst

Collision theory explains how chemical reactions occur and why rates of reaction differ. For a reaction to occur, particles must collide. If the collision causes a chemical change it is referred to as a fruitful collision.

Enzymes are catalysts that can help break larger molecules into smaller molecules while remaining unchanged themselves. Like a key for a lock, each enzyme is specific to one molecule. Most also function best within a narrow temperature and pH range. As the temperature rises enzymes catalyse more molecules but beyond a certain temperature most enzymes become denatured.

A graph showing how a reaction speeds up with the addition of a catalyst.

Substance that alters the speed of, or makes possible, a chemical or biochemical reaction but remains unchanged at the end of the reaction. Enzymes are natural biochemical catalysts. In practice most catalysts are used to speed up reactions.

The catalysts used in the chemical industry are often transition metals or their compounds. According to the collision theory, particles must collide before they can react, and the colliding particles must contain enough energy to cause bonds to break. Catalysts increase the rate of reaction by lowering the amount of energy needed for a successful collision. Therefore, more collisions will be successful.