The reaction of combining two simple substances. chemical 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 heat release, i.e. lead to the formation of more stable and less energy-rich compounds.

Connection reactions 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.

2. 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.

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

2AgNO 3 \u003d 2Ag + 2NO 2 + O 2, (NH 4) 2Cr 2 O 7 \u003d Cr 2 O 3 + N 2 + 4H 2 O.

Particularly characteristic are the redox reactions of decomposition for salts of nitric acid.

Decomposition reactions in organic chemistry are called cracking:

C 18 H 38 \u003d C 9 H 18 + C 9 H 20,

or dehydrogenation

C 4 H 10 \u003d 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 in the vast majority belong to redox reactions:

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

Zn + 2HCl \u003d ZnCl 2 + H 2,

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

2KSlO 3 + l 2 = 2KlO 3 + Cl 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 \u003d ZCaSiO 3 + P 2 O 5,

Sometimes these reactions are considered as exchange reactions:

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

4. Exchange reactions

Exchange reactions are reactions between two compounds that exchange their constituents 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 + 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 the neutralization reaction:

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 gaseous, volatile matter, precipitate or low-dissociating (for solutions) compounds:

NaHCO 3 + Hcl \u003d NaCl + H 2 O + CO 2,

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

CH 3 COONa + H 3 RO 4 \u003d CH 3 COOH + NaH 2 RO 4.

Chemical properties substances are detected in various 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 The process of transformation of initial substances (reagents) into final substances (products) is called.

Chemical reactions are written using chemical equations and schemes containing the formulas of the starting materials and reaction products. IN chemical equations, unlike 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 starting 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 linking the left and right sides indicates that total atoms of the substances involved in the reaction remains constant. This is achieved by placing integer stoichiometric coefficients in front of the formulas, showing the quantitative ratios between the reactants and reaction products.

Chemical equations may contain additional information about the features of the reaction. If a chemical reaction proceeds under the influence of external influences (temperature, pressure, radiation, etc.), this is indicated by the appropriate symbol, usually above (or "under") the equals sign.

Huge number chemical reactions can be grouped into several types of reactions, which are characterized by well-defined features.

As classification features the following can be selected:

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 transferred particles.

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

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 \u003d 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 \u003d 2NO - Q.

Such reactions are thermochemical.

Let us consider in more detail each of the types of reactions.

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

1. 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:

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

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.

2. 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.

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

2AgNO 3 \u003d 2Ag + 2NO 2 + O 2,
(NH 4) 2Cr 2 O 7 \u003d Cr 2 O 3 + N 2 + 4H 2 O.

Particularly characteristic are the redox reactions of decomposition for salts of nitric acid.

Decomposition reactions in organic chemistry are called cracking:

C 18 H 38 \u003d C 9 H 18 + C 9 H 20,

or dehydrogenation

C 4 H 10 \u003d 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 in the vast majority belong to redox reactions:

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

Zn + 2HCl \u003d ZnCl 2 + H 2,

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

2KSlO 3 + l 2 = 2KlO 3 + Cl 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 \u003d ZCaSiO 3 + P 2 O 5,

Sometimes these reactions are considered as exchange reactions:

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

4. Exchange reactions

Exchange reactions Reactions between two compounds that exchange their constituents are called:

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 + 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.

Typically, 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,

CH 3 COONa + H 3 RO 4 \u003d CH 3 COOH + NaH 2 RO 4.

5. Transfer reactions.

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

AB + BC \u003d A + B 2 C,

A 2 B + 2CB 2 = DIA 2 + DIA 3.

For example:

2AgCl + SnCl 2 \u003d 2Ag + SnCl 4,

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

Classification of reactions according to phase features

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

1. Gas reactions

2. Reactions in solutions

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

3. Reactions between solids

Classification of reactions according to 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 a number of reactions occurring in solutions.

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

liquid-gas-solid-phase reactions

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

Classification of reactions according to the type of particles carried

1. Protolytic reactions.

TO 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 an acid is any substance that donates a proton, and a base is a substance that can accept a proton, for example:

Protolytic reactions include neutralization and hydrolysis reactions.

2. Redox reactions.

These include reactions in which the reactants exchange electrons, while changing the oxidation state of the atoms of the elements that make up the reactants. 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 vast majority of chemical reactions are redox, they play an extremely important role.

3. Ligand exchange reactions.

These include reactions during 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 ones, occurs without a change in the oxidation state.

4. Reactions of atomic-molecular exchange.

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

Reversible and irreversible chemical reactions

Reversible are 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:

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.

Irreversible are 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.

Many processes without which it is impossible to imagine our life (such as respiration, digestion, photosynthesis, and the like) are associated with various chemical reactions of organic compounds (and inorganic ones). Let's look at their main types and dwell in more detail on the process called connection (attachment).

What is called a chemical reaction

First of all, it is worth giving a general definition of this phenomenon. The phrase under consideration refers to various reactions of substances of varying complexity, as a result of which products different from the original ones are formed. The substances involved in this process are referred to as "reagents".

In writing, the chemical reaction of organic compounds (and inorganic ones) is written using specialized equations. Outwardly, they are a bit like mathematical examples of addition. However, instead of an equal sign ("="), arrows ("→" or "⇆") are used. In addition, there can sometimes be more substances on the right side of the equation than on the left. Everything before the arrow is the substances before the start of the reaction (left side of the formula). Everything after it (the right side) is the compounds formed as a result of the chemical process that has taken place.

As an example of a chemical equation, we can consider water into hydrogen and oxygen under the influence of an electric current: 2H 2 O → 2H 2 + O 2. Water is the initial reactant, and oxygen and hydrogen are the products.

As another, but more complex example of a chemical reaction of compounds, we can consider a phenomenon familiar to every housewife who has baked sweets at least once. We are talking about quenching baking soda with table vinegar. The ongoing action is illustrated using the following equation: NaHCO 3 +2 CH 3 COOH → 2CH 3 COONa + CO 2 + H 2 O. From it it is clear that in the process of interaction of sodium bicarbonate and vinegar, sodium salt of acetic acid, water and carbon dioxide are formed.

By its nature, it occupies an intermediate position between physical and nuclear.

Unlike the former, compounds participating in chemical reactions are able to change their composition. That is, from the atoms of one substance, several others can be formed, as in the above equation for the decomposition of water.

Unlike nuclear reactions, chemical reactions do not affect the nuclei of atoms of the interacting substances.

What are the types of chemical processes

The distribution of reactions of compounds by type occurs according to different criteria:

• Reversibility / irreversibility.
• Presence/absence of catalyzing substances and processes.
• By absorption / release of heat (endothermic / exothermic reactions).
• By the number of phases: homogeneous / heterogeneous and two hybrid varieties.
• By changing the oxidation states of the interacting substances.

Types of chemical processes in inorganic chemistry according to the method of interaction

This criterion is special. With its help, four types of reactions are distinguished: connection, substitution, decomposition (splitting) and exchange.

The name of each of them corresponds to the process that it describes. That is, they are combined, in substitution they change to other groups, in the decomposition of one reagent several are formed, and in the exchange the participants in the reaction change atoms among themselves.

Types of processes according to the method of interaction in organic chemistry

Despite the great complexity, the reactions of organic compounds occur according to the same principle as inorganic ones. However, they have somewhat different names.

So, the reactions of combination and decomposition are called “addition”, as well as “cleavage” (elimination) and directly organic decomposition (in this section of chemistry there are two types of splitting processes).

Other reactions of organic compounds are substitution (the name does not change), rearrangement (exchange) and redox processes. Despite the similarity of the mechanisms of their occurrence, in organic matter they are more multifaceted.

Chemical reaction of the compound

Having considered the various types of processes that substances enter into in organic and inorganic chemistry, it is worth dwelling in more detail on the compound.

This reaction differs from all the others in that, regardless of the number of reagents at its beginning, in the final they all combine into one.

As an example, we can recall the process of slaking lime: CaO + H 2 O → Ca (OH) 2. In this case, the reaction of the combination of calcium oxide (quicklime) with hydrogen oxide (water) occurs. As a result, calcium hydroxide (slaked lime) is formed and warm steam is released. By the way, this means that this process is really exothermic.

Compound reaction equation

Schematically, the process under consideration can be depicted as follows: A+BV → ABC. In this formula, ABV is the newly formed A - a simple reagent, and BV - a variant of a complex compound.

It is worth noting that this formula is also characteristic of the process of addition and connection.

Examples of the reaction under consideration are the interaction of sodium oxide and carbon dioxide (NaO 2 + CO 2 (t 450-550 ° C) → Na 2 CO 3), as well as sulfur oxide with oxygen (2SO 2 + O 2 → 2SO 3).

Several complex compounds are also able to react with each other: AB + VG → ABVG. For example, all the same sodium oxide and hydrogen oxide: NaO 2 + H 2 O → 2NaOH.

Reaction conditions in inorganic compounds

As was shown in the previous equation, substances of varying degrees of complexity can enter into the interaction under consideration.

In this case, for simple reagents of inorganic origin, redox reactions of the compound (A + B → AB) are possible.

As an example, we can consider the process of obtaining a trivalent. For this, a compound reaction is carried out between chlorine and ferum (iron): 3Cl 2 + 2Fe → 2FeCl 3.

If we are talking about the interaction of complex inorganic substances (AB + VG → ABVG), processes in them can occur, both affecting and not affecting their valency.

As an illustration of this, consider the example of the formation of calcium bicarbonate from carbon dioxide, hydrogen oxide (water) and white food coloring E170 (calcium carbonate): CO 2 + H 2 O + CaCO 3 → Ca (CO 3) 2. In this case, it has place a classical coupling reaction. During its implementation, the valency of the reagents does not change.

A slightly more perfect (than the first) chemical equation 2FeCl 2 + Cl 2 → 2FeCl 3 is an example of a redox process in the interaction of simple and complex inorganic reagents: gas (chlorine) and salt (iron chloride).

Types of addition reactions in organic chemistry

As already mentioned in the fourth paragraph, in substances of organic origin, the reaction in question is called "addition". As a rule, complex substances with a double (or triple) bond take part in it.

For example, the reaction between dibrom and ethylene, leading to the formation of 1,2-dibromoethane: (C 2 H 4) CH 2 \u003d CH 2 + Br 2 → (C₂H₄Br₂) BrCH 2 - CH 2 Br. By the way, signs similar to equals and minus ("=" and "-") in this equation show the bonds between the atoms of a complex substance. This is a feature of writing formulas of organic substances.

Depending on which of the compounds act as reagents, several varieties of the addition process under consideration are distinguished:

• Hydrogenation (hydrogen molecules H are added along the multiple bond).
• Hydrohalogenation (hydrogen halide is added).
• Halogenation (addition of halogens Br 2 , Cl 2 and the like).
• Polymerization (formation from several low molecular weight compounds of substances with high molecular weight).

Examples of addition reactions (compounds)

After listing the varieties of the process under consideration, it is worth learning in practice some examples of the compound reaction.

As an illustration of hydrogenation, you can pay attention to the equation for the interaction of propene with hydrogen, as a result of which propane will appear: (C 3 H 6) CH 3 -CH \u003d CH 2 + H 2 → (C 3 H 8) CH 3 -CH 2 -CH 3 .

In organic chemistry, a compound (addition) reaction can occur between hydrochloric acid and ethylene to form chloroethane: (C 2 H 4 ) CH 2 = CH 2 + HCl → CH 3 - CH 2 -Cl (C 2 H 5 Cl). The equation presented is an example of hydrohalogenation.

As for halogenation, it can be illustrated by the reaction between dichlor and ethylene leading to the formation of 1,2-dichloroethane: (C 2 H 4 ) CH 2 = CH 2 + Cl 2 → (C₂H₄Cl₂) ClCH 2 -CH 2 Cl.

Many useful substances are formed due to organic chemistry. The reaction of connection (attachment) of ethylene molecules with a radical polymerization initiator under the influence of ultraviolet is a confirmation of this: n CH 2 \u003d CH 2 (R and UV light) → (-CH 2 -CH 2 -) n. The substance formed in this way is well known to every person under the name of polyethylene.

Various types of packaging, bags, dishes, pipes, insulation materials and much more are made from this material. A feature of this substance is the possibility of its recycling. Polyethylene owes its popularity to the fact that it does not decompose, which is why environmentalists have a negative attitude towards it. However, in recent years, a way has been found to safely dispose of polyethylene products. For this, the material is treated with nitric acid (HNO 3). After that, certain types of bacteria are able to decompose this substance into safe components.

The reaction of connection (addition) plays an important role in nature and human life. In addition, it is often used by scientists in laboratories to synthesize new substances for various important studies.

Part I

1. Connection reactions are"chemical antonym" of the decomposition reaction.

2. Write down the signs of the compound reaction:
- 2 simple or complex substances participate in the reaction;
- one complex is formed;
- heat is released.

3. Based on the selected features, give a definition of the reactions of the compound.
Combination reactions are reactions that result in the formation of one complex substance 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 of 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 to form iron (III) chloride 2Fe+3Cl2=2FeCl3

3. Describe the reaction

4. Describe the reaction

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

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

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

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

Connection reactions (formation of one complex substance from several simple or complex substances) A ​​+ B \u003d AB

Decomposition reactions (decomposition of one complex substance into several simple or complex substances) AB \u003d A + B

Substitution reactions (between simple and complex substances, in which the atoms of a simple substance replace the atoms of one of the elements in a complex substance): AB + C \u003d AC + B

Exchange reactions (between two complex substances in which substances exchange their constituent parts) AB + SD \u003d AD + CB

1. Specify the correct definition of a compound reaction:

• A. The reaction of the formation of several substances from one simple substance;

• B. A reaction in which one complex substance is formed from several simple or complex substances.

• B. A reaction in which substances exchange their constituents.

2. Specify the correct definition of a substitution reaction:

• A. Reaction between base and acid;

• B. The reaction of the interaction of two simple substances;

• B. A reaction between substances in which the atoms of a simple substance replace the atoms of one of the elements in a complex substance.

3. Specify the correct definition of the decomposition reaction:

• A. A reaction in which several simple or complex substances are formed from one complex substance;

• B. A reaction in which substances exchange their constituents;

• B. Reaction with the formation of oxygen and hydrogen molecules.

4. Specify the signs of the exchange reaction:

• A. Formation of water;

• B. Gas formation only;

• B. Precipitation only;

• D. Precipitation, formation of gas, or formation of a weak electrolyte.

5. What type of reactions is the interaction of acid oxides with basic oxides:

• A. Exchange reaction;

• B. Connection reaction;

• B. Decomposition reaction;

• D. Substitution reaction.

6. What type of reaction is the interaction of salts with acids or bases:

• A. Substitution reactions;

• B. Decomposition reactions;

• B. Exchange reactions;

• D. Connection reactions.

• 7. Substances whose formulas are KNO3 FeCl2, Na2SO4 are called:

• A) salts B) grounds; B) acids D) oxides.

• 8 . Substances whose formulas are HNO3, HCl, H2SO4 are called:

• 9 . Substances whose formulas are KOH, Fe(OH)2, NaOH are called:

• A) salts B) acids; B) grounds D) oxides. 10 . Substances whose formulas are NO2, Fe2O3, Na2O are called:

• A) salts B) acids; B) grounds D) oxides.

• 11 . Specify the metals that form alkalis:

• Cu, Fe, Na, K, Zn, Li.

Answers:

• Na, K, Li.