An endothermic change or reaction is one in which heat energy is taken in from the surroundings. Because the heat energy leaves the surroundings, their temperature falls. A thermometer placed in the reacting solution shows a temperature fall, and the container feels cold.
Thermal decomposition, such as heating calcium carbonate, is endothermic because it needs a constant supply of heat energy. Dissolving ammonium nitrate in water is also endothermic, which is why the water gets colder. Some sports injury cold packs use this kind of change. Melting and evaporating are endothermic changes too.
