Advanced Placement (AP) Chemistry Practice Exam

A catalyst plays a crucial role in chemical reactions by providing an alternative pathway with a lower activation energy for the reactants to convert into products. This allows the reaction to proceed more rapidly without changing the overall energy of the system or the position of equilibrium.

When a catalyst is present, it facilitates the formation of the transition state, which is a temporary state that reactants must pass through before forming products. By lowering the activation energy, a catalyst effectively increases the number of reactant molecules that possess enough energy to overcome this barrier within a given timeframe, leading to an increase in the reaction rate.

Importantly, a catalyst is not consumed in the reaction, meaning it can participate repeatedly in multiple reaction cycles without being permanently altered or used up. This ability to be reused is a significant aspect of catalysts in various industrial and biological processes.

In contrast, the other options do not accurately describe the role of a catalyst. A catalyst does not change the equilibrium constant as it does not affect the thermodynamics of the reaction; rather, it only impacts the kinetics. Additionally, it does not increase the activation energy; instead, it decreases it. Lastly, a catalyst does not change the products formed in the reaction; it merely helps the reaction reach those products more quickly