Advanced Placement (AP) Biology Practice Exam

What term describes the energy required to initiate a chemical reaction?

1. Activation Energy

2. Potential Energy

3. Free Energy

4. Catalytic Energy

The correct answer is: Activation Energy

Activation energy is the term that describes the energy required to initiate a chemical reaction. This energy is needed to overcome the barriers that prevent reactants from transitioning into products. In a chemical reaction, reactants must attain a certain energy level before they can interact in such a way that bonds can break and form new ones, leading to the products of the reaction. The activation energy is crucial because it determines the rate of the reaction; higher activation energy typically means a slower reaction rate, unless a catalyst is present to lower this energy barrier. Potential energy refers to the stored energy in a system due to its position or arrangement, and while it plays a role in chemical reactions, it does not specifically describe the energy needed to start the reaction. Free energy, on the other hand, relates to the amount of energy available to do work at constant temperature and pressure, and is more about the change in energy during the reaction rather than the initiation. Catalytic energy is not a standard term in chemistry; instead, catalysts lower the activation energy, making it easier for reactions to proceed, but they are not the energy needed to initiate the reaction by themselves.