What are the effects of the chemical reaction



 

The oxidation (or oxidation) is a chemical reaction in which a substance to be oxidized (electron donor) releases electrons. Another substance (oxidizing agent) takes up the electrons (electron acceptor). This is reduced by the electron uptake. Oxidation is therefore always associated with a reduction. Both reactions together are viewed as partial reactions of a redox reaction.

Oxidation:
Substance A releases an electron.
Reduction:
The electron is absorbed by substance B.
Redox reaction:
Substance A donates an electron to substance B.

 

history

The term oxidation was originally coined by Antoine Laurent de Lavoisier, who wanted to describe the union of elements and chemical compounds with the element oxygen (Oxygenium French: oxygene), i.e. the formation of oxides. The term was later expanded to include reactions in which hydrogen atoms were removed from a compound (dehydrogenation). On the basis of the ion theory and Bohr's atomic model, the oxidation could finally be interpreted and generalized from the point of view of electron theory. The characteristic of this process is now seen in the electron release of a chemical substance. In the past, oxidation was known as calcination.

Oxidation by oxygen

 

Original meaning and extension of the term

Oxidation in the original sense used to be the chemical reaction of a substance with oxygen. But even today this term is often associated with the conversion with oxygen and the formation of oxides. However, in the context of the more general definition, this reaction is only one of many that can be explained with the help of the valence electron theory.

Reacts e.g. B. a metal atom with an oxygen atom, one can understand the oxidation of the metal and thus the metal oxide formation using the following reaction equations:

Oxidation:
Oxidation: The metal M gives off two electrons.
Reduction:
Oxygen (O) accepts two electrons.
Redox reaction:
Oxygen oxidizes the metal and is itself reduced in the process.

In this case, oxygen tends to build up a stable valence electron shell with a total of eight electrons by absorbing two electrons (octet rule). The metal, in turn, can dissolve partially occupied shells by releasing the electrons and thus reach the next lower stable electron configuration.

Examples of oxidation by oxygen

  • Classic examples of oxidation by oxygen are all types of combustion of carbon-containing substances under atmospheric oxygen, e.g. combustion of coal, wood, gasoline in engines, candles, etc. Starting from coal (pure carbon), each carbon atom gives four electrons to two oxygen- Atoms to form two double bonds. Carbon dioxide (CO2).
Carbon + oxygen → carbon dioxide
  • In the body, food is transformed into endogenous substances, carbon dioxide (CO2) and water oxidizes. Not only in vivo, also in vitro Organic substances can react with oxygen in a variety of ways: A primary alcohol (alkanol) is gently oxidized. In the process, an aldehyde (alkanal) is formed first, and when it is oxidized again, a carboxylic acid (alkanoic acid) is formed. If the oxidation is violent, the step to the aldehyde can be skipped. If a secondary alcohol is oxidized, a ketone (alkanone) is formed. Tertiary alcohols cannot be oxidized because of their three carbon bonds.
  • Iron rusts (corrodes) under the influence of oxygen and forms various iron oxides (rust: Fe2O3, Fe3O4, FeO).
  • The reaction of hydrogen with oxygen (oxyhydrogen) produces hydrogen oxide, better known as water (H.2O):
Hydrogen + oxygen → water

Oxidation without oxygen

The term oxidation was later expanded to include reactions that follow the same chemical principle, even if no oxygen is involved. In a broader sense, oxidation means giving up electrons. For example, when sodium and chlorine react to form sodium chloride, the sodium atom donates an electron to the chlorine atom, so sodium is oxidized. In return, chlorine is reduced.

Oxidation partial reaction:
Sodium gives off an electron.
Partial reaction reduction:
In return, chlorine is reduced by absorbing an electron.
Overall reaction:
Sodium and chlorine react with each other in a redox reaction.

Since chlorine is only molecularly known as Cl2 goes into the reaction, one writes more precisely

Oxidation number

The oxidation number is defined as the hypothetical charge number of an atom or a group of atoms (molecule). During the oxidation, the oxidation number is increased (Na0 → Well+ I), decreased in the reduction.

In a molecule, the binding electron pair (s) is / are assigned to the atom whose electronegativity is higher. Numbers of similar atomic compounds are divided equally among each other. Ions have their charge number as the sum of their oxidation numbers, molecules the sum 0. The oxidation numbers of those atoms that are part of a functional group are important.

Oxidation in Biology

In biology in particular, oxidation is defined as the "release of hydrogen". In many biochemical processes in the cell, e.g. In glycolysis, for example, hydrogen atoms are “torn away” from organic compounds by certain coenzymes (NAD, NADP, FAD).

see also

Category: Chemical reaction