Advanced Placement (AP) Chemistry Practice Exam

What is the primary effect of a catalyst on a reaction mechanism?

1. It increases the equilibrium constant

2. It lowers the energy barrier for the reaction

3. It decreases the rate of product formation

4. It alters the identity of the products formed

The correct answer is: It lowers the energy barrier for the reaction

A catalyst primarily functions by providing an alternative reaction pathway that has a lower activation energy compared to the uncatalyzed pathway. By lowering the energy barrier for the reaction, a catalyst increases the rate at which reactants are converted into products. This means that more reactant molecules can successfully collide with enough energy to overcome this reduced barrier, leading to a faster reaction without changing the equilibrium constant or affecting the amounts of products and reactants at equilibrium. While a catalyst does not alter the identity of the products formed and does not decrease the rate of product formation, it facilitates the reaction to occur more efficiently. Therefore, the primary effect of a catalyst is indeed to lower the energy barrier for the reaction, enhancing the reaction rate without being consumed in the process.