Advanced Placement (AP) Biology Practice Exam

What characterizes an exergonic reaction?

1. Requires input of energy

2. Absorbs free energy from the surroundings

3. Releases free energy during a chemical reaction

4. Occurs only at high temperatures

The correct answer is: Releases free energy during a chemical reaction

An exergonic reaction is characterized by its ability to release free energy during a chemical reaction. This release of energy often occurs as the reactants transition into products that are more stable, meaning they possess lower Gibbs free energy. The decrease in free energy signifies that the reaction can proceed spontaneously under standard conditions, without the need for an external energy input. In contrast, a reaction that requires an input of energy, like an endergonic reaction, would not be classified as exergonic. Similarly, while exergonic reactions occur, they do not absorb free energy; that characteristic applies to processes that are endergonic. Lastly, the assertion that exergonic reactions occur only at high temperatures is misleading. While temperature can affect reaction rates, exergonic reactions can occur at various temperatures, depending on the specific reaction and conditions.