A catalyst is substance that speeds up a chemical reaction, without being used up. Catalysts can therefore be used over and over again. They provide a new route for a reaction to take which has a lower activation energy. The catalyst may react during the reaction allthough will, after the reaction has finished, be the same as before it started. It may however be changed physicaly, for example may have been broken up into more pieces. A biological catalyst is called an enzyme. A reaction that uses a catalyst is the Haber process

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