And steel classification

- quality;

- chemical composition;

- appointment;

- microstructure;

- strength.

Steel quality

By chemical composition

carbon steels permanent impurities

Table 1.3.

CARBON STEEL

alloying elements additives or additives

Alloy steels low-alloyed(up to 2.5 wt.%), doped(from 2.5 to 10 wt.%) and highly alloyed "chrome"

According to the purpose of steel

Structural low-( or few-) And medium carbon.

instrumentalhigh carbon.

And (with special properties - ).

And

And increased heat resistance fast cutting steels.

ordinary quality,

Structural steels,

tool steel,

6) bearing (ball bearing) become,

7) high speed steel(high-alloyed, high-quality tool steels with a high tungsten content).

8) automatic, i.e.increased (or high) machinability, become.

An analysis of the composition of historically established marking groups of steels shows that the marking systems used make it possible to encode five classification features, namely: quality, chemical composition, purpose, degree of deoxidation, as well as way to get blanks(automatic or, in rare cases, foundries). The connection between marking groups and steel classes is illustrated in the lower part of the block diagram in Fig. 1.

SYSTEM OF MARKING GROUPS, MARKING RULES AND EXAMPLES OF STEEL GRADES

CARBON	REGULAR QUALITY
	steel group	Delivery guarantee	STAMPS
BUT	by chemical composition	St0	St1	St2	StZ	St4	St5	St6
B	by mechanical properties	Bst0	Bst1	Bst2	BSTZ	Bst4	Bst5	Bst6
IN	mechanical properties and chemical composition	ESPO	VST1	VST2	VSTZ	VST4	VST5	VST6
Carbon concentration, wt. %	0,23	0,06-0,12	0,09-0,15	0,14-0,22	0,18-0,27	0,28-0,37	0,38-0,49
QUALITY HIGH QUALITY	STRUCTURAL	EXAMPLES OF STAMPS
Grade: two-digit number of hundredths of a percent of carbon + an indication of the degree of deoxidation	05 08kp 10 15 18kp 20A 25ps ZOA 35 40 45 50 55 ... 80 85 Notes: 1) the absence of an indicator of the degree of deoxidation means “sp”; 2) "A" at the end of the grade indicates that the steel is high quality
INSTRUMENTAL	STAMPS
Brand: symbol "U" + number TETHS OF A PERCENTAGE OF CARBON	U7 U7A U8 UVA U9 U9A U10 U10A U12 U12A
ALLOYED	HIGH QUALITY HIGH QUALITY EXTRA HIGH QUALITY	STRUCTURAL	EXAMPLES OF STAMPS
Grade: two-digit number of HUNDREDTHS of a percentage of carbon + symbol of an alloying element + whole number of its percent	09G2 10KhSND 18G2AFps 20Kh 40G 45KhN 65S2VA 110G13L 2) brand 110G13L - one of the few in which the number of hundredths of a percent of carbon is three-digit
INSTRUMENTAL	EXAMPLES OF STAMPS
Grade: number of TENSES of percent carbon + alloying element symbol+ whole number of its percent	ZKh2N2MF 4KhV2S 5KhNM 7X3 9KhVG X KhV4 9Kh4MZF2AGST-SH 2) "-SH" at the end of the brand shows that the steel is of especially high quality, obtained, for example, by the method electroslag remelting (but not only)

Carbon structural steels of ordinary quality

Specific steels of the specified marking group are designated using a two-letter combination "St" which is the key (backbone) in the considered marking group. The steel grades of this group are immediately recognizable by this symbol.

The symbol "St" without a space is followed by a number indicating room brands from «0» before "6".

An increase in the grade number corresponds to an increase in the carbon content in steel, but does not indicate its specific value. Permissible limits of carbon concentration in steels of each grade are shown in Table. 1.5. Carbon content in ordinary carbon steels does not exceed 0.5 wt.%. Such steels are hypoeutectoid according to the structural criterion, and, therefore, structural according to their purpose.

After the number, one of three letter combinations follows: “kp”, “ps”, “sp”, indicating the degree of steel deoxidation.

The symbol "St" may be preceded by capital letters "A", "B" or "C", or there may be no symbols. In this way, information is transmitted about steel belonging to one of the so-called "delivery groups": A, B or IN, - depending on which of the normalized indicators of steel is guaranteed by the supplier.

Steel group BUT comes with a guarantee of the chemical composition, or the permissible values ​​​​of the concentration of carbon and impurities specified by GOST. The letter "A" is often not put on the stamp and its absence default stands for chemical composition guarantee. The consumer of steel, having no information about the mechanical properties, can form them by appropriate heat treatment, the choice of modes of which requires knowledge of the chemical composition.

Steel group B comes with a guarantee of the required mechanical properties. The consumer of steel can determine its optimal use in structures by the known characteristics of mechanical properties without prior heat treatment.

Steel group IN comes with a guarantee of both chemical composition and mechanical properties. It is used by the consumer mainly to create welded structures. Knowledge of the mechanical properties makes it possible to predict the behavior of the loaded structure in areas far from the welds, and knowledge of the chemical composition makes it possible to predict and, if necessary, correct the mechanical properties of the welds themselves by heat treatment.

Stamp Recording Examples ordinary quality carbon steel look like this: Vst3ps, Bst6sp, St1kp .

Ball bearing steels

Steels for bearings have their own marking, according to their purpose they form a special group structural steels, although in composition and properties they are close to tool steels. The term "ball bearing" defines their narrow scope - rolling bearings (not only ball bearings, but also roller and needle bearings). For its marking, the abbreviation "SHH" was proposed - ball bearing chromium, followed by a number tenths of a percent medium concentration chrome. Of the previously well-known brands SHKH6, SHKH9 and SHKH15, the SHKH15 brand remained in use. The difference between ball bearing steel and similar tool steel lies in more stringent requirements for the amount of non-metallic inclusions and uniform distribution of carbides in the microstructure.

The improvement of ShKh15 steel by introducing additional alloying additives (silicon and manganese) into it was reflected in the marking in a peculiar way - by spreading to specific a system of later rules for the designation of alloying elements in the composition of alloyed steels: SHKH15SG, SHKH20SG.

High speed steels

High-speed steels are specifically marked with the initial letter of the Russian alphabet "R", corresponding to the first sound in English word rapid - fast, quick. This is followed by an integer percentage of tungsten. As already mentioned, the most common brand of high speed steel used to be P18.

Due to the scarcity and high cost of tungsten, there was a transition to tungsten-molybdenum steel R6M5 without nitrogen and R6AM5 with nitrogen. Similar to bearing steels, there has been a merger (a kind of "hybridization") of the two marking systems. The development and development of new high-speed steels with cobalt and vanadium enriched the arsenal of "hybrid" grades: R6AM5F3, R6M4K8, 11R3AM3F2 - and also led to the emergence of generally tungsten-free high-speed steels, which are marked in a specific system (R0M5F1, R0M2F3), and in a completely new way - 9X6M3F3AGST-Sh, 9X4M3F2AGST-Sh.

Cast iron classification

Cast irons are called alloys of iron with carbon, having in their composition more than 2.14 wt.% C.

Cast irons are smelted for conversion into steel (conversion), to obtain ferroalloys that play the role of alloying additives, and also as high-tech alloys for castings (casting).

Carbon can be in cast iron in the form of two high-carbon phases - cementite (Fe 3 C) and graphite, and sometimes both in the form of cementite and graphite. Cast iron, in which only cementite is present, gives a light, shiny fracture and is therefore called white. The presence of graphite gives the cast iron fracture a gray color. However, not every cast iron with graphite belongs to the class of so-called gray cast irons. Between white and gray cast irons lies the class half-hearted cast irons.

half-hearted cast irons are called cast irons, in the structure of which, despite graphitization, ledeburite cementite is at least partially preserved, which means that ledeburite itself is present - a eutectic structural component having a specific form.

TO gray include cast irons in which ledeburite cementite has completely disintegrated, and the latter has disappeared from the structure. Gray cast iron consists of graphite inclusions And metal base. This metal base is pearlitic (eutectoid), ferritic-pearlitic (hypo-eutectoid) or ferritic (low carbon) steel. The specified sequence of types of the metal base of gray cast irons corresponds to an increasing degree of decomposition of cementite, which is part of perlite.

Anti-friction cast irons

Brand examples: ASF-1, ASF-2, ASF-3.

Special alloyed heat resistant, corrosion resistant And heat resistant cast irons:

EXAMPLES OF SPECIAL GRAY IRON GRADES

Classification and labeling

sintered hard alloys

Metal-ceramic hard alloys are alloys made by powder metallurgy (cermet) and consisting of carbides of refractory metals: WC, TiC, TaC, connected by a plastic metal binder, most often with cobalt.

At present, three groups of hard alloys are produced in Russia: tungsten, titanium-tungsten and titanium-tantalum-tungsten, – containing as a binder cobalt.

Due to the high cost of tungsten, hard alloys have been developed that do not contain tungsten carbide at all. As a solid phase, they contain only titanium carbide or titanium carbonitride– Ti(NC). The role of the plastic ligament is performed by nickel-molybdenum matrix. The classification of hard alloys is represented by a block diagram.

In accordance with the five classes of cermet hard alloys, the existing marking rules form five marking groups.

Tungsten ( sometimes called tungsten-cobalt) hard alloys

Examples: VK3, VK6, VK8, VK10.

Titanium tungsten ( sometimes called titanium-tungsten-cobalt) hard alloys

Examples: T30K4, T15K6, T5K10, T5K12.

Titanium tantalum tungsten ( sometimes called titanium-tantalum-tungsten-cobalt) hard alloys

Examples: TT7K12, TT8K6, TT10K8, TT20K9.

Sometimes, at the end of the brand, letters or letter combinations are added through a hyphen, characterizing the dispersion of carbide particles in the powder:

CLASSIFICATION OF HARD CERAMIC ALLOYS

Foreign analogues some domestic grades of alloy steels are given in table 1.1.

Table 1.1.

Foreign analogues of a number of domestic grades of alloyed steels

Russia, GOST	Germany, DIN*	USA, ASTM*	Japan, LS *
15X	15Cr3		SCr415
40X	41Cr4		SCg440
30XM	25CrMo4		SCM430, SCM2
12HG3A	14NiCr10**	–	SNC815
20HGNM	21NiCrMo2		SNCM220
08X13	X7Cr13 **	410S	SUS410S
20X13	Х20Сг13		SUS420J1
12X17	X8Cr17	430 (51430 ***)	SUS430
12X18H9	X12CrNi8 9		SUS302
08X18H10T	Х10CrNiTi18 9	.321	SUS321
10Х13СУ	X7CrA133 **	405 ** (51405) ***	SUS405**
20Х25Н20С2	Х15CrNiSi25 20	30314,314	SCS18, SUH310 **

* DIN (Deutsche Industrienorm), ASTM (American Societi for Testing Materials), JIS (Japanese industrial Standard).

** Steel similar in composition; *** SAE standard

Characteristics of classification features

And steel classification

The modern classification features of steels include the following:

- quality;

- chemical composition;

- appointment;

- metallurgical features of production;

- microstructure;

- traditional way of hardening;

- the traditional way of obtaining blanks or parts;

- strength.

Let's briefly characterize each of them.

Steel quality is determined primarily by the content of harmful impurities - sulfur and phosphorus - and is characterized by 4 categories (see table. 1.2).

By chemical composition steels are conditionally divided into carbon (non-alloyed) steels and alloyed ones.

carbon steels do not contain specially introduced alloying elements. The elements contained in carbon steels, except for carbon, are among the so-called permanent impurities. Their concentration should be within the limits determined by the relevant state standards(GOSTs). Table 1.3. average concentration limits for some elements are given, allowing these elements to be classified as impurities rather than alloying elements. Specific limits for the content of impurities in carbon steels are given by GOSTs.

Table 1.3.

LIMITING CONCENTRATIONS OF SOME ELEMENTS, ALLOWING THEM TO BE CONSIDERED PERMANENT IMPURITIES

CARBON STEEL

alloying elements, sometimes called alloying additives or additives, are specially introduced into steel to obtain the required structure and properties.

Alloy steels are subdivided according to the total concentration of alloying elements, except for carbon, into low-alloyed(up to 2.5 wt.%), doped(from 2.5 to 10 wt.%) and highly alloyed(more than 10 wt.%) when the content in the latter of iron is not less than 45 wt.%. Usually, the introduced alloying element gives the alloy steel the corresponding name: "chrome"- doped with chromium, "silicon" - with silicon, "chromium-silicon" - with chromium and silicon at the same time, etc.

In addition, iron-based alloys are also distinguished, when the iron content of the material is less than 45%, but it is more than any other alloying element.

According to the purpose of steel subdivided into structural and instrumental.

Structural steels used for the manufacture of various machine parts, mechanisms and structures in mechanical engineering, construction and instrument making are considered. They must have the necessary strength and toughness, as well as, if required, a set of special properties (corrosion resistance, paramagnetism, etc.). As a rule, structural steels are low-( or few-) And medium carbon. Hardness is not a decisive mechanical characteristic for them.

instrumental called steels used for processing materials by cutting or pressure, as well as for the manufacture of measuring tools. They must have high hardness, wear resistance, strength and a number of other specific properties, for example, heat resistance. A necessary condition for obtaining high hardness is an increased carbon content, so tool steels, with rare exceptions, are always high carbon.

Within each of the groups there is a more detailed division according to purpose. Structural steels are divided into construction, engineering And special application steels(with special properties - heat-resistant, heat-resistant, corrosion-resistant, non-magnetic).

Tool steels are divided into cutting tool steels, die steels And steel for measuring instruments.

A common operational property of tool steels is high hardness, which ensures the resistance of the tool to deformation and abrasion of its surface. At the same time, a specific requirement is imposed on steels for cutting tools - to maintain high hardness at elevated temperatures (up to 500 ... 600ºС), which develop in the cutting edge at high cutting speeds. The indicated ability of steel is called its heat resistance (or red hardness). According to the specified criterion, steels for cutting tools are divided into non-heat-resistant, semi-heat-resistant, heat-resistant And increased heat resistance. The last two groups are known in the art under the name fast cutting steels.

From die steels, in addition to high hardness, high toughness is required, since the die tool works under shock loading conditions. In addition, the tool for hot stamping, in contact with heated metal blanks, can heat up during prolonged work. Therefore, steels for hot stamping must also be heat resistant.

Measuring tool steels, in addition to high wear resistance, ensuring dimensional accuracy over a long service life, must guarantee tool dimensional stability regardless of operating temperature conditions. In other words, they should have a very small thermal expansion coefficient.

Classification of inorganic substances with examples of compounds

Let us now analyze the classification scheme presented above in more detail.

As we can see, first of all, all inorganic substances are divided into simple And complex:

simple substances substances that are formed by atoms of only one chemical element are called. For example, simple substances are hydrogen H 2 , oxygen O 2 , iron Fe, carbon C, etc.

Among simple substances, there are metals, nonmetals And noble gases:

Metals are formed by chemical elements located below the boron-astat diagonal, as well as by all elements that are in side groups.

noble gases formed by chemical elements of group VIIIA.

non-metals formed, respectively, by chemical elements located above the boron-astat diagonal, with the exception of all elements of secondary subgroups and noble gases located in group VIIIA:

The names of simple substances most often coincide with the names chemical elements, the atoms of which they are formed. However, for many chemical elements, the phenomenon of allotropy is widespread. Allotropy is the phenomenon when one chemical element is able to form several simple substances. For example, in the case of the chemical element oxygen, the existence of molecular compounds with the formulas O 2 and O 3 is possible. The first substance is usually called oxygen in the same way as the chemical element whose atoms it is formed, and the second substance (O 3) is usually called ozone. A simple substance carbon can mean any of its allotropic modifications, for example, diamond, graphite or fullerenes. The simple substance phosphorus can be understood as its allotropic modifications, such as white phosphorus, red phosphorus, black phosphorus.

Complex Substances

complex substances Substances made up of atoms of two or more elements are called.

So, for example, complex substances are ammonia NH 3, sulfuric acid H 2 SO 4, slaked lime Ca (OH) 2 and countless others.

Among complex inorganic substances, 5 main classes are distinguished, namely oxides, bases, amphoteric hydroxides, acids and salts:

oxides - complex substances formed by two chemical elements, one of which is oxygen in the oxidation state -2.

General formula oxides can be written as E x O y , where E is the symbol of some chemical element.

Nomenclature of oxides

The name of the oxide of a chemical element is based on the principle:

For example:

Fe 2 O 3 - iron oxide (III); CuO, copper(II) oxide; N 2 O 5 - nitric oxide (V)

Often you can find information that the valency of the element is indicated in brackets, but this is not the case. So, for example, the oxidation state of nitrogen N 2 O 5 is +5, and the valence, oddly enough, is four.

If a chemical element has a single positive oxidation state in compounds, then the oxidation state is not indicated. For example:

Na 2 O - sodium oxide; H 2 O - hydrogen oxide; ZnO is zinc oxide.

Classification of oxides

Oxides, according to their ability to form salts when interacting with acids or bases, are divided, respectively, into salt-forming And non-salt-forming.

There are few non-salt-forming oxides; they are all formed by non-metals in the +1 and +2 oxidation states. The list of non-salt-forming oxides should be remembered: CO, SiO, N 2 O, NO.

Salt-forming oxides, in turn, are divided into main, acidic And amphoteric.

Basic oxides called such oxides, which, when interacting with acids (or acid oxides), form salts. The main oxides include metal oxides in the oxidation state +1 and +2, with the exception of oxides of BeO, ZnO, SnO, PbO.

Acid oxides called such oxides, which, when interacting with bases (or basic oxides), form salts. Acid oxides are practically all oxides of non-metals, with the exception of non-salt-forming CO, NO, N 2 O, SiO, as well as all metal oxides in high oxidation states (+5, +6 and +7).

amphoteric oxides called oxides, which can react with both acids and bases, and as a result of these reactions form salts. Such oxides exhibit a dual acid-base nature, that is, they can exhibit the properties of both acidic and basic oxides. Amphoteric oxides include metal oxides in oxidation states +3, +4, and, as exceptions, oxides of BeO, ZnO, SnO, PbO.

Some metals can form all three types of salt-forming oxides. For example, chromium forms basic oxide CrO, amphoteric oxide Cr 2 O 3 and acid oxide CrO 3 .

As can be seen, the acid-base properties of metal oxides directly depend on the degree of oxidation of the metal in the oxide: the higher the degree of oxidation, the more pronounced the acid properties.

Foundations

Foundations - compounds with a formula of the form Me (OH) x, where x most often equal to 1 or 2.

Exceptions: Be (OH) 2, Zn (OH) 2, Sn (OH) 2 and Pb (OH) 2 do not belong to the bases, despite the oxidation state of the metal +2. These compounds are amphoteric hydroxides, which will be discussed in more detail in this chapter.

Base classification

Bases are classified according to the number of hydroxo groups in one structural unit.

Bases with one hydroxo group, i.e. type MeOH, called single acid bases with two hydroxo groups, i.e. type Me(OH) 2 , respectively, diacid etc.

Also, the bases are divided into soluble (alkali) and insoluble.

Alkalis include exclusively hydroxides of alkali and alkaline earth metals, as well as thallium hydroxide TlOH.

Base nomenclature

The name of the foundation is built according to the following principle:

For example:

Fe (OH) 2 - iron (II) hydroxide,

Cu (OH) 2 - copper (II) hydroxide.

In cases where the metal in complex substances has a constant oxidation state, it is not required to indicate it. For example:

NaOH - sodium hydroxide,

Ca (OH) 2 - calcium hydroxide, etc.

acids

acids - complex substances, the molecules of which contain hydrogen atoms that can be replaced by a metal.

The general formula of acids can be written as H x A, where H are hydrogen atoms that can be replaced by a metal, and A is an acid residue.

For example, acids include compounds such as H 2 SO 4 , HCl, HNO 3 , HNO 2 , etc.

Acid classification

According to the number of hydrogen atoms that can be replaced by a metal, acids are divided into:

- about monobasic acids: HF, HCl, HBr, HI, HNO 3 ;

- d acetic acids: H 2 SO 4 , H 2 SO 3 , H 2 CO 3 ;

- T rebasic acids: H 3 PO 4 , H 3 BO 3 .

It should be noted that the number of hydrogen atoms in the case of organic acids most often does not reflect their basicity. For example, acetic acid with the formula CH 3 COOH, despite the presence of 4 hydrogen atoms in the molecule, is not four-, but monobasic. The basicity of organic acids is determined by the amount carboxyl groups(-COOH) in the molecule.

Also, according to the presence of oxygen in acid molecules, they are divided into anoxic (HF, HCl, HBr, etc.) and oxygen-containing (H 2 SO 4, HNO 3, H 3 PO 4, etc.). Oxygenated acids are also called oxo acids.

You can read more about the classification of acids.

Nomenclature of acids and acid residues

The following list of names and formulas of acids and acid residues should be learned.

In some cases, a number of the following rules can make memorization easier.

As can be seen from the table above, the construction of the systematic names of anoxic acids is as follows:

For example:

HF, hydrofluoric acid;

HCl, hydrochloric acid;

H 2 S - hydrosulfide acid.

The names of the acid residues of oxygen-free acids are built according to the principle:

For example, Cl - - chloride, Br - - bromide.

The names of oxygen-containing acids are obtained by adding various suffixes and endings to the name of the acid-forming element. For example, if the acid-forming element in an oxygen-containing acid has the highest degree oxidation, then the name of such an acid is constructed as follows:

For example, sulfuric acid H 2 S +6 O 4, chromic acid H 2 Cr +6 O 4.

All oxygen-containing acids can also be classified as acidic hydroxides, since hydroxo groups (OH) are found in their molecules. For example, this can be seen from the following graphical formulas of some oxygen-containing acids:

Thus, sulfuric acid can otherwise be called sulfur (VI) hydroxide, nitric acid - nitrogen (V) hydroxide, phosphoric acid - phosphorus (V) hydroxide, etc. The number in brackets characterizes the degree of oxidation of the acid-forming element. Such a variant of the names of oxygen-containing acids may seem extremely unusual to many, but occasionally such names can be found in real KIMs of the Unified State Examination in chemistry in assignments for the classification of inorganic substances.

Amphoteric hydroxides

Amphoteric hydroxides - metal hydroxides exhibiting a dual nature, i.e. capable of exhibiting both the properties of acids and the properties of bases.

Amphoteric are metal hydroxides in oxidation states +3 and +4 (as well as oxides).

Also, compounds Be (OH) 2, Zn (OH) 2, Sn (OH) 2 and Pb (OH) 2 are included as exceptions to amphoteric hydroxides, despite the degree of oxidation of the metal in them +2.

For amphoteric hydroxides of tri- and tetravalent metals, the existence of ortho- and meta-forms is possible, differing from each other by one water molecule. For example, aluminum (III) hydroxide can exist in the ortho form of Al(OH) 3 or the meta form of AlO(OH) (metahydroxide).

Since, as already mentioned, amphoteric hydroxides exhibit both the properties of acids and the properties of bases, their formula and name can also be written differently: either as a base or as an acid. For example:

salt

salt - these are complex substances, which include metal cations and anions of acid residues.

So, for example, salts include compounds such as KCl, Ca(NO 3) 2, NaHCO 3, etc.

The above definition describes the composition of most salts, however, there are salts that do not fall under it. For example, instead of metal cations, the salt may contain ammonium cations or its organic derivatives. Those. salts include compounds such as, for example, (NH 4) 2 SO 4 (ammonium sulfate), + Cl - (methylammonium chloride), etc.

Also contrary to the definition of salts above is the class of so-called complex salts, which will be discussed at the end of this topic.

Salt classification

On the other hand, salts can be considered as products of substitution of hydrogen cations H + in an acid for other cations, or as products of substitution of hydroxide ions in bases (or amphoteric hydroxides) for other anions.

With complete substitution, the so-called medium or normal salt. For example, with the complete replacement of hydrogen cations in sulfuric acid with sodium cations, an average (normal) salt Na 2 SO 4 is formed, and with the complete replacement of hydroxide ions in the Ca (OH) 2 base with acid residues, nitrate ions form an average (normal) salt Ca(NO3)2.

Salts obtained by incomplete replacement of hydrogen cations in a dibasic (or more) acid with metal cations are called acidic. So, with incomplete replacement of hydrogen cations in sulfuric acid by sodium cations, an acid salt NaHSO 4 is formed.

Salts that are formed by incomplete substitution of hydroxide ions in two-acid (or more) bases are called basic about salts. For example, with incomplete replacement of hydroxide ions in the Ca (OH) 2 base with nitrate ions, a basic about clear salt Ca(OH)NO 3 .

Salts consisting of cations of two different metals and anions of acid residues of only one acid are called double salts. So, for example, double salts are KNaCO 3 , KMgCl 3 , etc.

If the salt is formed by one type of cation and two types of acid residues, such salts are called mixed. For example, mixed salts are the compounds Ca(OCl)Cl, CuBrCl, etc.

There are salts that do not fall under the definition of salts as products of substitution of hydrogen cations in acids for metal cations or products of substitution of hydroxide ions in bases for anions of acid residues. These are complex salts. So, for example, complex salts are sodium tetrahydroxozincate and tetrahydroxoaluminate with the formulas Na 2 and Na, respectively. Recognize complex salts, among others, most often by the presence of square brackets in the formula. However, it must be understood that in order for a substance to be classified as a salt, its composition must include any cations, except for (or instead of) H +, and from the anions there must be any anions in addition to (or instead of) OH -. For example, the compound H 2 does not belong to the class of complex salts, since only hydrogen cations H + are present in solution during its dissociation from cations. According to the type of dissociation, this substance should rather be classified as an oxygen-free complex acid. Similarly, the OH compound does not belong to the salts, because this compound consists of cations + and hydroxide ions OH -, i.e. it should be considered a complex basis.

Salt nomenclature

Nomenclature of medium and acid salts

The name of medium and acid salts is based on the principle:

If the degree of oxidation of the metal in complex substances is constant, then it is not indicated.

The names of the acid residues were given above when considering the nomenclature of acids.

For example,

Na 2 SO 4 - sodium sulfate;

NaHSO 4 - sodium hydrosulfate;

CaCO 3 - calcium carbonate;

Ca (HCO 3) 2 - calcium bicarbonate, etc.

Nomenclature of basic salts

The names of the main salts are built according to the principle:

For example:

(CuOH) 2 CO 3 - copper (II) hydroxocarbonate;

Fe (OH) 2 NO 3 - iron (III) dihydroxonitrate.

Nomenclature of complex salts

The nomenclature of complex compounds is much more complicated, and you don’t need to know much from the nomenclature of complex salts to pass the exam.

One should be able to name complex salts obtained by the interaction of alkali solutions with amphoteric hydroxides. For example:

*The same colors in the formula and the name indicate the corresponding elements of the formula and the name.

Trivial names of inorganic substances

Trivial names are understood as the names of substances that are not related, or weakly related to their composition and structure. Trivial names are due, as a rule, either to historical reasons, or to physical or chemical properties connection data.

List of trivial names of inorganic substances that you need to know:

Na 3	cryolite
SiO2	quartz, silica
FeS 2	pyrite, iron pyrite
CaSO 4 ∙2H 2 O	gypsum
CaC2	calcium carbide
Al 4 C 3	aluminum carbide
KOH	caustic potash
NaOH	caustic soda, caustic soda
H2O2	hydrogen peroxide
CuSO 4 ∙5H 2 O	blue vitriol
NH4Cl	ammonia
CaCO3	chalk, marble, limestone
N2O	laughing gas
NO 2	brown gas
NaHCO3	food (drinking) soda
Fe 3 O 4	iron oxide
NH 3 ∙H 2 O (NH 4 OH)	ammonia
CO	carbon monoxide
CO2	carbon dioxide
SiC	carborundum (silicon carbide)
PH 3	phosphine
NH3	ammonia
KClO 3	berthollet salt (potassium chlorate)
(CuOH) 2 CO 3	malachite
CaO	quicklime
Ca(OH)2	slaked lime
transparent aqueous solution of Ca(OH) 2	lime water
a suspension of solid Ca (OH) 2 in its aqueous solution	milk of lime
K2CO3	potash
Na2CO3	soda ash
Na 2 CO 3 ∙10H 2 O	crystal soda
MgO	magnesia

CHEMICAL-TECHNOLOGICAL PROCESS AND ITS CONTENT

The chemical-technological process is a set of operations that make it possible to obtain the target product from the feedstock. All these operations are part of three main stages, characteristic of almost every chemical-technological process.

At the first stage, the operations necessary to prepare the initial reagents for a chemical reaction are carried out. The reagents are transferred, in particular, to the most reactive state. For example, it is known that the rate of chemical reactions strongly depends on temperature, so often the reagents are heated before the reaction. Gaseous raw materials are subjected to compression to a certain pressure to increase the efficiency of the process and reduce the size of the equipment. To eliminate side effects and obtain a high quality product, the feedstock is subjected to purification from impurities using methods based on the difference in physical properties (solubility in various solvents, density, condensation and crystallization temperatures, etc.). In the purification of raw materials and reaction mixtures, the phenomena of heat and mass transfer, hydromechanical processes are widely used. Can also be used chemical methods purifications based on chemical reactions, as a result of which unwanted impurities are converted into easily separable substances.

Appropriately prepared reagents in the next stage are subjected to chemical interaction, which may consist of several stages. In the intervals between these stages, it is sometimes necessary to reuse heat and mass transfer and other physical processes. For example, in the production of sulfuric acid, sulfur dioxide is partially oxidized to trioxide, then the reaction mixture is cooled, sulfur trioxide is removed from it by absorption, and again directed to oxidation.

As a result of chemical reactions, a mixture of products (target, by-products, by-products) and unreacted reagents is obtained. The final operations of the last stage are associated with the separation of this mixture, for which hydromechanical, heat and mass transfer processes are again used, for example: filtration, centrifugation, rectification, absorption, extraction, etc. The reaction products are sent to the finished product warehouse or for further processing; unreacted raw materials are reused in the process, organizing its recycling.

At all stages, and especially at the final ones, the recovery of secondary material and energy resources is also carried out. The streams of gaseous and liquid substances entering the environment are subjected to purification and neutralization from hazardous impurities. Solid waste is either sent for further processing or placed for storage in safe environment conditions.

Thus, the chemical-technological process as a whole is a complex system consisting of single interconnected processes (elements) and interacting with the environment.

The elements of the chemical-technological system are the above processes of heat and mass transfer, hydromechanical, chemical, etc. They are considered as single processes of chemical technology.

An important subsystem of a complex chemical-technological process is a chemical process.

chemical process is one or more chemical reactions accompanied by the phenomena of heat, mass and momentum transfer, affecting both each other and the course of a chemical reaction.

Analysis of individual processes, their mutual influence allows us to develop a technological regime.

A technological regime is a set of technological parameters (temperature, pressure, concentrations of reagents, etc.) that determine the operating conditions of an apparatus or a system of apparatuses (technological scheme).

Optimal process conditions are a combination of the main parameters (temperature, pressure, composition of the initial reaction mixture, etc.), which makes it possible to obtain the highest product yield at a high speed or to ensure the lowest cost, subject to the conditions for the rational use of raw materials and energy and minimizing possible damage to the environment. environment.

Single processes take place in various apparatuses - chemical reactors, absorption and distillation columns, heat exchangers, etc. Separate apparatuses are connected in a process flow diagram.

Technological scheme is a rationally constructed system of single devices connected by various types of connections (direct, reverse, serial, parallel), which allows obtaining a given product of a given quality from natural raw materials or semi-finished products.

Technological schemes are open and closed, may contain bypass (bypass) flows and recycles, allowing to increase the efficiency of the chemical-technological system as a whole.

The development and construction of a rational technological scheme is an important task of chemical technology.

Classification of chemical reactions underlying industrial chemical-technological processes

IN modern chemistry a large number of different chemical reactions are known. Many of them are carried out in industrial chemical reactors and, therefore, become the object of study in chemical engineering.

To facilitate the study of phenomena close in nature, it is customary in science to classify them according to common features. Depending on what signs are taken as a basis, there are several types of classification of chemical reactions.

An important type of classification is the classification by mechanism for the reaction. There are simple (single-stage) and complex (multi-stage) reactions, in particular, parallel, sequential and series-parallel.

Simple reactions are called, for the implementation of which it is required to overcome only one energy barrier (one stage).

Complex reactions include several parallel or sequential steps (simple reactions).

Real one-step reactions are extremely rare. However, some complex reactions passing through a series of intermediate stages can conveniently be considered formally simple. This is possible in cases where intermediate reaction products are not detected under the conditions of the problem under consideration.

Reaction classification by molecularity takes into account how many molecules are involved in the elementary act of the reaction; distinguish between mono-, bi- and trimolecular reactions.

The form of the kinetic equation (the dependence of the reaction rate on the concentrations of reagents) allows us to classify in order of reaction. The reaction order is the sum of the exponents of the concentrations of the reactants in the kinetic equation. There are reactions of the first, second, third, fractional orders.

Chemical reactions are also by thermal effect. When exothermic reactions occur, accompanied by the release of heat ( Q> 0), the enthalpy of the reaction system decreases ( ∆H < 0); при протекании эндотермических реакций, сопровождающихся поглощением теплоты (Q< 0), the enthalpy of the reaction system increases ( ∆H> 0).

For the choice of the design of a chemical reactor and methods for controlling the conduct of the process, it is essential phase composition reaction system.

Depending on how many (one or more) phases form the initial reagents and reaction products, chemical reactions are divided into homophasic and heterophasic.

Homophasic reactions are those in which the reactants, stable intermediates, and reaction products are all within the same phase.

Reactions are called heterophasic in which the starting reagents, stable intermediates, and reaction products form more than one phase.

Depending on the leak zones reactions are divided into homogeneous and heterogeneous reactions.

The concepts of "homogeneous" and "heterogeneous" reactions do not coincide with the concepts of "homophasic" and "heterophasic" processes. The homogeneity and heterogeneity of a reaction reflects, to a certain extent, its mechanism: whether the reaction proceeds in the bulk of a single phase or at the phase interface. The homophasic and heterophasic nature of the process only makes it possible to judge the phase composition of the reaction participants.

In the case of homogeneous reactions, the reactants and products are in the same phase (liquid or gaseous) and the reaction proceeds in the volume of this phase. For example, the oxidation of nitric oxide with atmospheric oxygen in the production of nitric acid is a gas-phase reaction, while esterification reactions (obtaining esters from organic acids and alcohols) are liquid-phase.

When heterogeneous reactions occur, at least one of the reactants or products is in a phase state that differs from the phase state of the other participants, and the phase interface must be taken into account when analyzing it. For example, the neutralization of an acid with an alkali is a homophasic homogeneous process. The catalytic synthesis of ammonia is a homophasic heterogeneous process. The oxidation of hydrocarbons in the liquid phase with gaseous oxygen is a heterophasic process, but the ongoing chemical reaction is homogeneous. The slaking of lime CaO + H 2 O Ca (OH) 2, in which all three participants in the reaction form separate phases, and the reaction proceeds at the interface between water and calcium oxide, is a heterophase heterogeneous process.

Depending on whether or not special substances, catalysts, are used to change the reaction rate, they are distinguished catalytic And non-catalytic reactions and, accordingly, chemical-technological processes. The vast majority of chemical reactions on which industrial chemical-technological processes are based are catalytic reactions.

Chemical reactions should be distinguished from nuclear reactions. As a result of chemical reactions, the total number of atoms of each chemical element and its isotopic composition do not change. Another thing nuclear reactions- the processes of transformation of atomic nuclei as a result of their interaction with other nuclei or elementary particles, for example, the conversion of aluminum to magnesium:

27 13 Al + 1 1 H \u003d 24 12 Mg + 4 2 He

The classification of chemical reactions is multifaceted, that is, it can be based on various signs. But under any of these signs, reactions both between inorganic and between organic substances can be attributed.

Consider the classification of chemical reactions according to various criteria.

I. According to the number and composition of the reactants

Reactions that take place without changing the composition of substances.

In inorganic chemistry, such reactions include the processes of obtaining allotropic modifications of one chemical element, for example:

C (graphite) ↔ C (diamond)
S (rhombic) ↔ S (monoclinic)
R (white) ↔ R (red)
Sn (white tin) ↔ Sn (grey tin)
3O 2 (oxygen) ↔ 2O 3 (ozone)

In organic chemistry, this type of reactions can include isomerization reactions that occur without changing not only the qualitative, but also the quantitative composition of the molecules of substances, for example:

1. Isomerization of alkanes.

The reaction of isomerization of alkanes is of great practical importance, since hydrocarbons of the isostructure have a lower ability to detonate.

2. Isomerization of alkenes.

3. Isomerization of alkynes (reaction of A. E. Favorsky).

CH 3 - CH 2 - C \u003d - CH ↔ CH 3 - C \u003d - C- CH 3

ethylacetylene dimethylacetylene

4. Isomerization of haloalkanes (A. E. Favorsky, 1907).

5. Isomerization of ammonium cyanite upon heating.

For the first time, urea was synthesized by F. Wehler in 1828 by isomerization of ammonium cyanate when heated.

Reactions that go with a change in the composition of a substance

There are four types of such reactions: compounds, decompositions, substitutions and exchanges.

1. Connection reactions are such reactions in which one complex substance is formed from two or more substances

In inorganic chemistry, the whole variety of compound reactions can be considered, for example, using the example of reactions for obtaining sulfuric acid from sulfur:

1. Obtaining sulfur oxide (IV):

S + O 2 \u003d SO - one complex substance is formed from two simple substances.

2. Obtaining sulfur oxide (VI):

SO 2 + 0 2 → 2SO 3 - one complex substance is formed from a simple and complex substance.

3. Obtaining sulfuric acid:

SO 3 + H 2 O \u003d H 2 SO 4 - one complex is formed from two complex substances.

An example of a compound reaction in which one complex substance is formed from more than two starting materials is the final stage in the production of nitric acid:

4NO 2 + O 2 + 2H 2 O \u003d 4HNO 3

In organic chemistry, compound reactions are commonly referred to as "addition reactions". The whole variety of such reactions can be considered on the example of a block of reactions characterizing the properties of unsaturated substances, for example, ethylene:

1. Hydrogenation reaction - hydrogen addition:

CH 2 \u003d CH 2 + H 2 → H 3 -CH 3

ethene → ethane

2. Hydration reaction - addition of water.

3. Polymerization reaction.

2. Decomposition reactions are such reactions in which several new substances are formed from one complex substance.

In inorganic chemistry, the whole variety of such reactions can be considered in the block of reactions for obtaining oxygen by laboratory methods:

1. Decomposition of mercury (II) oxide - two simple ones are formed from one complex substance.

2. Decomposition of potassium nitrate - from one complex substance, one simple and one complex are formed.

3. Decomposition of potassium permanganate - from one complex substance, two complex and one simple are formed, that is, three new substances.

In organic chemistry, decomposition reactions can be considered on the block of reactions for the production of ethylene in the laboratory and in industry:

1. The reaction of dehydration (water splitting) of ethanol:

C 2 H 5 OH → CH 2 \u003d CH 2 + H 2 O

2. Dehydrogenation reaction (hydrogen splitting) of ethane:

CH 3 -CH 3 → CH 2 \u003d CH 2 + H 2

or CH 3 -CH 3 → 2C + ZH 2

3. Cracking reaction (splitting) of propane:

CH 3 -CH 2 -CH 3 → CH 2 \u003d CH 2 + CH 4

3. Substitution reactions are such reactions as a result of which the atoms of a simple substance replace the atoms of an element in a complex substance.

In inorganic chemistry, an example of such processes is a block of reactions that characterize the properties of, for example, metals:

1. Interaction of alkali or alkaline earth metals with water:

2Na + 2H 2 O \u003d 2NaOH + H 2

2. Interaction of metals with acids in solution:

Zn + 2HCl = ZnCl 2 + H 2

3. Interaction of metals with salts in solution:

Fe + CuSO 4 = FeSO 4 + Cu

4. Metalthermy:

2Al + Cr 2 O 3 → Al 2 O 3 + 2Cr

The subject of study of organic chemistry is not simple substances, but only compounds. Therefore, as an example of a substitution reaction, we give the most characteristic property of saturated compounds, in particular methane, the ability of its hydrogen atoms to be replaced by halogen atoms. Another example is the bromination of an aromatic compound (benzene, toluene, aniline).

C 6 H 6 + Br 2 → C 6 H 5 Br + HBr

benzene → bromobenzene

Let us pay attention to the peculiarity of the substitution reaction in organic substances: as a result of such reactions, not a simple and complex substance is formed, as in inorganic chemistry, but two complex substances.

In organic chemistry, substitution reactions also include some reactions between two complex substances, for example, the nitration of benzene. It is formally an exchange reaction. The fact that this is a substitution reaction becomes clear only when considering its mechanism.

4. Exchange reactions are such reactions in which two complex substances exchange their constituent parts

These reactions characterize the properties of electrolytes and proceed in solutions according to the Berthollet rule, that is, only if a precipitate, gas, or a low-dissociating substance (for example, H 2 O) is formed as a result.

In inorganic chemistry, this can be a block of reactions characterizing, for example, the properties of alkalis:

1. Neutralization reaction that goes with the formation of salt and water.

2. The reaction between alkali and salt, which goes with the formation of gas.

3. The reaction between alkali and salt, which goes with the formation of a precipitate:

СuSO 4 + 2KOH \u003d Cu (OH) 2 + K 2 SO 4

or in ionic form:

Cu 2+ + 2OH - \u003d Cu (OH) 2

In organic chemistry, one can consider a block of reactions characterizing, for example, the properties of acetic acid:

1. The reaction proceeding with the formation of a weak electrolyte - H 2 O:

CH 3 COOH + NaOH → Na (CH3COO) + H 2 O

2. The reaction that goes with the formation of gas:

2CH 3 COOH + CaCO 3 → 2CH 3 COO + Ca 2+ + CO 2 + H 2 O

3. The reaction proceeding with the formation of a precipitate:

2CH 3 COOH + K 2 SO 3 → 2K (CH 3 COO) + H 2 SO 3

2CH 3 COOH + SiO → 2CH 3 COO + H 2 SiO 3

II. By changing the oxidation states of chemical elements that form substances

On this basis, the following reactions are distinguished:

1. Reactions that occur with a change in the oxidation states of elements, or redox reactions.

These include many reactions, including all substitution reactions, as well as those reactions of combination and decomposition in which at least one simple substance participates, for example:

1. Mg 0 + H + 2 SO 4 \u003d Mg + 2 SO 4 + H 2

2. 2Mg 0 + O 0 2 = Mg +2 O -2

Complex redox reactions are compiled using the electron balance method.

2KMn +7 O 4 + 16HCl - \u003d 2KCl - + 2Mn +2 Cl - 2 + 5Cl 0 2 + 8H 2 O

In organic chemistry, the properties of aldehydes can serve as a striking example of redox reactions.

1. They are reduced to the corresponding alcohols:

Aldecides are oxidized to the corresponding acids:

2. Reactions that take place without changing the oxidation states of chemical elements.

These include, for example, all ion exchange reactions, as well as many compound reactions, many decomposition reactions, esterification reactions:

HCOOH + CHgOH = HSOCH 3 + H 2 O

III. By thermal effect

According to the thermal effect, the reactions are divided into exothermic and endothermic.

1. Exothermic reactions proceed with the release of energy.

These include almost all compound reactions. A rare exception is the endothermic reactions of the synthesis of nitric oxide (II) from nitrogen and oxygen and the reaction of gaseous hydrogen with solid iodine.

Exothermic reactions that proceed with the release of light are referred to as combustion reactions. The hydrogenation of ethylene is an example of an exothermic reaction. It runs at room temperature.

2. Endothermic reactions proceed with the absorption of energy.

Obviously, almost all decomposition reactions will apply to them, for example:

1. Calcination of limestone

2. Butane cracking

The amount of energy released or absorbed as a result of the reaction is called the thermal effect of the reaction, and the equation of a chemical reaction indicating this effect is called the thermochemical equation:

H 2 (g) + C 12 (g) \u003d 2HC 1 (g) + 92.3 kJ

N 2 (g) + O 2 (g) \u003d 2NO (g) - 90.4 kJ

IV. According to the state of aggregation of reacting substances (phase composition)

According to the state of aggregation of the reacting substances, there are:

1. Heterogeneous reactions - reactions in which the reactants and reaction products are in different states of aggregation (in different phases).

2. Homogeneous reactions - reactions in which the reactants and reaction products are in the same state of aggregation (in one phase).

V. According to the participation of the catalyst

According to the participation of the catalyst, there are:

1. Non-catalytic reactions that take place without the participation of a catalyst.

2. Catalytic reactions taking place with the participation of a catalyst. Since all biochemical reactions occurring in the cells of living organisms proceed with the participation of special biological catalysts of protein nature - enzymes, they are all catalytic or, more precisely, enzymatic. It should be noted that more than 70% of chemical industries use catalysts.

VI. Towards

By direction there are:

1. Irreversible reactions proceed under given conditions in only one direction. These include all exchange reactions accompanied by the formation of a precipitate, gas or a low-dissociating substance (water) and all combustion reactions.

2. Reversible reactions under these conditions proceed simultaneously in two opposite directions. Most of these reactions are.

In organic chemistry, the sign of reversibility is reflected in the names - antonyms of processes:

Hydrogenation - dehydrogenation,

Hydration - dehydration,

Polymerization - depolymerization.

All esterification reactions are reversible (the opposite process, as you know, is called hydrolysis) and hydrolysis of proteins, esters, carbohydrates, polynucleotides. The reversibility of these processes underlies the most important property of a living organism - metabolism.

VII. According to the mechanism of flow, there are:

1. Radical reactions take place between the radicals and molecules formed during the reaction.

As you already know, in all reactions, old chemical bonds are broken and new chemical bonds are formed. The method of breaking the bond in the molecules of the starting substance determines the mechanism (path) of the reaction. If the substance is formed by a covalent bond, then there can be two ways to break this bond: hemolytic and heterolytic. For example, for the molecules of Cl 2 , CH 4 , etc., a hemolytic rupture of bonds is realized, it will lead to the formation of particles with unpaired electrons, that is, free radicals.

Radicals are most often formed when bonds are broken in which the shared electron pairs are distributed approximately equally between atoms (non-polar covalent bond), but many polar bonds can also be broken in a similar way, in particular when the reaction takes place in the gas phase and under the influence of light , as, for example, in the case of the processes discussed above - the interaction of C 12 and CH 4 - . Radicals are highly reactive, as they tend to complete their electron layer by taking an electron from another atom or molecule. For example, when a chlorine radical collides with a hydrogen molecule, it breaks the shared electron pair that binds the hydrogen atoms and forms a covalent bond with one of the hydrogen atoms. The second hydrogen atom, becoming a radical, forms a common electron pair with the unpaired electron of the chlorine atom from the collapsing Cl 2 molecule, resulting in a chlorine radical that attacks a new hydrogen molecule, etc.

Reactions, which are a chain of successive transformations, are called chain reactions. For the development of the theory of chain reactions, two outstanding chemists - our compatriot N. N. Semenov and the Englishman S. A. Hinshelwood were awarded the Nobel Prize.
The substitution reaction between chlorine and methane proceeds similarly:

Most of the combustion reactions of organic and inorganic substances, the synthesis of water, ammonia, the polymerization of ethylene, vinyl chloride, etc. proceed according to the radical mechanism.

2. Ionic reactions take place between ions already present or formed during the reaction.

Typical ionic reactions are interactions between electrolytes in solution. Ions are formed not only during the dissociation of electrolytes in solutions, but also under the action of electrical discharges, heating or radiation. γ-rays, for example, convert water and methane molecules into molecular ions.

According to another ionic mechanism, reactions of addition of hydrogen halides, hydrogen, halogens to alkenes, oxidation and dehydration of alcohols, replacement of alcohol hydroxyl by halogen occur; reactions characterizing the properties of aldehydes and acids. Ions in this case are formed by heterolytic breaking of covalent polar bonds.

VIII. According to the type of energy

initiating the reaction, there are:

1. Photochemical reactions. They are initiated by light energy. In addition to the above photochemical processes of HCl synthesis or the reaction of methane with chlorine, they include the production of ozone in the troposphere as a secondary atmospheric pollutant. In this case, nitric oxide (IV) acts as the primary one, which forms oxygen radicals under the action of light. These radicals interact with oxygen molecules, resulting in ozone.

The formation of ozone goes on as long as there is enough light, since NO can interact with oxygen molecules to form the same NO 2 . The accumulation of ozone and other secondary air pollutants can lead to photochemical smog.

This type of reaction also includes the most important process that occurs in plant cells - photosynthesis, the name of which speaks for itself.

2. Radiation reactions. They are initiated by high-energy radiation - x-rays, nuclear radiation (γ-rays, a-particles - He 2+, etc.). With the help of radiation reactions, very fast radiopolymerization, radiolysis (radiation decomposition), etc. are carried out.

For example, instead of a two-stage production of phenol from benzene, it can be obtained by the interaction of benzene with water under the action of radiation. In this case, radicals [OH] and [H] are formed from water molecules, with which benzene reacts to form phenol:

C 6 H 6 + 2 [OH] → C 6 H 5 OH + H 2 O

Rubber vulcanization can be carried out without sulfur using radiovulcanization, and the resulting rubber will be no worse than traditional rubber.

3. Electrochemical reactions. They are initiated electricity. In addition to the electrolysis reactions well known to you, we will also indicate the reactions of electrosynthesis, for example, the reactions of the industrial production of inorganic oxidants

4. Thermochemical reactions. They are initiated by thermal energy. These include all endothermic reactions and many exothermic reactions that require an initial supply of heat, that is, the initiation of the process.

The above classification of chemical reactions is reflected in the diagram.

The classification of chemical reactions, like all other classifications, is conditional. Scientists agreed to divide the reactions into certain types according to the signs they identified. But most chemical transformations can be attributed to different types. For example, let's characterize the ammonia synthesis process.

This is a compound reaction, redox, exothermic, reversible, catalytic, heterogeneous (more precisely, heterogeneous catalytic), proceeding with a decrease in pressure in the system. To successfully manage the process, all of the above information must be taken into account. A specific chemical reaction is always multi-qualitative, it is characterized by different features.