In this article, we consider the phenomenon of oxidation. This is a multicomponent concept that appears in various fields of science, for example, biology and chemistry. We will also get acquainted with the diversity of this process and its essence.
Introduction
From the basic and initial point of view, oxidation is a chemical process , which is accompanied by an increase in the degree of atomic oxidation of the substance that it undergoes. This phenomenon occurs due to the transfer of electrons from one atom (reducing agent and donor) to the second (acceptor and oxidizing agent).
This terminological unit was introduced into the circulation of chemistry at the beginning of the 19th century, and academician V.M. did it Severgin to create a sign indicating the interaction of substances with oxygen from atmospheric air.
In some cases, the oxidation of a molecule is accompanied by the creation of instability in the structure of a substance and leads to its decomposition into molecules with greater stability and small size. The fact is that this process can be repeated at several different levels of grinding. That is, a smaller particle formed can also have a higher oxidation state than atomic particles, which were the original in the same substance, but larger and more stable.
In chemistry, there is the concept of a lower and a higher degree of oxidation. This makes it possible to classify atoms as far as possible exhibiting this property. The highest oxidative degree corresponds to the number of the group in which the element is located. The lowest degree, as a rule, is determined by the correspondence of the even and odd numbers: the highest 8 = the lowest 2, the highest 7 = the lowest 1.
Combustion
Combustion is an oxidation process. In atmospheric air (as well as in pure oxygen) can be oxidized in the form of combustion. An example is a variety of substances: the simplest elements of substances of metals and non-metals, inorganic and organic compounds. However, the most practically significant is a combustible substance (fuel), among which the natural reserves of oil, gas, coal, peat, etc. are distinguished. Most often they form a complex mixture of hydrocarbons with a small fraction of oxygen, sulfur, nitrogen-containing compounds of the organic type, and inclusions of trace amounts of other elements.
Biological oxidation
In biology, oxidation reactions are processes that, taken together, converge to a change in the oxidation state of the atoms involved in the reaction, and this is due to the electronic distribution between the interacting components.
The first assumption is that in all living organisms the most complex chemical processes occur. reaction was put forward in the eighteenth century. The chemist from France A. Lavoisier studied the problem. He drew attention to the fact that the course of combustion and oxidation in biology are similar to each other.
Scientists have studied the way of oxygen that was absorbed by a living creature due to breathing. They reported that these oxidation processes are similar processes occurring at different rates. He drew attention to the decomposition process, which, as it turned out, is the phenomenon of the interaction of an oxygen molecule (oxidizer) with organic matter, which includes carbon and / or hydrogen atoms. Due to decomposition, an absolute transformation of the substance occurs.
There were moments of the process that scientists could not fully understand, among which the questions:
- For what reason is oxidation carried out in conditions of low body temperature, despite its presence outside the body, only at high temperature.
- For what reason, oxidation reactions are phenomena that are not accompanied by an outburst of flame, as well as huge releases of released energy.
- How is the "burning" of the nutrient series of substances in the body, if it is 80% (approximately), consists of a liquid - water H 2 O.
Types of biological oxidation
In accordance with the conditions of the environment in which the oxidation occurs, it is divided into two types. Most fungi and microorganisms obtain energy resources by converting a nutrient through an anaerobic method. This reaction occurs without access of molecular oxygen, and it is also called glycolysis.
A more complex way of converting nutrients is the aerobic form of biological oxidation or tissue respiration. The lack of oxygen causes the cells to fail to oxidize to produce energy, and they die.
Getting energy by a living organism
In biology, oxidation is a multi-component phenomenon:
- Glycolysis is the initial stage of heterotroph organisms, during which monosaccharides break down oxygen-free, and it precedes the onset of cellular respiration.
- Pyruvate oxidation - the conversion of pyruvic acid to acetyl coenzyme. These reactions are possible only with the participation of pyruvate dehydrogenase enzyme complexes.
- The decomposition of beta-fatty acids is a parallel phenomenon that occurs with the oxidation of pyruvate, the purpose of which is the conversion of each fatty acid to acetyl coenzyme. Further, this substance is supplied to the cycle of acids of the tricarboxylic group.
- The Krebs cycle is the conversion of acetyl coenzyme to citric acids and further exposure to subsequent conversion (dehydrogenation, decarboxylation and regeneration phenomena).
- Oxidative phosphorylation is the last stage of transformation during which the eukaryotic organism converts adenosine diphosphate into adenosine triphosphoric acids.
It follows from this that oxidation is a process that includes:
- the phenomenon of hydrogen cleavage from the substrate, which undergoes oxidation (dehydrogenation);
- the phenomenon of recoil of an electron by a substrate;
- the phenomenon of attachment of an oxygen molecule to a substrate.
Metal reaction
Oxidation of a metal is a reaction during which, through the interaction of an element from a group of metals and O2, the formation of oxides (oxides).
In a broad sense, a reaction in which an atom loses an electron and creates a variety of compounds, for example, substances of chlorides, sulfides, etc. In the natural state, most often metals can only be in a completely oxidized state (in the form of ore). For this reason, the oxidation process is presented as a reduction reaction of various components of the compound. Practically used substances of metals and their alloys, when interacting with the environment, gradually oxidize - they corrode. The processes of metal oxidation occur due to thermodynamic and kinetic factors.
Valency and oxidation
The oxidation state is valency. However, there is some difference between them. The fact is that valency chem. Element man determines the ability of the atom to establish a certain number of chemical bonds with other types of atoms. This is due to the presence of different types of atoms, respectively, a different ability to create a relationship. However, valency can only be in a covalent compound and is formed due to the creation of a common electron pair between the atoms. The degree of oxidation, in contrast to valency, is the degree of conditional charge that an atom of matter possesses. It can be positive "+", zero "0" and negative "-". Also, the oxidation state assumes that all bonds in the substance are ionic.
Reaction over water
More than two billion years ago, plant organisms took one of the most important steps towards the beginning of evolution. The process of photosynthesis began to take shape. However, only reduced hydrogen sulfide type substances were initially photooxidized, which were represented on earth in extremely small sizes. Oxidation of water is a process that has introduced a significant amount of molecular oxygen into the atmosphere. This allowed the bioenergy processes to move to a new aerobic level. The same phenomenon allowed the formation of an ozone screen that protects life on Earth.