Definition of exothermic in US English:



  • 1(of a reaction or process) accompanied by the release of heat.

    The opposite of endothermic (sense 1)
    • ‘For these exothermic processes, the solubility decreases with an increase in temperature.’
    • ‘Sodium hydroxide dissolved into water is an exothermic process, ammonium nitrate dissolved in water is an endothermic process.’
    • ‘Inside the mold, the liquid undergoes an exothermic chemical reaction, which forms the polyurethane polymer in the mold.’
    • ‘When fireworks are ignited, the chemical compounds react with each other in an exothermic reaction - releasing energy.’
    • ‘The rusting of iron is an exothermic reaction and this process is used in hand warmers which are utilized in cold regions.’
    1. 1.1 (of a compound) formed from its constituent elements with a net release of heat.
      • ‘Little heat is needed in the roasting of sulfide ores because the oxidation of the sulfide ion to sulfur dioxide is exothermic.’


Late 19th century: from French exothermique.