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.

Conditions for the occurrence and flow of chem. reactions

1. Contact of starting substances

2. Heating the starting materials (or their mixture) to a certain temperature

3. In most cases, the use of catalysts

Signs of chemical reactions

1) Color change

2) The appearance of an odor

3) Precipitation

4) Dissolution of the precipitate

5) Gas evolution

6) Release or absorption of energy (heat, energy, light)

Conditions for a complete chemical reaction:
1) Precipitation

2) Gas evolution

3) Formation of a weak electrolyte (water)

By the number of substances and formed substances	By changing the oxidation state of atoms
No change in oxidation state	With a change in oxidation state
COMPOUNDS A + B = AB Several simple or complex substances form one complex	CaO + H 2 O \u003d Ca (OH) 2 PbO + SiO 2 \u003d PbSiO 3	H 2 + Cl 2 \u003d 2HCl 4Fe (OH) 2 + 2H 2 O + O 2 \u003d 4Fe (OH) 3
Decompositions AB = A + B Several simple or complex substances are formed from a complex substance	Cu(OH) 2 \u003d CuO + H 2 O CaCO 3 \u003d CaO + CO 2 NH 4 Cl \u003d NH 3 + HCl	4HNO 3 \u003d 2H 2 O + 4NO 2 + O 2 4KClO 3 \u003d 3KClO 4 + KCl
SUBSTITUTIONS A + BC \u003d AC + B An atom of a simple substance replaces one of the atoms of a complex		CuSO 4 + Fe \u003d FeSO 4 + Cu 2KBr + Cl 2 \u003d 2KCl + Br 2
EXCHANGE AB + CD = AD + CB Compound substances exchange their constituents	NaOH+HCl=NaCl+H 2 O

THERMAL EFFECT.

BY THE PRESENCE OF OTHER SUBSTANCES.

Let's compose the equation of the chemical reaction of the interaction of phosphorus and oxygen

3. According to the law of conservation of mass of substances, the number of atoms before and after the reaction must be the same. This is achieved by placing the coefficients in front of the chemical formulas of the reactants and products of a chemical reaction. We get the final form of the chemical reaction equation. The arrow is replaced by an equal sign. The law of conservation of mass of matter is satisfied: 4P + 5O 2 = 2P 2 O 5

Algorithm

When compiling reaction equations, one must remember the conservation law

masses of substances: all atoms of the molecules of the starting substances must be part of the molecules

reaction products. Not a single atom should disappear or suddenly appear.

Therefore, sometimes, having written all the formulas in the reaction equation, you have to align

the number of atoms in each part of the equation - arrange the coefficients. Here is an example:

There are more oxygen atoms on the left side of the equation than on the right side. Need,

to get so many molecules of copper oxide CuO, so that they have so many

same oxygen atoms, i.e. 2. Therefore, before СuО we set the coefficient 2:

Сu + O 2 \u003d 2CuO

Now the number of copper atoms is not the same. On the left side of the equation before the copper sign

set factor 2:

2Cu + O 2 \u003d 2CuO

As a result, there should be equal atoms of each element in the left and right sides of the equation

One more example:

Al + O 2 \u003d Al 2 O 3

And here the number of atoms of each element is different before and after the reaction. Align

we start with gas - with oxygen molecules:

1) There are 2 oxygen atoms on the left, and 3 on the right. We are looking for the least common multiple of these two

numbers. This is the smallest number that is divisible by both 2 and 3, i.e. 6. Before formulas

oxygen and aluminum oxide Al 2 O 3 we set such coefficients that the total number

there were 6 oxygen atoms in these molecules:

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

2) We count the number of aluminum atoms: on the left there is 1 atom, and on the right in two molecules, 2 each

atom, i.e. 4. Before the sign of aluminum on the left side of the equation, we put the coefficient

4Al + 3O 2 \u003d 2Al 2 O 3

H) Once again we count all the atoms before and after the reaction: 4 aluminum atoms each

and 6 oxygen atoms.

Calculate the amount of copper (I) oxide substance if copper weighing 19.2 g reacts with oxygen.

1. Write down the condition of the problem	Given: m(Cu)=19.2g Find: ν(Cu 2 O)=?
2. Calculate the molar masses of the substances that are discussed in the problem	M(Cu)=64g/mol M(Cu 2 O)=144g/mol
3. Find the amount of substance, the mass of which is given in the condition of the problem
4. Write the reaction equation and arrange the coefficients	4 Cu + O 2 \u003d 2 Cu 2 O
5. Above the formulas of substances, we write the quantities of substances from the condition of the problem, and under the formulas, the stoichiometric coefficients displayed by the reaction equation
6. To calculate the desired amount of a substance, we compose the ratio Answer: ν (Cu 2 O) \u003d 0.15 mol

Lesson topic. Practical work No. 4 "Signs of chemical reactions"

Learning goal:

Improve knowledge about the signs of chemical reactions;

Improve experimental skills:

Determine the purpose of the work;

Use instructions and laboratory equipment;

Conduct reactions;

Observe and record observations;

Write the reaction equations according to the experiment;

Draw conclusions based on observations according to the goal;

Follow the rules of safe behavior Development goal:

Develop independent work and communication skills. Educational goal:

Education of accuracy and consistency in work, respect for school property, one's own health and the health of others.

on student tables.

Reagents: copper(II) oxide, sulfuric acid, chalk, hydrochloric acid, iron(III) chloride, potassium thiocyanate, sodium carbonate, calcium chloride.

Equipment: laboratory tripod, test tubes, spirit lamp, matches

Didactic materials: instruction cards, test and forms for answers to tests.

Epigraph to the lesson"To know the invisible, look carefully at the visible" ancient wisdom

Stage		Activity	Forms of work
teachers	students
Motivation, goal setting		We invite students to write down the topic of the lesson and express ideas about the goals that we have to implement in the lesson. Next, we encourage students to express their own opinion regarding the meaning contained in the epigraph to the lesson, and bring them to the idea that when doing practical work, the skill of observation is very important, since the fundamental part of the experiment is carried out on the basis of observations, namely the conclusion.	They express their own point of view and argue it. Determined in relation to the objectives of the lesson. Express their point of view on the idea of ​​the epigraph.

Updating ZUN	Chemical reactions, recognition chemical chemical equations, coefficient,	We encourage students to take the test. We will organize an active discussion of the results of the test and correction of knowledge. Talking to students about safety at work with equipment and reagents: Work with glass; Rules for working with an alcohol lamp; Handling acids as well as oxides and salts	Perform a test, carry out self-examination and correction of knowledge. Listen and answer the teacher's questions.
Running an experiment	Observation various signs chemical reactions at carrying out	We suggest doing practical work according to the instructions. We monitor the performance of the work, if necessary, help or advise.	Perform practical work, draw up the results of the work, hand over the work to the teacher.
Reflection	Result and activities	We invite students to express their opinion on the results obtained.	Optionally, they answer the question, expressing an opinion about the result achieved and about what contributed to its achievement (or prevented the achievement of more).
Homework	repeat material §24. with. 124-128	The material proposed for homework is necessary to complete the work of preparing a solution with a certain mass fraction of a substance	Ask questions for clarification

Test for updating knowledge and skills

The test can be offered as a control-updating one at this lesson or at the next one. Answers are entered in a special form, the results of the work are collected in a few minutes, and after that we offer students to implement and correct knowledge. The test result is taken into account when marking the work or as a separate type of work with a separate assessment

Test Attention!

Option 1.

one . Chemical phenomena are the transformations of substances when

a) the aggregate state and shape change;

b) the composition of the substance changes;

c) size and mass change;

d) color changes;

2. Chemical phenomena can be conditionally written using

a) physical formulas;

b) mathematical equations;

c) chemical equations;

d) chemical signs

3. Coefficient- This

a) chemical sign;

c) chemical formula:

4. Indicate the signs of a chemical reaction

a) color change:

b) change in shape and size;

c) release of heat (or light);

d) formation of sediment and gas

5. The reaction between a simple and a complex substance is usually a reaction

a) connections; b) substitution;

c) decomposition; d) exchange

Test Attention! There may be several correct answers.

Option-2

1. chemical phenomena- This

a) gas combustion; b) evaporation of water;

c) leaf rot;

d) oil refining;

2. Chemical equations are based on

a) the periodic law;

b) the law of constancy of the composition of J. Proust;

c) the law of conservation of mass of substances;

d) Avogadro's law

3. Index- This

a) chemical sign;

b) the number before the formula or chemical sign;

c) chemical formula;

d) the number next to the chemical sign at the bottom right

4. Precipitation, odor, heat, light, gas, discoloration- This

a) transformation of substances:

b) properties of substances;

c) signs of chemical reactions;

d) physical phenomena:

5. A reaction in which a new, more complex substance is formed from several substances is called a reaction

a) connections;

b) decomposition;

c) exchange;

d) substitution;

Stages of work	Execution experience	Observations	Reaction equations, product names
Interaction of copper(II) oxide with sulfuric acid
Interaction of calcium carbonate (chalk) with hydrochloric acid	CaCO3 and HC1	Observe color, sediment, gas, smell, light or heat.		Indicate the observed signs of this reaction and its type.
Interaction of iron (III) chloride with potassium thiocyanate		Observe color, precipitate, gas. smell, light or heat.		Indicate the observed signs of this reaction and its type.
Interaction carbonate chloride	Na 2C03 and CaCl2	Observe color, precipitate, gas. smell. light or heat.		Indicate the observed signs of this reaction and its type.

BUT. Draw a little man on one of the steps of the ladder - yourself, depending on your active work in the lesson:

https://pandia.ru/text/78/636/images/image003_129.gif" height="38"> 3

B. Check the box next to one of the icons in the first column:

	Everything is clear in class
	There was a feeling that not everything is clear
	Everything was clear, I will be able to conduct experiments myself and observe the signs accompanying them.

AT. Choose the beginning of the sentence you like and complete it
1. Today I learned (a) that I can -----

2. I find it useful

3. I liked it -

4. It was difficult for me

5. Now I would like (a) to know more -------

Homework: review the material §24. with. 124-128

Answer sheet

Class F. I Sum of points Grade

1. Chemical reactions. Signs and conditions of their course. Chemical equations. The law of conservation of mass of substances. Types of chemical reactions.

2. What volume of gas can be obtained by reacting 60 g, 12% potassium carbonate solution with sulfuric acid.

Chemical reaction - the transformation of one or more substances into another.
Types of chemical reactions:

1) Connection reaction- These are reactions as a result of which one more complex is formed from two substances.

2) Decomposition reaction It is a reaction in which several simpler substances are formed from one complex substance.

3) Substitution reaction- these are reactions between simple and complex substances, as a result of which a new simple and a new complex substance is formed.

4) Exchange reaction- these are reactions between two complex substances, as a result of which they exchange their constituent parts.

Reaction conditions:

1) Close contact of substances.
2) Heating
3) Grinding (reactions in solutions are the fastest)
Any chemical reaction can be represented using a chemical equation.

chemical equation- This is a conditional record of a chemical reaction using chemical formulas and coefficients.

The basis of chemical equations is law of conservation of mass of matter : The mass of the substances that entered into the reaction is equal to the mass of the substances resulting from the reaction.
Signs of chemical reactions:

· Color change

· Gas evolution

· Precipitation

· Emission of heat and light

· Odor release

2.

Ticket number 7

1. Basic provisions of T.E.D. - The theory of electrical dissociation.

2. How many grams of magnesium containing 8% impurities can react with 40 g of hydrochloric acid.

Substances soluble in water can dissociate, i.e. break up into oppositely charged ions.
electrical dissociation – the decomposition of the electrolyte into ions during dissolution or melting.
electrolytes – substances whose solutions or melts conduct electric current (acids, salts, alkalis).
They are formed by ionic bonds (salts, alkalis), or covalent, highly polar (acids).
Not electrolytes – substances whose solutions do not conduct electricity (solution of sugar, alcohol, glucose)
During dissociation, electrolytes break down into cations(+) and anions(-)
Ions - charged particles into which atoms turn as a result of giving and taking ē
The chemical properties of electrolyte solutions are determined by the properties of those ions that are formed during dissociation.

Acid - an electrolyte that dissociates into hydrogen cations and an anion of an acid residue.

Sulfuric acid dissociates into 2 H cations with a charge (+) and
anion SO 4 with charge (-)
Foundations - an electrolyte that dissociates into metal cations and hydroxide anions.

salt - electrolyte, which in an aqueous solution dissociates into metal cations and anions of the acid residue.

2.

1. Ion exchange reactions.

Lesson type: acquisition of new knowledge.

Type of lesson: a conversation with a demonstration of experiments.

Goals:

Educational- to repeat the differences between chemical phenomena and physical ones. To form knowledge about the signs and conditions of chemical reactions.

Educational- develop skills based on knowledge of chemistry, pose simple problems, formulate hypotheses., generalize.

Educational - continue the formation of the scientific outlook of students, cultivate a culture of communication through work in pairs "student-student", "student-teacher", as well as observation, attention, inquisitiveness, initiative.

Methods and methodological techniques: Conversation, demonstration of experiments; filling in the table, chemical dictation, independent work with cards.

Equipment and reagents. Laboratory stand with test tubes, an iron spoon for burning substances, a test tube with a gas outlet tube, an alcohol lamp, matches, solutions of iron chloride FeCL 3, potassium thiocyanate KNCS, copper sulfate (copper sulfate) CuSO 4, sodium hydroxide NaOH, sodium carbonate Na 2 CO 3, hydrochloric acid HCL, powder S.

During the classes

Teacher. We study the chapter "Changes that occur with substances" and we know that changes can be physical and chemical. What is the difference between a chemical phenomenon and a physical one?

Student. As a result of a chemical phenomenon, the composition of a substance changes, and as a result of a physical phenomenon, the composition of a substance remains unchanged, and only its state of aggregation or the shape and size of bodies changes.

Teacher. In the same experiment, one can simultaneously observe chemical and physical phenomena. If you flatten a copper wire with a hammer, you get a copper plate. The shape of the wire changes, but its composition remains the same. This is a physical phenomenon. If a copper plate is heated over high heat, the metallic luster will disappear. The surface of the copper plate will be covered with a black coating that can be scraped off with a knife. This means that copper interacts with air and turns into a new substance. This is a chemical phenomenon. A chemical reaction takes place between the metal and oxygen in the air.

Chemical dictation

Option 1

Exercise. Indicate what phenomena (physical or chemical) in question. Explain your answer.

1. Combustion of gasoline in a car engine.

2. Preparation of powder from a piece of chalk.

3. Decay of plant residues.

4. Souring of milk.

5. Rainfall

Option 2

1. Burning coal.

2. Melting snow.

3. Rust formation.

4. Formation of frost on trees.

5. The glow of a tungsten filament in a light bulb.

Evaluation criteria

You can score a maximum of 10 points (1 point for a correctly indicated phenomenon and 1 point for justifying the answer).

Teacher. So, you know that all phenomena are divided into physical and chemical. Unlike physical phenomena, chemical phenomena, or chemical reactions, involve the transformation of one substance into another. These transformations are accompanied by external signs. In order to introduce you to chemical reactions, I will conduct a series of demonstration experiments. You need to identify signs by which you can tell that a chemical reaction has occurred. Pay attention to what conditions are necessary for these chemical reactions to occur.

Demo Experience #1

Teacher. In the first experiment, you need to find out what happens to iron chloride (111) when a solution of potassium thiocyanate KNCS is added to it.

FeCL 3 + KNCS = Fe(NCS) 3 +3 KCL

Student. The reaction is accompanied by a color change

Demo Experience #2

Teacher. Pour 2 ml of copper sulfate into a test tube, add a little sodium hydroxide solution.

CuSO 4 + 2 NaOH \u003d Cu (OH) 2 ↓ + Na 2 SO 4

Student. A blue precipitate Cu (OH) 2↓

Demo Experience #3

Teacher. To the resulting solution of Cu (OH) 2↓ add a solution of acid HCL

Cu (OH) 2↓ + 2 HCL \u003d CuCL 2 +2 HOH

Student. The precipitate dissolves.

Demo Experience #4

Teacher. Pour a solution of hydrochloric acid HCL into a test tube with a solution of sodium carbonate.

Na 2 CO 3 +2 HCL \u003d 2 NaCL + H 2 O + CO 2

Student. Gas is released.

Demo Experience #5

Teacher. Let's set fire to a little sulfur in an iron spoon. Sulfur dioxide is formed - sulfur oxide (4) - SO 2.

S + O 2 \u003d SO 2

Student. Sulfur ignites with a bluish flame, gives off abundant acrid smoke, heat and light are released.

Demonstration experience No. 6

Teacher. The decomposition reaction of potassium permangate is the reaction of obtaining and recognizing oxygen.

Student. Gas is released.

Teacher. This reaction proceeds with constant heating, as soon as it is stopped, the reaction also stops (the tip of the gas outlet tube of the device, where oxygen was received, is lowered into a test tube with water - while heating, oxygen is released, and it can be seen by the bubbles emerging from the tip of the tube, if stop heating - the release of oxygen bubbles also stops).

Demonstration experience No. 7

Teacher. In a test tube with NH 4 CL ammonium chloride, add a little NaOH while heating. Ask one of the students to come up and smell the ammonia that is released. Warn the student about the strong smell!

NH 4 CL + NaOH \u003d NH 3 + HOH + NaCL

Student. A gas with a pungent odor is released.

Students write down signs of chemical reactions in a notebook.

Signs of chemical reactions

Emission (absorption) of heat or light

Color change

Gas evolution

Isolation (dissolution) of the precipitate

Smell change

Using the knowledge of students about chemical reactions, on the basis of the demonstration experiments done, we compile a table of the conditions for the occurrence and occurrence of chemical reactions

Teacher. You have studied the signs of chemical reactions and the conditions for their occurrence. Individual work on cards.

Which of the signs are characteristic of chemical reactions?

A) Precipitation

B) Change in the state of aggregation

B) Gas evolution

D) Grinding of substances

Final part

The teacher sums up the lesson by analyzing the results. Gives grades.

Homework

Give examples of chemical phenomena that occur in the work of your parents, in the household, in nature.

According to O.S. Gabrielyan's textbook "Chemistry - Grade 8" § 26, exercise. 3.6 p.96