What are compound reactions. Classification of chemical reactions

Part I

1. Compound reactions are The "chemical antonym" of the decomposition reaction.

2. Record the signs of the reaction of the compound:
- 2 simple or complex substances are involved in the reaction;
- one complex is formed;
- heat is generated.

3. Based on the selected features, define the reactions of the compound.
Compound reactions are reactions resulting in the formation of one complex from one or more simple or complex substances.

According to the direction of the reaction, they are divided into:

Part II

1. Write down the equations chemical reactions:

2. Write the equations of chemical reactions between chlorine:
1) and sodium 2Na + Cl2 = 2NaCl
2) and calcium Ca + Cl2 = CaCl2
3) and iron with the formation of iron (III) chloride 2Fe + 3Cl2 = 2FeCl3

3. Describe the reaction

4. Describe the reaction

5. Write down the equations of the reactions of the compound proceeding according to the schemes:

6. Place the coefficients in the reaction equations, the schemes of which:

7. Are the following judgments correct?
A. Most compound reactions are exothermic.
B. As the temperature rises, the rate of the chemical reaction increases.
1) both judgments are correct

8. Calculate the volume of hydrogen and the mass of sulfur required to form 85 g of hydrogen sulfide.

The chemical properties of substances are revealed in a variety of chemical reactions.

Transformations of substances, accompanied by a change in their composition and (or) structure, are called chemical reactions... The following definition is often found: chemical reaction is the process of converting initial substances (reagents) into final substances (products).

Chemical reactions are written using chemical equations and diagrams containing formulas for the starting materials and reaction products. V chemical equations, in contrast to the schemes, the number of atoms of each element is the same on the left and right sides, which reflects the law of conservation of mass.

On the left side of the equation, the formulas of the initial substances (reagents) are written, on the right side - the substances obtained as a result of a chemical reaction (reaction products, final substances). The equal sign connecting the left and right side, indicates that the total number of atoms of the substances participating in the reaction remains constant. This is achieved by placing integer stoichiometric coefficients in front of the formulas, showing the quantitative ratios between reagents and reaction products.

Chemical equations can contain additional information about the features of the reaction. If a chemical reaction occurs under the influence external influences(temperature, pressure, radiation, etc.), this is indicated by the appropriate symbol, usually above (or “below”) the equal sign.

A huge number of chemical reactions can be grouped into several types of reactions, which have well-defined characteristics.

As classification signs the following can be selected:

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

2. Aggregate state of reagents and reaction products.

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

4. The nature of the transported particles.

5. Possibility of the reaction proceeding in the forward and reverse direction.

6. The sign of the thermal effect separates all reactions into: exothermic reactions proceeding with the exo-effect - the release of energy in the form of heat (Q> 0, ∆H<0):

C + O 2 = CO 2 + Q

and endothermic reactions proceeding with the endo-effect - the absorption of energy in the form of heat (Q<0, ∆H >0):

N 2 + O 2 = 2NO - Q.

Such reactions are referred to as thermochemical.

Let's consider in more detail each of the types of reactions.

Classification according to the number and composition of reagents and final substances

1. Compound 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:

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

The reactions of the compound of simple substances are always of a redox nature. Compound reactions occurring between complex substances can occur as without changing the valence:

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

and refer to the number of redox:

2FeCl 2 + Cl 2 = 2FeCl 3.

2. Decomposition reactions

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

A = B + C + D.

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

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

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

2AgNO 3 = 2Ag + 2NO 2 + O 2,
(NH 4) 2Cr 2 O 7 = Cr 2 O 3 + N 2 + 4H 2 O.

Redox decomposition reactions are especially characteristic for nitric acid salts.

Decomposition reactions in organic chemistry are called cracking:

C 18 H 38 = C 9 H 18 + C 9 H 20,

or dehydrogenation

C 4 H 10 = C 4 H 6 + 2H 2.

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.

These reactions overwhelmingly belong to redox reactions:

2Аl + Fe 2 O 3 = 2Fе + Аl 2 О 3,

Zn + 2HCl = ZnCl 2 + H 2,

2KBr + Cl 2 = 2KCl + Br 2,

2KLO 3 + l 2 = 2KlO 3 + Cl 2.

Examples of substitution reactions 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 = CaSiO 3 + CO 2,

Ca 3 (PO 4) 2 + ЗSiO 2 = ЗСаSiO 3 + Р 2 О 5,

Sometimes these reactions are considered as exchange reactions:

CH 4 + Cl 2 = CH 3 Cl + HCl.

4. Exchange reactions

Exchange reactions call the reactions between two compounds that exchange their constituent parts with each other:

AB + CD = AD + CB.

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 + Н 2 SO 4 = ZnSО 4 + Н 2 О,

AgNO 3 + KBr = AgBr + KNO 3,

CrCl 3 + 3NaOH = Cr (OH) 3 + 3NaCl.

A special case of these exchange reactions is neutralization reactions:

HCl + KOH = 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, a precipitate or a compound that is poorly dissociated (for solutions):

NaHCO 3 + HCl = NaCl + H 2 O + CO 2,

Ca (HCO 3) 2 + Ca (OH) 2 = 2CaCO 3 ↓ + 2H 2 O,

CH 3 COONa + H 3 PO 4 = CH 3 COOH + NaH 2 PO 4.

5. Transfer reactions.

In transfer reactions, an atom or a group of atoms passes from one structural unit to another:

AB + BC = A + B 2 C,

А 2 В + 2СВ 2 = АСВ 2 + АСВ 3.

For example:

2AgCl + SnCl 2 = 2Ag + SnCl 4,

H 2 O + 2NO 2 = HNO 2 + HNO 3.

Phase classification of reactions

Depending on the state of aggregation of the reacting substances, the following reactions are distinguished:

1. Gas reactions


H 2 + Cl 2		2HCl.

2. Reactions in solutions

NaOH (p-p) + HCl (p-p) = NaCl (p-p) + H 2 O (g)

3. Reactions between solids

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

Classification of reactions by the number of phases.

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.

From this point of view, the whole variety of reactions can be divided into two classes:

1.Homogeneous (single-phase) reactions. These include reactions occurring in the gas phase, and whole line reactions taking place in solutions.

2. Heterogeneous (multiphase) reactions. These include reactions in which the reactants and reaction products are in different phases. For example:

gas-liquid reactions

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

gas-solid-phase reactions

CO 2 (g) + CaO (s) = CaCO 3 (s).

liquid-solid-phase reactions

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

liquid-gas-solid-phase reactions

Ca (HCO 3) 2 (p-p) + H 2 SO 4 (p-p) = CO 2 (r) + H 2 O (g) + CaSO 4 (s) ↓.

Classification of reactions by the type of transported particles

1. Protolytic reactions.

TO protolytic reactions include chemical processes, the essence of which is the transfer of a proton from one reacting substance to another.

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

Protolytic reactions include neutralization and hydrolysis reactions.

2. Redox reactions.

These include reactions in which the reacting substances exchange electrons, while changing the oxidation state of the atoms of the elements that make up the reacting substances. For example:

Zn + 2H + → Zn 2 + + H 2,

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

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

3. Ligand exchange reactions.

These include reactions in the course of which an electron pair is transferred 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, occurs without changing the oxidation state.

4. Reactions of atomic-molecular exchange.

This type of reaction includes many of the substitution reactions studied in organic chemistry, proceeding according to a radical, electrophilic, or nucleophilic mechanism.

Reversible and irreversible chemical reactions

Such chemical processes are called reversible, the products of which are capable of reacting with each other under the same conditions in which they are obtained, with the formation of the initial substances.

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

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

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

Such chemical processes are called irreversible, the products of which are not able to react with each other with the formation of initial substances. Examples of irreversible reactions are the decomposition of berthollet's salt upon heating:

2KSlO 3 → 2KSl + 3O 2,

or oxidation of glucose with atmospheric oxygen:

C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O.