Define a catalyst.

A catalyst is something that increases the rate of a reaction by lowering the activation energy but is not used in a reaction and does not affect the products.

A catalyst is any compound that is added to a chemical reaction that improves the rate at which the chemical reaction takes place. The catalyst does not undergo a permanent chemical change and is recycled after the reaction has taken place.

A catalyst speeds up a chemical reaction but is itself unchanged at the end of the reaction. It does this by providing an alternative route for the the reaction to occur which has a lower activation energy than the uncatalysed route. With a catalyst, when reactant particles collide, more will have energy greater than the activation energy, so there will be more frequent successful collisions and so a faster rate of reaction.