Classification of chemical reactions in inorganic and organic chemistry

Chemical reactions, or chemical phenomena, are processes as a result of which others are formed from some substances, differing from them in composition and (or) structure.

In chemical reactions, a change in substances necessarily occurs, in which old bonds are broken and new bonds are formed between atoms.

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

$↙(13)↖(27)(Al)+ ()↙(1)↖(1)(H)=()↙(12)↖(24)(Mg)+()↙(2)↖(4 )(He)$

The classification of chemical reactions is multifaceted, i.e. It can be based on various features. 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.

Classification of chemical reactions according to the number and composition of reactants. Reactions that take place without changing the composition of the substance

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

$С_((graphite))⇄С_((diamond))$

$S_((rhombic))⇄S_((monoclinic))$

$P_((white))⇄P_((red))$

$Sn_((white tin))⇄Sn_((grey tin))$

$3O_(2(oxygen))⇄2O_(3(ozone))$.

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, because. isostructure hydrocarbons are less prone to detonation.

2. Alkene isomerization.

3. Alkyne isomerization(reaction of A. E. Favorsky).

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

5. Isomerization of ammonium cyanate on heating.

For the first time, urea was synthesized by F. Wehler in 1882 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- These are reactions in which two or more substances form one complex substance.

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

1) obtaining sulfur oxide (IV):

$S+O_2=SO_2$ — one complex substance is formed from two simple substances;

2) production of sulfur oxide (VI):

$2SO_2+O_2(⇄)↖(t,p,cat.)2SO_3$ - one complex substance is formed from simple and complex substances;

3) obtaining sulfuric acid:

$SO_3+H_2O=H_2SO_4$ — one compound 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:

$4NO_2+O_2+2H_2O=4HNO_3$.

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 - addition of hydrogen:

$CH_2(=)↙(ethene)CH_2+H_2(→)↖(Ni,t°)CH_3(-)↙(ethane)CH_3;$

2) hydration reaction - addition of water:

$CH_2(=)↙(ethene)CH_2+H_2O(→)↖(H_3PO_4,t°)(C_2H_5OH)↙(ethanol);$

3) polymerization reaction:

$(nCH_2=CH_2)↙(ethylene)(→)↖(p,cat.,t°)((-CH_2-CH_2-)_n)↙(polyethylene)$

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

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

1) decomposition of mercury oxide (II):

$2HgO(→)↖(t°)2Hg+O_2$ — two simple substances are formed from one complex substance;

2) decomposition of potassium nitrate:

$2KNO_3(→)↖(t°)2KNO_2+O_2$ — from one complex substance one simple and one complex substance are formed;

3) decomposition of potassium permanganate:

$2KMnO_4(→)↖(t°)K_2MnO_4+MnO_2+O_2$ — from one complex substance two complex and one simple are formed, i.e. three new substances.

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

1) the reaction of dehydration (water splitting) of ethanol:

$C_2H_5OH(→)↖(H_2SO_4,t°)CH_2=CH_2+H_2O;$

2) the reaction of dehydrogenation (hydrogen elimination) of ethane:

$CH_3—CH_3(→)↖(Cr_2O_3,500°C)CH_2=CH_2+H_2;$

3) propane cracking (splitting) reaction:

$CH_3-CH_2CH_3(→)↖(t°)CH_2=CH_2+CH_4.$

3. Substitution reactions- these are reactions in 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 and alkaline earth metals with water:

$2Na+2H_2O=2NaOH+H_2$

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) metallothermy:

$2Al+Cr_2O_3(→)↖(t°)Al_2O_3+2Cr$.

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:

$CH_4+Cl_2(→)↖(hν)(CH_3Cl)↙(chloromethane)+HCl$,

$CH_3Cl+Cl_2→(CH_2Cl_2)↙(dichloromethane)+HCl$,

$CH_2Cl_2+Cl_2→(CHCl_3)↙(trichloromethane)+HCl$,

$CHCl_3+Cl_2→(CCl_4)↙(tetrachloromethane)+HCl$.

Another example is the bromination of an aromatic compound (benzene, toluene, aniline):

Let us pay attention to the peculiarity of substitution reactions 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:

$C_6H_6+(HNO_3)↙(benzene)(→)↖(H_2SO_4(conc.),t°)(C_6H_5NO_2)↙(nitrobenzene)+H_2O$

It is formally an exchange reaction. The fact that this is a substitution reaction becomes clear only when considering its mechanism.

4. Exchange reactions- these are 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, i.e. only if the result is a precipitate, a gas, or a low-dissociation substance (for example, $H_2O$).

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

1) a neutralization reaction that goes with the formation of salt and water:

$NaOH+HNO_3=NaNO_3+H_2O$

or in ionic form:

$OH^(-)+H^(+)=H_2O$;

2) the reaction between alkali and salt, which goes with the formation of gas:

$2NH_4Cl+Ca(OH)_2=CaCl_2+2NH_3+2H_2O$

or in ionic form:

$NH_4^(+)+OH^(-)=NH_3+H_2O$;

3) the reaction between alkali and salt, which proceeds with the formation of a precipitate:

$CuSO_4+2KOH=Cu(OH)_2↓+K_2SO_4$

or in ionic form:

$Cu^(2+)+2OH^(-)=Cu(OH)_2↓$

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

1) a reaction proceeding with the formation of a weak electrolyte - $H_2O$:

$CH_3COOH+NaOH⇄NaCH_3COO+H_2O$

$CH_3COOH+OH^(-)⇄CH_3COO^(-)+H_2O$;

2) the reaction proceeding with the formation of gas:

$2CH_3COOH+CaCO_3=2CH_3COO^(-)+Ca^(2+)+CO_2+H_2O$;

3) reaction proceeding with the formation of a precipitate:

$2CH_3COOH+K_2SiO_3=2KCH_3COO+H_2SiO_3↓$

$2CH_3COOH+SiO_3^(−)=2CH_3COO^(−)+H_2SiO_3↓$.

Classification of chemical reactions according to the change in the oxidation states of chemical elements that form substances

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.$(Mg)↖(0)+(2H)↖(+1)+SO_4^(-2)=(Mg)↖(+2)SO_4+(H_2)↖(0)$

$((Mg)↖(0)-2(e)↖(-))↙(reducing agent)(→)↖(oxidation)(Mg)↖(+2)$

$((2H)↖(+1)+2(e)↖(-))↙(oxidizer)(→)↖(reduction)(H_2)↖(0)$

2.$(2Mg)↖(0)+(O_2)↖(0)=(2Mg)↖(+2)(O)↖(-2)$

$((Mg)↖(0)-2(e)↖(-))↙(reductant)(→)↖(oxidation)(Mg)↖(+2)|4|2$

$((O_2)↖(0)+4(e)↖(-))↙(oxidizer)(→)↖(reduction)(2O)↖(-2)|2|1$

As you remember, complex redox reactions are compiled using the electron balance method:

$(2Fe)↖(0)+6H_2(S)↖(+6)O_(4(k))=(Fe_2)↖(+3)(SO_4)_3+3(S)↖(+4)O_2+ 6H_2O$

$((Fe)↖(0)-3(e)↖(-))↙(reducing agent)(→)↖(oxidation)(Fe)↖(+3)|2$

$((S)↖(+6)+2(e)↖(-))↙(oxidizer)(→)↖(reduction)(S)↖(+4)|3$

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

1. Aldehydes are reduced to the corresponding alcohols:

$(CH_3-(C)↖(+1) ()↖(O↖(-2))↙(H↖(+1))+(H_2)↖(0))↙(\text"acetaldehyde") (→)↖(Ni,t°)(CH_3-(C)↖(-1)(H_2)↖(+1)(O)↖(-2)(H)↖(+1))↙(\text "ethyl alcohol")$

$((C)↖(+1)+2(e)↖(-))↙(oxidizer)(→)↖(reduction)(C)↖(-1)|1$

$((H_2)↖(0)-2(e)↖(-))↙(reductant)(→)↖(oxidation)2(H)↖(+1)|1$

2. Aldehydes are oxidized to the corresponding acids:

$(CH_3-(C)↖(+1) ()↖(O↖(-2))↙(H↖(+1))+(Ag_2)↖(+1)(O)↖(-2)) ↙(\text"acetaldehyde")(→)↖(t°)(CH_3-(Ag)↖(0)(C)↖(+3)(O)↖(-2)(OH)↖(-2 +1)+2(Ag)↖(0)↓)↙(\text"ethyl alcohol")$

$((C)↖(+1)-2(e)↖(-))↙(reducing agent)(→)↖(oxidation)(C)↖(+3)|1$

$(2(Ag)↖(+1)+2(e)↖(-))↙(oxidizer)(→)↖(reduction)2(Ag)↖(0)|1$

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:

$Li_2O+H_2O=2LiOH;$

• many decomposition reactions:

$2Fe(OH)_3(→)↖(t°)Fe_2O_3+3H_2O;$

• esterification reactions:

$HCOOH+CH_3OH⇄HCOOCH_3+H_2O$.

Classification of chemical reactions by thermal effect

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

exothermic reactions.

These 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:

$N_2+O_2=2NO - Q$,

$H_(2(t))+I(2(t))=2HI - Q$.

Exothermic reactions that proceed with the release of light are referred to as combustion reactions, for example:

$4P+5O_2=2P_2O_5+Q,$

$CH_4+2O_2=CO_2+2H_2O+Q$.

The hydrogenation of ethylene is an example of an exothermic reaction:

$CH_2=CH_2+H_2(→)↖(Pt)CH_3-CH_3+Q$

It runs at room temperature.

Endothermic reactions

These reactions proceed with the absorption of energy.

Obviously, almost all decomposition reactions belong to them, for example:

a) burning limestone:

$CaCO_3(→)↖(t°)CaO+CO_2-Q;$

b) butane cracking:

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

$H_(2(g))+Cl_(2(g))=2HCl_((g))+92.3 kJ,$

$N_(2(g))+O_(2(g))=2NO_((g)) - 90.4 kJ$.

Classification of chemical reactions according to the state of aggregation of reacting substances (phase composition)

heterogeneous reactions.

These are reactions in which the reactants and reaction products are in different states of aggregation (in different phases):

$2Al_((m))+3CuCl_(2(r-r))=3Cu_((t))+2AlCl_(3(r-r))$,

$CaC_(2(t))+2H_2O_((l))=C_2H_2+Ca(OH)_(2(solid))$.

homogeneous reactions.

These are reactions in which the reactants and reaction products are in the same state of aggregation (in the same phase):

Classification of chemical reactions according to the participation of a catalyst

non-catalytic reactions.

Non-catalytic reactions go without the participation of a catalyst:

$2HgO(→)↖(t°)2Hg+O_2$,

$C_2H_4+3O_2(→)↖(t°)2CO_2+2H_2O$.

catalytic reactions.

catalytic reactions going on with a catalyst:

$2KClO_3(→)↖(MnO_2,t°)2KCl+3O_2,$

$(C_2H_5OH)↙(ethanol)(→)↖(H_2SO-4,t°)(CH_2=CH_2)↙(ethene)+H_2O$

Since all biological reactions occurring in the cells of living organisms proceed with the participation of special biological catalysts of a protein nature - enzymes, they all belong to catalytic or, more precisely, enzymatic.

It should be noted that more than $70%$ of chemical industries use catalysts.

Classification of chemical reactions by direction

irreversible reactions.

irreversible reactions flow under these 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.

reversible reactions.

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. Reversibility underlies the most important process in a living organism - metabolism.

DEFINITION

Chemical reaction called the transformation of substances in which there is a change in their composition and (or) structure.

Most often, chemical reactions are understood as the process of transformation of initial substances (reagents) into final substances (products).

Chemical reactions are written using chemical equations containing the formulas of the starting materials and reaction products. According to the law of conservation of mass, the number of atoms of each element in the left and right sides of the chemical equation is the same. Usually, the formulas of the starting substances are written on the left side of the equation, and the formulas of the products are written on the right. The equality of the number of atoms of each element in the left and right parts of the equation is achieved by placing integer stoichiometric coefficients in front of the formulas of substances.

Chemical equations may contain additional information about the features of the reaction: temperature, pressure, radiation, etc., which is indicated by the corresponding symbol above (or “under”) the equals sign.

All chemical reactions can be grouped into several classes, which have certain characteristics.

Classification of chemical reactions according to the number and composition of the initial and resulting substances

According to this classification, chemical reactions are divided into reactions of combination, decomposition, substitution, exchange.

As a result compound reactions from two or more (complex or simple) substances, one new substance is formed. In general, the equation for such a chemical reaction will look like this:

For example:

CaCO 3 + CO 2 + H 2 O \u003d Ca (HCO 3) 2

SO 3 + H 2 O \u003d H 2 SO 4

2Mg + O 2 \u003d 2MgO.

2FeCl 2 + Cl 2 = 2FeCl 3

Combination reactions are in most cases exothermic, i.e. flow with the release of heat. If simple substances are involved in the reaction, then such reactions are most often redox (ORD), i.e. occur with a change in the oxidation states of the elements. It is impossible to say unequivocally whether the reaction of a compound between complex substances can be attributed to OVR.

Reactions in which several other new substances (complex or simple) are formed from one complex substance are classified as decomposition reactions. In general, the equation for a chemical decomposition reaction will look like this:

For example:

CaCO 3 CaO + CO 2 (1)

2H 2 O \u003d 2H 2 + O 2 (2)

CuSO 4 × 5H 2 O \u003d CuSO 4 + 5H 2 O (3)

Cu (OH) 2 \u003d CuO + H 2 O (4)

H 2 SiO 3 \u003d SiO 2 + H 2 O (5)

2SO 3 \u003d 2SO 2 + O 2 (6)

(NH 4) 2 Cr 2 O 7 \u003d Cr 2 O 3 + N 2 + 4H 2 O (7)

Most decomposition reactions proceed with heating (1,4,5). Decomposition by electric current is possible (2). The decomposition of crystalline hydrates, acids, bases and salts of oxygen-containing acids (1, 3, 4, 5, 7) proceeds without changing the oxidation states of the elements, i.e. these reactions do not apply to OVR. OVR decomposition reactions include the decomposition of oxides, acids and salts formed by elements in higher oxidation states (6).

Decomposition reactions are also found in organic chemistry, but under other names - cracking (8), dehydrogenation (9):

C 18 H 38 \u003d C 9 H 18 + C 9 H 20 (8)

C 4 H 10 \u003d C 4 H 6 + 2H 2 (9)

At substitution reactions a simple substance interacts with a complex one, forming a new simple and a new complex substance. In general, the equation for a chemical substitution reaction will look like this:

For example:

2Al + Fe 2 O 3 \u003d 2Fe + Al 2 O 3 (1)

Zn + 2HCl = ZnCl 2 + H 2 (2)

2KBr + Cl 2 \u003d 2KCl + Br 2 (3)

2KSlO 3 + l 2 = 2KlO 3 + Cl 2 (4)

CaCO 3 + SiO 2 \u003d CaSiO 3 + CO 2 (5)

Ca 3 (RO 4) 2 + ZSiO 2 = ZCaSiO 3 + P 2 O 5 (6)

CH 4 + Cl 2 = CH 3 Cl + Hcl (7)

Substitution reactions are mostly redox reactions (1 - 4, 7). Examples of decomposition reactions in which there is no change in oxidation states are few (5, 6).

Exchange reactions called the reactions that occur between complex substances, in which they exchange their constituent parts. Usually this term is used for reactions involving ions in aqueous solution. In general, the equation for a chemical exchange reaction will look like this:

AB + CD = AD + CB

For example:

CuO + 2HCl \u003d CuCl 2 + H 2 O (1)

NaOH + HCl \u003d NaCl + H 2 O (2)

NaHCO 3 + HCl \u003d NaCl + H 2 O + CO 2 (3)

AgNO 3 + KBr = AgBr ↓ + KNO 3 (4)

CrCl 3 + ZNaOH = Cr(OH) 3 ↓+ ZNaCl (5)

Exchange reactions are not redox. A special case of these exchange reactions is neutralization reactions (reactions of interaction of acids with alkalis) (2). Exchange reactions proceed in the direction where at least one of the substances is removed from the reaction sphere in the form of a gaseous substance (3), a precipitate (4, 5) or a poorly dissociating compound, most often water (1, 2).

Classification of chemical reactions according to changes in oxidation states

Depending on the change in the oxidation states of the elements that make up the reactants and reaction products, all chemical reactions are divided into redox (1, 2) and those occurring without changing the oxidation state (3, 4).

2Mg + CO 2 \u003d 2MgO + C (1)

Mg 0 - 2e \u003d Mg 2+ (reductant)

C 4+ + 4e \u003d C 0 (oxidizing agent)

FeS 2 + 8HNO 3 (conc) = Fe(NO 3) 3 + 5NO + 2H 2 SO 4 + 2H 2 O (2)

Fe 2+ -e \u003d Fe 3+ (reductant)

N 5+ + 3e \u003d N 2+ (oxidizing agent)

AgNO 3 + HCl \u003d AgCl ↓ + HNO 3 (3)

Ca(OH) 2 + H 2 SO 4 = CaSO 4 ↓ + H 2 O (4)

Classification of chemical reactions by thermal effect

Depending on whether heat (energy) is released or absorbed during the reaction, all chemical reactions are conditionally divided into exo - (1, 2) and endothermic (3), respectively. The amount of heat (energy) released or absorbed during a reaction is called the heat of the reaction. If the equation indicates the amount of released or absorbed heat, then such equations are called thermochemical.

N 2 + 3H 2 = 2NH 3 +46.2 kJ (1)

2Mg + O 2 \u003d 2MgO + 602.5 kJ (2)

N 2 + O 2 \u003d 2NO - 90.4 kJ (3)

Classification of chemical reactions according to the direction of the reaction

According to the direction of the reaction, there are reversible (chemical processes, the products of which are able to react with each other under the same conditions in which they are obtained, with the formation of starting substances) and irreversible (chemical processes, the products of which are not able to react with each other with the formation of starting substances ).

For reversible reactions, the equation in general form is usually written as follows:

A + B ↔ AB

For example:

CH 3 COOH + C 2 H 5 OH ↔ H 3 COOS 2 H 5 + H 2 O

Examples of irreversible reactions are the following reactions:

2KSlO 3 → 2KSl + ZO 2

C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O

Evidence of the irreversibility of the reaction can serve as the reaction products of a gaseous substance, a precipitate or a low-dissociating compound, most often water.

Classification of chemical reactions by the presence of a catalyst

From this point of view, catalytic and non-catalytic reactions are distinguished.

A catalyst is a substance that speeds up a chemical reaction. Reactions involving catalysts are called catalytic. Some reactions are generally impossible without the presence of a catalyst:

2H 2 O 2 \u003d 2H 2 O + O 2 (MnO 2 catalyst)

Often, one of the reaction products serves as a catalyst that accelerates this reaction (autocatalytic reactions):

MeO + 2HF \u003d MeF 2 + H 2 O, where Me is a metal.

Examples of problem solving

EXAMPLE 1

Classification of chemical reactions

Abstract on chemistry of a student of the 11th grade of secondary school No. 653 Alexey Nikolaev

The following can be selected as classification features:

1. The number and composition of the starting materials and reaction products.

2. Aggregate state of reactants and reaction products.

3. The number of phases in which the participants in the reaction are.

4. The nature of the carried particles.

5. The possibility of a reaction proceeding in the forward and reverse direction.

6. thermal effect.

7. The phenomenon of catalysis.

Classification according to the number and composition of the starting substances and reaction products.

Connection reactions.

In the reactions of a compound from several reacting substances of a relatively simple composition, one substance of a more complex composition is obtained:

A+B+C=D

As a rule, these reactions are accompanied by heat release, i.e. lead to the formation of more stable and less energy-rich compounds.

Inorganic chemistry.

The reactions of the combination of simple substances are always redox in nature. Connection reactions occurring between complex substances can occur both without a change in valence:

CaCO 3 + CO 2 + H 2 O \u003d Ca (HCO 3) 2,

and be classified as redox:

2FeCl 2 + Cl 2 = 2FeCl 3.

Organic chemistry.

In organic chemistry, such reactions are often called addition reactions. They usually involve compounds containing a double or triple bond. Varieties of addition reactions: hydrogenation, hydration, hydrohalogenation, polymerization. Examples of these reactions:

T o

H 2 C \u003d CH 2 + H 2 → CH 3 - CH 3

ethylene ethane

T o

HC=CH + HCl → H 2 C=CHCl

acetylene vinyl chloride

T o

n CH 2 \u003d CH 2 → (-CH 2 -CH 2 -) n

Ethylene polyethylene

decomposition reactions.

Decomposition reactions lead to the formation of several compounds from one complex substance:

A = B + C + D.

The decomposition products of a complex substance can be both simple and complex substances.

Inorganic chemistry.

Of the decomposition reactions that occur without changing the valence states, the decomposition of crystalline hydrates, bases, acids and salts of oxygen-containing acids should be noted:

	t o
CuSO 4 5H 2 O		CuSO 4 + 5H 2 O

	t o
4HNO 3		2H 2 O + 4NO 2 O + O 2 O.

2AgNO 3 \u003d 2Ag + 2NO 2 + O 2,

(NH 4) 2Cr 2 O 7 \u003d Cr 2 O 3 + N 2 + 4H 2 O.

Organic chemistry.

In organic chemistry, decomposition reactions include: dehydration, dehydrogenation, cracking, dehydrohalogenation, as well as depolymerization reactions, when the initial monomer is formed from the polymer. The corresponding reaction equations are:

T o

C 2 H 5 OH → C 2 H 4 + H 2 O

T o

C 6 H 14 → C 6 H 6 + 4H 2

hexane benzene

C 8 H 18 → C 4 H 10 + C 4 H 8

Octane Butane Butene

C 2 H5Br → C 2 H 4 + HBr

bromoethane ethylene

(-CH 2 - CH \u003d C - CH 2 -) n → n CH 2 \u003d CH - C \u003d CH 2

\CHz \CHz

natural rubber 2-methylbutadiene-1,3

substitution reactions.

In substitution reactions, usually a simple substance interacts with a complex one, forming another simple substance and another complex one:

A + BC = AB + C.

Inorganic chemistry.

These reactions in the vast majority belong to redox reactions:

2Al + Fe 2 O 3 \u003d 2Fe + Al 2 O 3

Zn + 2HCl = ZnCl 2 + H 2

2KBr + Cl 2 \u003d 2KCl + Br 2

2 KS lO 3 + l 2 \u003d 2KlO 3 + C l 2.

Examples of substitution reactions that are not accompanied by a change in the valence states of atoms are extremely few. It should be noted the reaction of silicon dioxide with salts of oxygen-containing acids, which correspond to gaseous or volatile anhydrides:

CaCO 3 + SiO 2 \u003d CaSiO 3 + CO 2

Ca 3 (RO 4) 2 + ZSiO 2 = ZCaSiO 3 + P 2 O 5

Organic chemistry.

In organic chemistry, substitution reactions are understood more broadly, that is, not one atom can replace, but a group of atoms, or not an atom, but a group of atoms is replaced. A variety of substitution reactions include nitration and halogenation of saturated hydrocarbons, aromatic compounds and alcohols:

C 6 H 6 + Br 2 → C 6 H 5 Br + HBr

benzene bromobenzene

C 2 H 5 OH + HCl → C 2 H 5 Cl + H 2 O

Ethanol chloroethane

Exchange reactions.

Exchange reactionsReactions between two compounds that exchange their constituents are called:

AB + CD = AD + CB.

Inorganic chemistry

If redox processes occur during substitution reactions, then exchange reactions always occur without changing the valence state of atoms. This is the most common group of reactions between complex substances - oxides, bases, acids and salts:

ZnO + H 2 SO 4 \u003d ZnSO 4 + H 2 O

AgNO 3 + KBr = AgBr + KNO 3

CrCl 3 + ZNaOH = Cr(OH) 3 + ZNaCl.

A special case of these exchange reactions is neutralization reactions:

Hcl + KOH \u003d KCl + H 2 O.

Usually, these reactions obey the laws of chemical equilibrium and proceed in the direction where at least one of the substances is removed from the reaction sphere in the form of a gaseous, volatile substance, precipitate, or low-dissociation (for solutions) compound:

NaHCO 3 + HCl \u003d NaCl + H 2 O + CO 2

Ca (HCO 3) 2 + Ca (OH) 2 \u003d 2CaCO 3 ↓ + 2H 2 O

Organic chemistry

HCOOH + NaOH → HCOONa + H 2 O

formic acid sodium formate

hydrolysis reactions:

Na 2 CO3 + H 2 O
NaHCO3 + NaOH

sodium carbonate sodium bicarbonate

CO 3 + H 2 O
HCO 3 + OH

esterification reactions:

CH 3 COOH + C 2 H 5 OH
CH 3 COOC 2 H 5 + H 2 O

acetic ethanol ethyl acetate

Aggregate state of reactants and reaction products.

Gas reactions

	t o
H 2 + Cl 2		2HCl.

Reactions in solutions

NaOH (pp) + Hcl (p-p) \u003d NaCl (p-p) + H 2 O (l)

Reactions between solids

	t o
CaO (tv) + SiO 2 (tv)		CaSiO 3 (TV)

The number of phases in which the participants in the reaction are.

A phase is understood as a set of homogeneous parts of a system with the same physical and chemical properties and separated from each other by an interface.

Homogeneous (single-phase) reactions.

These include reactions occurring in the gas phase, and a number of reactions occurring in solutions.

Heterogeneous (multiphase) reactions.

These include reactions in which the reactants and products of the reaction are in different phases. For example:

gas-liquid phase reactions

CO 2 (g) + NaOH (p-p) = NaHCO 3 (p-p).

gas-solid-phase reactions

CO 2 (g) + CaO (tv) \u003d CaCO 3 (tv).

liquid-solid-phase reactions

Na 2 SO 4 (pp) + BaCl 3 (pp) \u003d BaSO 4 (tv) ↓ + 2NaCl (p-p).

liquid-gas-solid-phase reactions

Ca (HCO 3) 2 (pp) + H 2 SO 4 (pp) \u003d CO 2 (r) + H 2 O (l) + CaSO 4 (tv) ↓.

The nature of the carried particles.

protolytic reactions.

Protolytic reactions include chemical processes, the essence of which is the transfer of a proton from one reactant to another.

This classification is based on the protolytic theory of acids and bases, according to which any substance that donates a proton is considered an acid, and a substance capable of accepting a proton is considered a base, for example:

Protolytic reactions include neutralization and hydrolysis reactions.

Redox reactions.

All chemical reactions are divided into those in which the oxidation states do not change (for example, the exchange reaction) and those in which the oxidation states change. They are called redox reactions. They can be decomposition reactions, compounds, substitutions and other more complex reactions. For example:

Zn + 2 H + → Zn 2 + + H 2

FeS 2 + 8HNO 3 (conc ) \u003d Fe (NO 3) 3 + 5NO + 2H 2 SO 4 + 2H 2 O

The vast majority of chemical reactions are redox, they play an extremely important role.

ligand exchange reactions.

These include reactions during which the transfer of an electron pair occurs with the formation of a covalent bond by the donor-acceptor mechanism. for example:

Cu(NO 3) 2 + 4NH 3 = (NO 3) 2

Fe + 5CO =

Al(OH) 3 + NaOH =

A characteristic feature of ligand-exchange reactions is that the formation of new compounds, called complex ones, occurs without a change in the oxidation state.

The possibility of a reaction proceeding in the forward and reverse direction.

irreversible reactions.

irreversible called such chemical processes, the products of which are not able to react with each other with the formation of starting substances. Examples of irreversible reactions are the decomposition of Bertolet salt when heated:

2KSlO 3 → 2KSl + ZO 2,

or oxidation of glucose with atmospheric oxygen:

C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O

reversible reactions.

reversible called such chemical processes, the products of which are able to react with each other under the same conditions in which they are obtained, with the formation of starting substances.

For reversible reactions, the equation is usually written as follows:

A+B
AB.

Two oppositely directed arrows indicate that under the same conditions, both forward and reverse reactions proceed simultaneously, for example:

CH 3 COOH + C 2 H 5 OH
CH 3 COOS 2 H 5 + H 2 O.

2SO2 +O2
2SO 3 + Q

Consequently, these reactions do not go to the end, because two reactions occur simultaneously - direct (between the starting materials) and reverse (decomposition of the reaction product).

Classification by thermal effect.

The amount of heat that is released or absorbed as a result of a reaction is called the thermal effect of this reaction. According to the thermal effect of the reaction, they are divided into:

exothermic.

Flow with heat

CH 4 + 2O 2 → CO 2 + 2H 2 O + Q

H 2 + Cl 2 → 2HC l + Q

Endothermic.

Flow with heat absorption

N 2 + O 2 → 2NO-Q

2Н 2 O → 2Н 2 + O 2 - Q

Classification taking into account the phenomenon of catalysis.

catalytic.

These include all processes involving catalysts.

Cat.

2SO2 + O2
2SO3

Non-catalytic.

These include any instantaneous reactions in solutions

BaCl 2 + H 2 SO 4 \u003d 2HCl + BaSO 4 ↓

Bibliography

Internet resources:

http://chem.km.ru - "World of Chemistry"

http:// chemi. org. ru – “Manual for applicants. Chemistry"

http://hemi. wallst. ru - "Alternative textbook in chemistry for grades 8-11"

"Guide to Chemistry. Applicants to universities "- E.T. Hovhannisyan, M. 1991

Big Encyclopedic Dictionary. Chemistry "- M. 1998.

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. Nuclear reactions are another matter - the processes of transformation of atomic nuclei as a result of their interaction with other nuclei or elementary particles, for example, the transformation of aluminum into 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, there are reactions of addition of hydrogen halides, hydrogen, halogens to alkenes, oxidation and dehydration of alcohols, replacement of alcohol hydroxyl by halogen; 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 by an electric current. In addition to the electrolysis reactions well known to you, we 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.

In inorganic chemistry, chemical reactions are classified according to different criteria.

1. By changing the oxidation state to redox, which go with a change in the oxidation state of the elements and acid-base, which proceed without changing the oxidation states.

2. By the nature of the process.

Decomposition reactions are chemical reactions in which simple molecules are formed from more complex ones.

Connection reactions chemical reactions are called, in which complex compounds are obtained from several simpler ones.

Substitution reactions are chemical reactions in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms.

Exchange reactions called chemical reactions that occur without changing the oxidation state of the elements and leading to the exchange of constituent parts of the reagents.

3. If possible, proceed in the opposite direction to reversible and irreversible.

Some reactions, such as the combustion of ethanol, are practically irreversible, i.e. it is impossible to create conditions for it to flow in the opposite direction.

However, there are many reactions that, depending on the process conditions, can proceed both in the forward and reverse directions. Reactions that can proceed in both the forward and reverse directions are called reversible.

4. According to the type of bond rupture - homolytic(equal gap, each atom gets one electron) and heterolytic(unequal gap - one gets a pair of electrons).

5. According to the thermal effect, exothermic(heat release) and endothermic(heat absorption).

Combination reactions will generally be exothermic reactions, while decomposition reactions will be endothermic. A rare exception is the endothermic reaction of nitrogen with oxygen N 2 + O 2 = 2NO - Q.

6. According to the state of aggregation of the phases.

homogeneous(the reaction takes place in one phase, without interfaces; reactions in gases or in solutions).

Heterogeneous(reactions taking place at the phase boundary).

7. By using a catalyst.

A catalyst is a substance that speeds up a chemical reaction but remains chemically unchanged.

catalytic practically do not go without the use of a catalyst and non-catalytic.

Classification of organic reactions

Reaction type	Radical	Nucleophilic (N)	Electrophilic (e)
Substitution (S)	radical substitution (S R)	Nucleophilic substitution (S N)	Electrophilic substitution (S E)
Connection (A)	radical connection (A R)	Nucleophilic addition (A N)	Electrophilic addition (A E)
Cleavage (E) (elimination)	radical cleavage (E R)	Nucleophilic cleavage (E N)	Electrophilic elimination (E E)

Electrophilic refers to heterolytic reactions of organic compounds with electrophiles - particles that carry a whole or fractional positive charge. They are subdivided into electrophilic substitution and electrophilic addition reactions. For example,

H 2 C \u003d CH 2 + Br 2  BrCH 2 - CH 2 Br

Nucleophilic refers to heterolytic reactions of organic compounds with nucleophiles - particles that carry an integer or fractional negative charge. They are subdivided into nucleophilic substitution and nucleophilic addition reactions. For example,

CH 3 Br + NaOH  CH 3 OH + NaBr

Radical (chain) reactions are called chemical reactions involving radicals, for example