Which term describes a reaction that releases free energy?

• A. Endergonic reaction
• B. Exothermic reaction
• C. Exergonic reaction
• D. Catabolic reaction

Answer: (C)

Think in terms of free energy change. A reaction that releases free energy has a negative Gibbs free energy change, meaning it can occur on its own and can do work for the cell. The label for this is exergonic. It’s the precise term that describes energy being released in the form of usable free energy.

Endergonic reactions require an input of energy, so they store energy rather than release it. Exothermic refers to heat released, but that's about heat flow, not the overall free-energy change; an exergonic reaction can release energy as work and isn’t defined strictly by heat output. Catabolic describes the type of metabolic pathway that breaks down complex molecules, often releasing energy, but it’s about process direction, not the specific energy change per se.