Exothermic reaction

In Chimie a reaction is known as exothermic if it produces heat. This heat released brutally can contribute to the racing of the reaction which becomes then explosive. Many reactions implying of the acids or the bases are exothermic. The reaction can be violent. Thus a metal sodium fragment reacts violently with water, is not inserted there because of the intense gas release Hydrogène (flammable) accompanied by the caustic formation of soda (Hydroxyde of sodium) and of a strong heat emission which can ignite hydrogen (dangerous experiment).

Certain exothermic reactions, without being explosive, can discuss themselves as soon as they were started (rise in temperature supporting the reaction speed).

• It is the case of fermentation under the action of bacteria (see figure).

• It is the case also of the reduction of iron the Oxide by metal aluminum ( Aluminothermie), used by the railroads of the whole world to carry out the welding of the rails on the ground. The heat released is such as the temperature exceeds more 2000°C and that iron obtained is in the liquid state what dissolves the end of the two rails, thus ensuring a perfect welding.