Which statement best describes the energy change when ATP is hydrolyzed to ADP and inorganic phosphate?

• A. Endergonic
• B. Isothermal
• C. Exergonic
• D. Isometric

Answer: (C)

Energy release during ATP hydrolysis drives cellular work. When ATP is converted to ADP and inorganic phosphate, the bonds between the phosphate groups are broken, and the resulting products are at a lower energy level and have more resonance stabilization. This makes the reaction energetically favorable, with a negative ΔG, so it is exergonic. The released energy can then be coupled to endergonic reactions to power them. The other options aren’t describing the thermodynamics of this reaction: it’s not about temperature changes (isothermal) or about a constant-length constraint (isometric); the key point is that energy is released (exergonic).