Catalyst

A catalyst changes the rate of a chemical reaction without being consumed overall. It provides an alternative reaction pathway, typically with a lower activation energy.

Activation energy: The minimum energy required for a chemical reaction to proceed along a particular pathway. Catalysts increase reaction rate by providing a pathway with a lower activation-energy barrier.
Chemical kinetics: The study of chemical reaction rates and how they depend on conditions. Catalysis is understood through its effects on the rates measured by this field.
Haber process: An industrial process that synthesizes ammonia from nitrogen and hydrogen using an iron-based catalyst. It illustrates how catalysis enables large-scale production of a vital chemical.
Autocatalysis: A reaction in which one of its products accelerates the reaction itself. Unlike an added catalyst, the accelerating species is generated as the reaction proceeds.
Transition state: A fleeting, high-energy arrangement of atoms at the top of a reaction pathway. Catalysts stabilize reaction pathways by changing the energy required to reach this arrangement.
Chemical reaction: A process in which substances are transformed into other substances through rearrangement of atoms. A catalyst changes the rate of this process without changing its overall stoichiometry.
Catalytic converter: An exhaust-treatment device that uses catalysts to convert harmful gases into less harmful products. It applies catalysis to reduce pollutants from combustion engines.
Catalyst poisoning: The loss of catalytic activity when substances bind to or alter active sites. It shows how impurities can disable a catalyst without consuming it in the intended reaction.
Catalytic cycle: A sequence of steps in which a catalyst binds reactants, enables transformations, and is regenerated. It shows how a catalyst can participate in intermediate steps yet be restored overall.
Arrhenius equation: An equation relating a reaction rate constant to temperature and activation energy. It describes why lowering an energy barrier can increase a reaction's rate constant.

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