An endothermic reaction is one that:

Question

Accepted Answer

Absorbs heat from the surroundings. An endothermic reaction is one that absorbs heat energy from the surroundings. During an endothermic reaction, the products have higher energy content than the reactants, and the energy difference is absorbed from the environment as heat. This causes the surroundings to feel cooler. Common examples include photosynthesis (which absorbs light energy), the dissolution of ammonium nitrate in water (used in cold packs), and the thermal decomposition of calcium carbonate.

A reaction that releases heat to the surroundings is exothermic, the opposite of endothermic. All chemical reactions involve energy changes of some kind; there are no reactions with absolutely zero energy change. Endothermic reactions can occur at various temperatures, not only at very high temperatures, though some require an initial energy input to get started. The temperature at which a reaction occurs depends on the specific reaction and conditions, not on whether it is endothermic or exothermic.

Understanding the energy changes in chemical reactions is fundamental to chemistry and is tested on the CLEP Natural Sciences exam. In endothermic reactions, the enthalpy change (ΔH) is positive (energy is absorbed), while in exothermic reactions, ΔH is negative (energy is released). This concept connects to thermodynamics, kinetics, and practical applications like energy production, industrial chemistry, and biological metabolism.

CLEP Natural Sciences: Question of the Day

Get a free CLEP Natural Sciences question every day

Ready for the full CLEP Natural Sciences? Earn 6 college credits.