What is a catalyst?

A catalyst is a substance that significantly increases the rate of a chemical reaction without undergoing any permanent change itself. This means that at the end of the reaction, a catalyst can still be present in its original form. By providing an alternative reaction pathway, catalysts lower the activation energy barrier, making it easier for reactants to convert into products. This characteristic is what allows catalysts to be repeated in numerous reactions without being depleted, emphasizing their role in enhancing reaction rates efficiently.

The option describing the catalyst's ability to speed up a reaction aligns perfectly with this definition. While the mention of decreasing activation energy is also closely related to the function of some catalysts, it doesn't encapsulate the primary aspect of a catalyst being unchanged post-reaction. Understanding that a catalyst is used repeatedly and does not alter its chemical composition is crucial to grasping its role in chemical processes.