Often from decent-looking people you can hear about the dangers to the health of a product or tool. Moreover, the main argument in favor of such a statement will be the phrase: "This is chemistry!" However, only those who clearly skipped classes in this subject can say this at school. The fact is that the human, and indeed any biological organism, in itself consists of many organic and inorganic substances. At the same time, various processes that continuously occur inside it help to maintain its viability. One of the main among them is the chemical decomposition reaction. Let's find out more about her and the features of its course with organic and inorganic substances.
What kind of process is called a chemical reaction
First of all, it is worth knowing the meaning of the term “chemical reaction”. This phrase means the conversion of one or more source substances (called reagents) into others. In the process of such a metamorphosis, the nuclei of the atoms of the interacting compounds are not susceptible to change, but the redistribution of electrons occurs. Thus, after conversion, new atomic compounds are formed at the output.
Chemical reactions have a qualitative difference from physical and nuclear.
- As a result of the former, the starting reagents never change their composition, although they are capable of forming mixtures or passing from one state of aggregation to another. In contrast, chemical processes are accompanied by the formation of new compounds with completely different properties.
- The second result is a change in the isotopic composition and number of atoms. Thus, at the exit of some elements, others are formed. However, for chemical processes, such deep metamorphoses are not characteristic. Since the changes that have occurred because of them do not affect the internal structure of atoms.
Chemical reaction conditions
In many cases, for the successful occurrence of processes of this kind, it is necessary simply to physically contact the reactants with each other or mix them. But often, to start a chemical reaction, she needs catalysts. Various substances and certain external conditions can play this role.
- The effect of temperature. In order to start separate chemical processes, it is necessary to heat the reagents. For example, in order to start the decomposition reaction of calcium carbonate, this temperature of this compounds must be increased to 900-1200 ° C.
- Electromagnetic waves. The most effective stimulating course of any processes is exposure to reagents by light waves. Such reactions are called "photochemical". A classic example of such a reaction is photosynthesis.
- Ionizing radiation.
- Exposure to electric current.
- Various kinds of mechanical effects on reactants.
What types of chemical reactions exist
Classification of such processes is mainly carried out on six grounds.
- By the presence of a phase separation boundary: homo / heterogeneous reactions.
- On the release / absorption of heat: exothermic and endothermic processes.
- By the presence / absence of catalysts: catalytic and non-catalytic reactions.
- In the direction of flow: reversible and irreversible processes. Depending on this category is the type of sign between the left and right sides of the chemical equation. For irreversible - these are two arrows directed in opposite directions, for reversible - only one, directed from left to right.
- By changing the degree of oxidation. According to this principle, a redox reaction is isolated.
- Decomposition (splitting), compound, substitution and exchange are types of chemical processes according to the type of metamorphosis of reagents.
The decomposition reaction (splitting): what is it
This term refers to the process by which one complex substance is divided into two or more simple ones. In most cases, the catalyst for this is high temperature. For this reason, this process is also called the thermal decomposition reaction.
As an example, one of the classical methods for producing pure oxygen (O 2 ) in industry can be cited. This occurs as a result of heating KMnO 4 (better known to everyone under the household name "potassium permanganate").
As a result of the splitting, not only oxygen is formed, but also potassium manganate (K 2 MnO 4) , as well as manganese dioxide (MnO 2).
The decomposition reaction equation
Any chemical equation consists of two parts: left and right. In the first of these, reacting compounds are recorded, and in the second, reaction products. A right-pointing arrow is usually placed between them. Sometimes it is two-way, when it comes to a reversible process. In some cases, it is permissible to replace it with an equal sign (=).
The process under consideration, like other types of chemical processes, has its own formula. Schematically, the equation of the decomposition reaction looks like this: AB (t) → A + B.
It is worth remembering that the vast majority of such processes occur under the influence of heat. To report this, either the letter t or the triangle is often placed above or next to the arrow. However, sometimes instead of heat, various substances, radiation, act as catalysts.
In the above formula, AB is the initial complex compound, A, B are new substances formed as a result of the decomposition reaction.
Practical examples of such a process are very common. This formula can be illustrated using the process equation described in the previous paragraph: 2KMnO 4 (t) → K 2 MnO 4 + MnO 2 + O 2 ↑.
Types of decomposition reactions
Several types of decomposition are distinguished depending on the type of catalyst (which facilitates the splitting of the complex substance into simpler ones).
- Biodegradation - the decomposition of substances due to the activity of living organisms (microorganisms, fungi, algae). In simpler terms, this process can be called decay. It is because of it that the products deteriorate. On the one hand, this prevents their long storage, on the other, it helps nature to utilize all unnecessary, thus restoring ecosystems.
- Radiolysis - the decomposition of compounds by exposure to their molecules by ionizing radiation.
- Thermolysis is an increase in temperature in order to start the decomposition reaction (examples of such processes can be found in paragraphs 8-9).
This type of splitting has a subspecies - pyrolysis. It differs from ordinary thermolysis in that, in addition to the effect of high temperature on the molecules of a substance, they are also deprived of the opportunity to interact with oxygen (O 2 ). - Solvolysis is the exchange decomposition between a solute and the solvent itself. Depending on the type of the latter, such types of this process are distinguished: hydrolysis (water), alkolysis (alcohols), ammonolysis (ammonia).
- Electrolysis is the decomposition of molecules by applying an electric current to them (an example in the next paragraph).
H2O cleavage
Having dealt with the theory regarding the decomposition reaction, practical examples of its implementation are worth considering. Since H 2 O is today one of the most accessible substances for conducting chemical experiments, it is worth starting with it.
This water decomposition reaction is also called electrolysis and looks like this: 2 2 (electric current) → 2 2 ↑ + 2 ↑.
This equation is deciphered as follows: under the influence of electric current on water molecules, they split and form two gases - oxygen and hydrogen.
It is worth noting that this method is actively used in submarines to produce oxygen. In the modern world, he has replaced a more expensive way to obtain this vital substance from sodium peroxide (Na 2 O 2) , using its interaction with carbon dioxide: Na 2 O 2 + CO 2 ↑ → Na 2 CO 3 + O 2 ↑.
In the long term, the decomposition of water can be of great importance for the future of the planet. Since in this way it is possible to produce not only oxygen, but also hydrogen, which is used as rocket fuel. Development in this area has been ongoing for many years, but the main problem is the need to reduce the amount of energy spent on the breakdown of water molecules.
H2O2 cleavage
Among other examples of the decomposition reaction, attention is paid to the formation of water and oxygen from hydrogen peroxide (peroxide).
It looks like this: 2 2 (t) → 2 2 + 2 ↑.
This process is also thermal, because to start it, it is necessary that the starting material be heated to a temperature of 150 ° C.
It is for this reason that hydrogen peroxide (which most people use to treat wounds) does not turn into water while standing in first-aid kits.
However, it is worth remembering that the decomposition of hydrogen peroxide can also occur at ordinary room temperature if the substance is in contact with compounds such as caustic soda (NaOH) or manganese dioxide (MnO 2 ). Also, platinum (Pt) and cuprum (Cu) can act as catalysts.
The thermal decomposition of CaCO3
Another interesting example is the breakdown of calcium carbonate. This process can be written using the following equation: CaCO 3 (t) → CaO + CO 2 ↑.
The product of this reaction will be quicklime (calcium oxide) and carbon dioxide.
The above process is actively used in industry to produce carbon dioxide. Similar reactions are carried out in specialized mines, since the decomposition of calcium carbonate occurs only at temperatures from 900 ° C.