A catalyst is a substance that increases the rate of a chemical reaction by lowering the activation energy without being used up in the reaction.

Catalysts are chemical compounds that increase the rate of a reaction by lowering the activation energy required to reach the transition state. Unlike reactants, a catalyst is not consumed as part of the reaction process. Catalysts do not change the equilibrium constant of the reaction. The process of speeding up a reaction by using a catalyst is known as catalysis.

Catalysts can be divided into two types depending on the reaction phase that they occupy: homogeneous or heterogeneous.

Homogeneous catalysts are those that occupy the same phase as the reaction mixture (typically liquid or gas). Acid catalysis, organometallic catalysis, and enzymatic catalysis are examples of homogeneous catalysis. An advantage of homogeneous catalysis is that the catalyst mixes into the reaction mixture, allowing a very high degree of interaction between catalyst and reactant molecules.

Heterogeneous catalysts occupy a different phase. Generally, heterogeneous catalysts are solid compounds that are added to liquid or gas reaction mixtures. The reason such catalysts can speed up a reaction is that they align molecules in just the right way so that it’s easier for them to combine and react colliding with proper orientation.

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Key Points

• Catalysts are chemical compounds that increase the rate of a reaction by lowering the activation energy required to reach the transition state.

• Catalysts can be divided into two types: homogeneous and heterogeneous.

• Homogeneous catalysts occupy the same phase as the reaction mixture, while heterogeneous catalysts occupy a different phase.

• Homogeneous catalysts allow for greater interaction with the reaction mixture than heterogeneous catalysts.

Key Terms

Activation energy: The minimum quantity of energy which the reacting species must possess in order to undergo a specified reaction.

Transition state: A chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest potential energy along this reaction coordinate.

Reactant: A substance that takes part in and undergoes change during a reaction.

Catalysis: The acceleration of a chemical reaction by a catalyst.

Reaction rate: The speed at which a chemical reaction proceeds.

Catalyst: A substance that increases the rate of a chemical reaction without being consumed in the process.

Homogeneous catalyst: Those that occupy the same phase as the reaction mixture (typically liquid or gas).

Heterogeneous catalyst: Those that occupy a different phase as the reaction mixture.