What role does a catalyst play in a chemical reaction?

A catalyst is a substance that accelerates a chemical reaction without being consumed in the process. Its primary role is to lower the activation energy, which is the energy barrier that must be overcome for reactants to be transformed into products. By providing an alternative reaction pathway with a lower activation energy, catalysts enable more reactant molecules to have sufficient energy to overcome this barrier, thereby increasing the reaction rate.

The choice regarding the change in reactant concentration refers to factors that can indeed influence the rate of a reaction but do not specifically define the role of a catalyst. Similarly, although catalysts can influence the rate at which equilibrium is achieved, they do not change the equilibrium position; they merely help reach that position more quickly. Lastly, the idea that a catalyst is consumed during the reaction is inaccurate, as catalysts remain unchanged after the reaction and can participate in multiple reaction cycles. Therefore, the option that accurately captures the unique function of a catalyst is that it increases the reaction rate by lowering the activation energy.