Endothermic reaction?

• A. A chemical reaction that absorbs energy.
• B. A chemical reaction that releases energy.
• C. A reaction that happens spontaneously.
• D. A reaction that occurs only at high pressure.

Answer: (A)

Endothermic means the reaction takes in energy from its surroundings, so heat flows into the system. This is shown by a positive enthalpy change (ΔH > 0). So describing a chemical reaction as one that absorbs energy fits the concept of endothermy.

In contrast, releasing energy describes exothermic reactions, where heat leaves the system. Spontaneity involves Gibbs free energy and can occur with either endothermic or exothermic heat changes depending on conditions, so it doesn’t define endothermicity. And endothermic behavior isn’t limited to high pressure; endothermic reactions can occur across a range of pressures.