Decomposition reactions play a large role in the life of the planet. After all, they contribute to the destruction of waste products of all biological organisms. In addition, this process daily helps the human body to assimilate various complex compounds by splitting them into simple ones (catabolism). In addition to all of the above, this reaction promotes the formation of simple organic and inorganic substances from complex ones. Let's learn more about this process, and also look at practical examples of the chemical decomposition reaction.
What are called reactions in chemistry, what types of them are and what they depend on
Before studying decomposition information, it is worth learning about chemical processes in general. By this name is meant the ability of the molecules of some substances to interact with others and to form new compounds in this way.
For example, if oxygen and two hydrogen molecules interact with each other , the result will be two molecules of hydrogen oxide, which we all know as water. This process can be written using the following chemical equation: 2 2 ↑ + 2 ↑ → 2 2 .
Although there are different criteria by which chemical reactions are distinguished (thermal effect, catalysts, presence / absence of phase boundaries, change in the oxidation state of reagents, reversibility / irreversibility), they are most often classified according to the type of conversion of interacting substances.
Thus, four types of chemical processes are distinguished.
- Compound.
- Decomposition.
- Exchange.
- Substitution.
All of the above reactions are graphically written using equations. Their general scheme looks like this: A → B.
The starting reagents are on the left side of this formula, and the substances formed as a result of the reaction are on the right. As a rule, to start it, exposure to temperature, electricity, or the use of catalytic additives is necessary. Their presence should also be indicated in the chemical equation.
What is the decomposition reaction (cleavage)
This type of chemical process is characterized by the formation of two or more new compounds from molecules of one substance.
In simpler terms, the decomposition reaction can be compared to a house from the designer. Having decided to build a typewriter and a boat, the child dismantles the initial structure and constructs the desired from its details. At the same time, the structure of the designer elements themselves does not change, just as it does with the atoms of the substance involved in the splitting.
What is the equation of the reaction in question?
Despite the fact that hundreds of compounds are capable of separating a complex substance into simpler components, all similar processes occur on the same principle. You can depict it using the schematic formula: ABV → A + B + C.
In it, ABV is the initial compound that has undergone cleavage. A, B and C are substances formed from ABV atoms during the decomposition reaction.
Types of cleavage reactions
As mentioned above, in order to start a chemical process, it is often necessary to have a certain effect on the reagents. Depending on the type of such stimulation, several types of decomposition are distinguished:
- Biodegradation (biodegradation). Its essence lies in the decay of more complex compounds into simple ones under the influence of living organisms (microorganisms). An illustration of this process can be rotting or decomposition of garbage.
- Thermolysis refers to the breakdown of substances under the influence of high temperatures. This species has a subspecies - pyrolysis. In the decomposition reaction of this kind for its conduct, the substances are not only heated, but also deprived of access of oxygen and other oxidizing agents to them.
- Electrolysis refers to the splitting of compounds using electric current.
- Radiolysis - the decomposition of a substance under the influence of ionizing radiation. By the way, this process is actively used in radiation therapy.
- Solvolysis - this reaction can be considered the boundary between decomposition and metabolism (AB + HB → AG + BV). Although it leads to the cleavage of complex compounds into simple ones under the influence of a solvent, the released atoms of the initial reagent interact not only with each other, but also with the catalyst. Depending on its nature, three subspecies of solvolysis are distinguished: alcoholysis (alcohols - ROH), hydrolysis (water - H 2 O) and ammonolysis (ammonia - NH 3 ).
The decomposition of potassium permanganate (KMnO4)
Having dealt with the theory, it is worth considering practical examples of the process of splitting substances.
The first of these will be the decay of KMnO 4 (commonly referred to as potassium permanganate in the common people) due to heating. The equation for the decomposition reaction of potassium permanganate is as follows: 2KMnO 4 (t 200 ° ) → K 2 MnO 4 + MnO 2 + O 2 ↑.
From the presented chemical formula it is seen that to activate the process it is necessary to heat the initial reagent to 200 degrees Celsius. For a better reaction, potassium permanganate is placed in a vacuum vessel. From this we can conclude that this process is pyrolysis.
In laboratories and in production, it is carried out to obtain clean and controlled oxygen.
Thermolysis of Potassium Chlorate (KClO3)
The decomposition of bertollet salt is another example of pure thermolysis.
The mentioned process goes through in two stages and looks like this:
- 2 KClO 3 (t 400 ° ) → 3KClO 4 + KCl.
- KClO 4 (t from 550 ° ) → KCl + 22
Also, the thermolysis of potassium chlorate can be carried out at lower temperatures (up to 200 ° C) in one stage, but for this it is necessary that catalyzing substances - oxides of various metals (cuprum, ferum, manganese, etc.) take part in the reaction.
An equation of this kind will look like this: 2KClO 3 (t 150 ° , MnO 2 ) → KCl + 2 2 .
Like potassium permanganate, bertoletova salt is used in laboratories and industry to produce pure oxygen.
Electrolysis and radiolysis of water (H20)
Another interesting practical example of the reaction in question is the decomposition of water. It can be produced in two ways:
- Under the influence of electric current on hydrogen oxide: 2 → 2 ↑ + 2 ↑. The considered method of producing oxygen is used by submariners on their submarines. Also in the future they plan to use it to produce hydrogen in large quantities. The main obstacle to this today is the huge energy costs necessary to stimulate the reaction. When a way is found to minimize them, the electrolysis of water will become the main way to produce not only hydrogen, but also oxygen.
- It is possible to split water even when exposed to alpha radiation: H 2 O → H 2 O + + e - . As a result, the hydrogen oxide molecule loses one electron, being ionized. In this form, H2O + again reacts with other neutral water molecules, forming a highly reactive hydroxide radical: 2 + 2 + → 2 + . The lost electron, in turn, also reacts in parallel with neutral molecules of hydrogen oxide, contributing to their decay into radicals H and OH: H 2 O + e - → H + OH.
Alkane Cleavage: Methane
Considering various methods of separation of complex substances, it is worth paying special attention to the decomposition of alkanes.
Under this name are saturated hydrocarbons with the general formula C X H 2X + 2. In the molecules of the substances under consideration all carbon atoms are connected by single bonds.
Representatives of this series are found in nature in all three aggregate states (gas, liquid, solid).
All alkanes (the decomposition reaction of representatives of this series are lower) are lighter than water and do not dissolve in it. However, they themselves are excellent solvents for other compounds.
Among the main chemical properties of such substances (combustion, substitution, halogenation, dehydrogenation) - and the ability to break down. However, this process can occur both fully and partially.
The above property can be considered by the example of the methane decomposition reaction (the first member of the alkane series). This thermolysis occurs at 1000 ° C: CH 4 ↑ → C + 2H 2 ↑ .
However, if the methane decomposition reaction is carried out at a higher temperature (1500 ° C), and then it is sharply reduced, this gas does not completely decompose, forming ethylene and hydrogen: 2CH 4 ↑ → C 2 H 4 ↑ + 3H 2 ↑.
Ethane decomposition
The second member of the alkane series under consideration is C 2 H 4 (ethane). Its decomposition also occurs under the influence of high temperature (50 ° C) and in the complete absence of oxygen or other oxidizing agents. It looks like this: C 2 H 6 ↑ → C 2 H 4 ↑ + H 2 ↑ .
The above equation for the decomposition of ethane to hydrogen and ethylene cannot be considered pure pyrolysis. The fact is that this process occurs with the presence of a catalyst (for example, nickel metal Ni or water vapor), and this contradicts the definition of pyrolysis. Therefore, it is correct to speak of the decomposition example presented above as a decomposition process that occurs during pyrolysis.
It is worth noting that the reaction considered in industry is widely used to obtain the world's most produced organic compound - ethylene gas. However, due to the explosion hazard, C 2 H 6 more often this simplest alkene is synthesized from other substances.
Having examined the definitions, equation, types and various examples of the decomposition reaction, we can conclude that it plays a very large role not only for the human body and nature, but also for industry. Also, with its help, laboratories manage to synthesize many useful substances, which helps scientists conduct important chemical studies.