Which statement describes an endothermic reaction?

• A. The products are at a higher energy level than the reactants.
• B. The products are at a lower energy level than the reactants.
• C. The reaction releases energy to the surroundings.
• D. The reaction occurs without energy input.

Answer: (A)

Endothermic reactions absorb energy from their surroundings, so the energy content of the products ends up higher than that of the reactants. That makes the statement about the products being at a higher energy level the correct description of an endothermic process. If the products were at a lower energy than the reactants, energy would be released to the surroundings, which is characteristic of an exothermic reaction. Saying the reaction releases energy to the surroundings describes that exothermic behavior, not endothermic. And a process described as occurring without energy input would not fit endothermic, since endothermic reactions require energy to be absorbed.