What role does a catalyst play in chemical reactions?

A catalyst plays a critical role in chemical reactions by accelerating the rate at which the reaction occurs without being consumed in the process. This means that while it contributes to lowering the activation energy required for the reaction, it does not affect the overall outcome or the position of equilibrium of the reaction. Catalysts are particularly significant in industrial applications, where they improve efficiency and reduce energy costs.

The other choices incorrectly describe the role of a catalyst. A catalyst does not act as a reactant or a final product; rather, it facilitates the reaction itself while remaining unchanged. It also does not prevent chemical changes from occurring, but instead promotes and speeds them up, thereby enhancing the efficiency of the reaction. Understanding the function of catalysts is fundamental in both chemistry and engineering, particularly in processes that rely on chemical transformations.