In chemistry, what does a catalyst do?

A catalyst functions by increasing the rate of a chemical reaction while remaining unchanged upon completion of that reaction. This means that although it facilitates the reaction process, it is not consumed or altered in the course of the reaction. Catalysts achieve this by providing an alternative reaction pathway with a lower activation energy compared to the reaction without the catalyst. As a result, more molecules have the necessary energy to undergo the reaction, leading to an increased reaction rate.

The incorrect options suggest different roles that do not accurately describe the function of a catalyst. For example, decreasing the rate of a reaction would contradict the fundamental purpose of a catalyst. Changing the elements of a chemical reaction implies a fundamental alteration of the reaction itself, which catalysts do not do; they simply expedite existing reactions. Lastly, slowing down temperature changes during a reaction does not align with the primary role of catalysts, which is to speed up the reaction process rather than manage the thermal changes associated with it.