Can burn you chemically

Some combustion reactions create flames. What happens there chemically?



Forest fire © dpa

At the end of the 17th century, the doctor and chemist G. E. Stahl suspected a certain substance in all flammable substances. He called this one Phlogiston. When burned, phlogiston should escape and cause the fire phenomena.

The French A.L. In 1783 Lavoisier succeeded in clearing up the combustion process and refuting the phlogiston theory. He realized that a combustion is always the union of a substance with oxygen. According to the French word for oxygen "oxygèn" he called this reaction oxidation.

oxidation

Oxidation is a chemical reaction in which one of the reactants binds oxygen.

The type and speed of the reaction determine the amount of heat released. If, for example, a lot of heat is released in a short period of time, phenomena such as flames or embers can occur. A distinction is therefore made between:

- Oxidation without the appearance of fire (e.g .: oxidizing, rusting, fermenting, decaying ...) and
- Oxidation with the appearance of fire (e.g .: burning, exploding, detonating ...).

In combustion reactions, oxygen acts as an oxidizing agent and is reduced during the reaction itself, i.e. it absorbs electrons. The fuels, on the other hand, give off electrons, so they are oxidized.

Radical reaction

In combustion there is another type of reaction that usually takes place directly in the flame: the radical reaction. radical In chemistry, denote atoms, molecules or molecule fragments that have a special electron arrangement.

Such radicals arise when electron pair bonds are separated by the supply of energy - radicals therefore contain unpaired electrons. Since nature always strives to reach the lower energy state, in this case an electron pair bond, the radicals are very reactive and react with other radicals to form an electron bond. But they also have the ability to destroy existing bonds in other molecules and thus to form new radicals, which leads to a chain reaction.

However, radical reactions only take place at high temperatures or in the presence of a catalyst. In order to stop such reactions, i.e. to put out the fire, so-called Inhibitors used. These are radical scavengers that interrupt the chain reaction by intercepting the intermediate products and rendering them harmless.