What does endothermic mean?
Endothermic describes any chemical reaction or physical process that absorbs heat from its surroundings rather than releasing it. The word comes from Greek roots meaning "within" and "heat," and it entered scientific English in the late nineteenth century as thermodynamics matured into a rigorous discipline. Endothermic reactions are common in everyday life: an instant cold pack cools because dissolving its contents draws heat away from your hand, photosynthesis stores solar energy in sugar molecules, and baking bread involves changes that take in heat. Chemists identify such reactions by a positive enthalpy change, meaning the products hold more energy than the reactants did. The natural antonym is exothermic, which characterizes heat-releasing processes like combustion. Though technical in origin, endothermic is now standard vocabulary in science education worldwide.
adjectiveAbsorbing heat from the surroundings; describing a chemical reaction or physical process that takes in energy as heat rather than releasing it.
- (Of a chemical reaction or physical process) absorbing heat from its surroundings, typically accompanied by a fall in temperature.
- (Of an animal) warm-blooded; generating and maintaining internal body heat by metabolic means (used chiefly in the related forms 'endotherm' and 'endothermy').
"Photosynthesis is an endothermic process, drawing in energy from sunlight to build sugars from carbon dioxide and water."
"Dissolving ammonium nitrate in water is strongly endothermic, which is why instant cold packs feel icy to the touch."
"The decomposition of limestone into quicklime requires sustained heating because it is an endothermic reaction."
Cold packs stay cold because they're doing chemistry backwards — an endothermic reaction literally drinks heat out of your skin.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of endothermic
Endothermic combines the Greek prefix 'endo-' (from 'endon,' meaning within or inside), the root 'therm-' (from 'thermē,' heat), and the adjectival suffix '-ic.' It was formed in the nineteenth century alongside other thermo-dynamic terminology, paralleling its counterpart 'exothermic' (Greek 'exo-,' outside). It shares these Greek roots with words like thermal, thermometer, and thermostat, and the 'endo-' element appears in scientific terms such as endocrine and endogamy.
Related word forms
How endothermic is actually used
Endothermic is primarily a technical term found in chemistry, physics, and thermodynamics; it is formal in register but widely understood thanks to school science curricula. In zoology, the concept of internal heat generation is usually expressed with the noun forms 'endotherm' and 'endothermy' rather than the adjective itself.
Easily confused with endothermic
Exothermic reactions release heat to their surroundings, while endothermic reactions absorb heat from them.
An endotherm is a warm-blooded animal that generates its own body heat, whereas endothermic describes processes that absorb heat.