Which statement correctly describes an endothermic reaction?

• A. It absorbs energy in the form of heat and requires additional heat input to continue.
• B. It releases energy as heat and becomes self-sustaining.
• C. It neither absorbs nor releases heat.
• D. It only occurs in gaseous systems.

Answer: (A)

Endothermic reactions draw energy from their surroundings. The reacting system gains energy, so the overall energy change is positive and heat must flow into the reaction to keep it going. That’s exactly what the statement describes: energy is absorbed in the form of heat and additional heat input is needed to continue. In real life, this shows up when surroundings feel cooler as heat moves into the reaction.

Think of examples like photosynthesis, where plants absorb sunlight to power building sugars, or dissolving certain salts in water that causes the solution to feel cooler because heat is being absorbed. This contrasts with exothermic processes, which release heat, and with the notion that heat involvement is confined to gases or that no heat is exchanged at all (both of which aren’t true for endothermic reactions).