Types of chemical reactions

In modern science, chemical and nuclear reactions that occur as a result of the interaction of the initial substances, which are called reagents, are distinguished. As a result, other chemicals are formed, which are called products. All interactions occur under certain conditions (temperature, pressure, light, radiation, the presence of catalysts, etc.). The nuclei of atoms of reagents of chemical reactions do not change. In nuclear transformations new nuclei and particles are formed. There are several different signs that determine the types of chemical reactions.

As a basis for classification, one can take the number of initial and formed substances. In this case, all types of chemical reactions are divided into five groups:

1. Decomposition (several new ones are obtained from one substance), for example, decomposition of potassium chlorate on potassium chloride and oxygen: KCLO3 → 2KCL + 3O2.
2. Compounds (two or more compounds form one new), interacting with water, calcium oxide is converted to calcium hydroxide: H2O + CaO → Ca (OH) 2;
3. Substitutions (the number of products is equal to the number of initial substances in which one constituent is substituted for another), iron in copper sulfate replacing copper forms ferrous sulfate: Fe + CuSO4 → FeSO4 + Cu.
4. Double exchange (the molecules of two substances are exchanged by leaving parts of them), metals in potassium iodide and silver nitrate exchange anions, forming a precipitating silver iodide and nitric acid cadium: KI + AgNO3 → AgI ↓ + KNO3.
5. Polymorphic transformation (the substance changes from one crystalline form to another), red mercuric iodide turns to yellow mercury iodide: HgI2 (red) ↔ HgI2 (yellow).

If the chemical transformations are considered on the basis of a change in the reacting substances of the degree of oxidation of the elements, then the types of chemical reactions can be divided into groups:

1. With a change in the degree of oxidation, oxidation-reduction reactions. As an example, we can consider the interaction of iron with hydrochloric acid: Fe + HCL → FeCl2 + H2, as a result, the degree of oxidation of iron (the reducing agent that transfers electrons) has changed from 0 to -2, and hydrogen (an oxidizer taking electrons) from +1 to 0 .
2. Without changing the degree of oxidation, for example, the reaction of acid-base interaction of hydrogen bromide with sodium hydroxide: HBr + NaOH → NaBr + H2O, as a result of such reactions salt and water are formed, and the oxidation states of the chemical elements entering into the starting materials do not change.

If we consider the chemical equilibrium and the rate of flow in the forward and reverse directions, then all types of chemical reactions can also be divided into two groups:

1. Reversible - those that simultaneously flow in two directions. Most reactions are reversible. An example is the dissolution of carbon dioxide in water to form unstable carbonic acid, which decomposes into the starting materials: H2O + CO2 ↔ H2CO3.
2. Irreversible - flow only in the forward direction, after a complete expenditure of one of the initial substances are completed, after which only the products and the initial substance taken in excess are present. Usually one of the products is either precipitated by an insoluble substance or a liberated gas. For example, in the interaction of sulfuric acid and barium chloride: H2SO4 + BaCl2 + → BaSO4 ↓ + 2HCl, insoluble barium sulfate precipitates .

Types of chemical reactions in organic chemistry can be divided into four groups:

1. Replacement (some atoms or groups of atoms are replaced by others), for example, when chloroethane reacts with sodium hydroxide, ethanol and sodium chloride are formed: C2H5Cl + NaOH → C2H5OH + NaCl, that is, the chlorine atom is replaced by a hydrogen atom.
2. Accession (two molecules react and form one), for example, bromine is attached at the point of rupture of the double bond in the ethylene molecule: Br2 + CH2 = CH2 → BrCH2-CH2Br.
3. Cleavage (the molecule decomposes into two or more molecules), for example, under certain conditions, ethanol decomposes into ethylene and water: C2H5OH → CH2 = CH2 + H2O.
4. The rearrangement (isomerization, when one molecule turns into another, but the qualitative and quantitative composition of the atoms in it does not change), for example, 3-chlorotene-1 (C4H7CL) turns into 1 chlorobutene-2 (C4H7CL). Here, the chlorine atom passed from the third carbon atom in the hydrocarbon chain to the first, and the double bond connected the first and second carbon atoms, and then began to connect the second and third atoms.

Other types of chemical reactions are known:

1. According to the thermal effect: reactions taking place with absorption (endothermic) or heat release (exothermic).
2. By the type of reactant reagents or products. Interaction with water - hydrolysis, with hydrogen - hydrogenation, with oxygen - oxidation or combustion. Cleavage of water - dehydration, hydrogen - dehydrogenation and so on.
3. According to the interaction conditions: in the presence of catalysts (catalytic), under the influence of low or high temperature, with a change in pressure, in the light and so on.
4. By the mechanism of the reaction: ionic, radical-chain or chain reactions.