How does a catalyst speed up a chemical reaction?

A catalyst is a substance that speeds up a chemical reaction, but is not consumed by the reaction; because a catalyst can be recovered chemically unchanged at the end of the reaction, it has been used to speed up, or catalyze, the reaction.

For a reaction to occur, the bonds within the reacting molecules rearrange to form the bonds in the product molecules. This isn’t an easy process, however. The reaction requires a certain amount of energy to kickstart the process, and this amount is known as the “activation energy”. A catalyst works to create a new route to form the product that requires a lower activation energy for the reaction, and thus the products can be achieved quicker than trying to surmount the higher activation energy boundary that the uncatalysed reaction.

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Density and pressure