Which term describes energy required or absorbed as heat in a chemical reaction?

• A. Endothermic reaction
• B. Exothermic reaction
• C. Acid
• D. Base

Answer: (A)

Energy changes in chemical reactions can involve heat flowing into or out of the system. When a reaction absorbs heat from its surroundings, it is described as endothermic. This means the system takes in energy, often causing the surroundings to feel cooler, and the overall energy of the reacting substances increases (positive enthalpy change). Exothermic reactions, by contrast, release heat to the surroundings, warming them (negative enthalpy change). Acids and bases are about chemical properties and how substances react with others, not about heat transfer during a reaction, so they don’t describe this energy aspect. Since the question is specifically about energy required or absorbed as heat, the term that fits is endothermic reaction.