An endothermic reaction The decomposition of sodium bicarbonate, (sodium hydrogen carbonate), used as in a dry powder fire extinguisher is a good example.
Although not chemical reactions, the processes of melting, and evaporation are endothermic processes.
The heat of the fire drives this reaction which absorbs heat and releases compounds which do not support combustion.
The dissolution of common salt and sugar in water are further example of endothermic processes.
When sodium thiosulfate dissolves in water the temperature of the liquid drops markedly.
When sodium thiosulfate crystallizes from a saturated solution, the temperature of the liquid rises markedly.
The footwarmers used in passenger trains of earlier years gave out heat as sodium thiosulfate crystallized from saturated solution.
