An exergonic reaction is

• A. A chemical reaction that releases energy
• B. A chemical reaction that stores energy
• C. A chemical reaction that never changes energy
• D. A chemical reaction that absorbs energy

Answer: (A)

Exergonic reactions release free energy as they proceed, moving from a higher-energy state of reactants to a lower-energy state in the products. Because the products have less free energy than the reactants, the change in free energy (ΔG) is negative, so the reaction can occur spontaneously and can supply energy to power other cellular processes. This energy release is the hallmark of exergonic reactions; it often drives work in the cell, like powering endergonic reactions or motor activities.

Storing energy or absorbing energy would require input to raise the system’s free energy, which corresponds to endergonic processes with a positive ΔG. A reaction that never changes energy would have ΔG near zero, not an exergonic process.