Classification of chemical reactions. What are the conditions for the occurrence and course of chemical reactions? Explain with specific examples

The purpose of the lesson: Generalize the idea of ​​a chemical reaction as a process of transformation of one or more initial substances - reagents into substances that differ from them in chemical composition or structure - reaction products. Consider some of the numerous classifications of chemical reactions according to various criteria.

Tasks:

1. Educational- systematize, generalize and deepen students’ knowledge about chemical reactions and their classification, develop independent work skills, the ability to write reaction equations and arrange coefficients, indicate the types of reactions, draw conclusions and generalizations.
2. Developmental- develop speech skills and analytical abilities; development of cognitive abilities, thinking, attention, ability to use studied material to learn new things.
3. Educational- nurturing independence, cooperation, moral qualities - collectivism, the ability to mutual assistance.

Lesson type: learning new material.

Equipment: copper wire, alcohol lamp, zinc, hydrochloric acid, potassium permanganate, stand, test tubes, splinter, cotton wool, barium chloride, sodium sulfate, sulfuric acid, water, chemistry textbook for the 11th grade, workbook, table for filling out the results of laboratory experiments, presentation .

Methods:

• Verbal (story, conversation, explanation);
• Visual (projector);
• Practical (performing experiments).

Form of work: group, frontal.

Lesson plan:

1. Organizing time. (1 min)
2. Updating knowledge: (3 min)

• chemical reaction;
• signs of chemical reactions;
• conditions for chemical reactions.

1. Learning new material:

• classification of chemical reactions (practical work). TB when working with acid and alcohol lamp.

1. Consolidation (doing exercises).
2. Lesson summary.
3. Homework.
4. Reflection.

During the classes

1. Organizational moment. (1 min)

2. Updating knowledge. (3 min)

Without chemistry you are deaf and dumb
And sometimes you can’t take a step,
You can't grow good bread
And you can’t build a good house.
Love chemistry and not be lazy -
So, everything will be clear:
Why does the Primus stove sometimes smoke?
Laundry is drying in the cold.
You will recognize life around you,
Resolve any serious dispute
You can boil eggs on the road without fire
And without matches you can make a fire.

Students are asked questions.

What signs of chemical reactions do you know?

Signs of chemical reactions:

• release or absorption of heat and sometimes release of light;
• color change;
• appearance of odor;
• sediment formation;
• gas release.

What are the conditions for the occurrence and course of chemical reactions?

• grinding and mixing;
• heating.

The teacher thanks the students for their answers.

3. Studying new material.

Guys, life is impossible without chemical reactions. There are a huge number of reactions taking place in the world around us. The teacher asks students to define the term “reaction”, i.e. How do they understand what a reaction is? After the children’s answers, the teacher says that the term “reaction” from Latin means “opposition”, “rebuff”, “response”. (Slide 1)

In order for us to navigate the vast realm of chemical reactions, we need to know the types of chemical reactions. In any science, a classification technique is used that allows dividing the entire set of objects into groups based on common characteristics.

So, the topic of our lesson: “Classification of chemical reactions.” (Slide 2)

And today in the lesson, each of you will learn what types of chemical reactions exist and by what criteria they are classified. The teacher draws the children's attention to the board where the content of the lesson is written.

1. Chemical reactions.
2. Classification of chemical reactions:

• by the number and composition of the initial and formed substances;
• by thermal effect;
• by the presence of a catalyst;
• by state of aggregation;
• towards;
• by change in s.o.

1. Solution of exercises.

Next, the teacher asks students to define the phrase “chemical reaction” (without looking at the textbook). After the proposed options, the teacher asks the children to find the definition in the textbook and read it out. (page 100 of the textbook)

The teacher asks the students a question. What types of chemical reactions do you know, and by what criteria can you classify them? After the students’ answers, the teacher draws the students’ attention to the first type of chemical reactions, based on the number and composition of the starting and resulting substances. (Slide 3)

The class is divided into 4 groups. The first group performs an experiment on a compound reaction, the second group on a substitution reaction, the third group on an exchange reaction, and the fourth group on a decomposition reaction. Before the children begin to carry out the experiments, the teacher asks them to repeat the TB. Three minutes are given to complete the experiments. Each group records the results of their experience in a table prepared by the teacher for each student.

After completing the experiments, a representative from each group comes out and tells what they did and writes down the equation of the chemical reaction on the board, each group gives a definition of the type of reaction using the textbook. Students are shown slides. (Slide 4-7) And the rest of the groups observe, listen and record the results in a table. After this task, the teacher asks students to remember what other types of reactions they know. (Slide 8-9) Examples of these types of chemical reactions are given on the board.

4. Consolidation. (Slide 10-18) Assignments in the form of a test.

5. Lesson summary.

V. Mayakovsky has this philosophical idea: if stars light up in the sky, it means that someone needs it. If chemists study the classification of chemical reactions, then, therefore, someone needs it. And here I have a desire to offer you a short essay in which, using examples, you need to show the meaning of all types of reactions in real life, in its richness and diversity.

6. Homework. Item 11 test execution.(Prepared for each student). (Slide 19)

7. Reflection.

1. What did I learn in class today...?
2. I learned….?

Assignments on the topic “Classification of chemical reactions.”

1. The reaction equation for the production of nitric oxide (ΙΙ) is given: N 2 + O 2 ↔ 2NO – Q

Characterize the reaction according to all the classification criteria you have studied.

2. Match:

3. Give examples of the formation of copper oxide (P) as a result of the reaction:

1. connections,
2. decomposition.

4. Enter the coefficients in the following reaction schemes, determine what type each of them belongs to:

1. Al + Cl 2 → Al 2 O 3
2. CaO + HCl → CaCl 2 + H 2 O
3. NaHCO 3 → Na 2 CO 3 + H 2 O + CO 2
4. Mg + H 2 SO 4 → MgSO 4 + H 2

5. What type of chemical reaction is the formation of carbon dioxide as a result of:

1. interaction of coal with copper oxide;
2. calcination of limestone;
3. burning coal;
4. burning carbon monoxide?

6*. By what external signs can one judge that a chemical reaction has occurred during the interaction of the following pairs of substances:

K 2 S + Pb(NO 3) 2 → FeCl 3 + NaOH → CuO + HNO 3 →

Na 2 CO 3 + HCl → Ca(HCO 3) 2 → t Zn + CuSO 4 →

Write what substances are formed, arrange the coefficients and indicate what type of reaction each of them belongs to.

7*. Give two examples of compound reactions that are accompanied by oxidation - reduction of the substances involved in the reaction.

8*. Give examples of decomposition reactions that are not associated with the oxidation-reduction process.

On “3” - solve tasks 1-5, on “4” and “5” - solve tasks 1-5 and 6-8.

Table of results of laboratory experiments.

Subject:"Classification of chemical reactions."

Laboratory work:"Types of chemical reactions."

List of used literature:

1. Blokhina O.G. I'm going to a chemistry lesson, grades 5-11, M, “First of September”: 2003
2. Gabrielyan O.S. Handbook for a chemistry teacher for grade 11, part 1, M, “Bustard”: 2003.

Conditions for the occurrence and occurrence of reactions. Contact of reacting substances Grinding and mixing Heating.

Picture 19 from the presentation “Examples of physical and chemical phenomena” for physics lessons on the topic “Phenomena”

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Phenomena

“Physical phenomena in everyday life” - Nature. Sunset. Air. Frost. Optical phenomenon. Blue color of the sky. Setting sun. Powerful rain clouds. Physics. Rainbow. Scientific explanation of what was seen. Physics is the science of inquisitive researchers. Cold. The volume increases. Thickness of the cloud formation.

“Physical and chemical phenomena” - What happens if you leave an iron object in a damp place? Grind a piece of sugar in a porcelain mortar. What changes have happened to magnesium tape? Sweet. Sugar crystals. How do physical phenomena differ from chemical phenomena? What can you say about the other properties? Colorless. White. Straight.

“Examples of physical and chemical phenomena” - Physical phenomena. How do physical phenomena differ from chemical phenomena? Water wears away stones. Chemical phenomena. Obtaining distilled water. Phenomena in which the state of aggregation changes. Filtration. Concepts of physical and chemical phenomena. Classification of reactions. Separating funnel.

“Phenomena of living nature” - Eyes are different. Optical phenomena. These faces are familiar to everyone. Interesting. Introduction. A magnetic field. Thermal phenomena. Live direction finders. Electric fish. Physics. Birds always know where to fly. Living power plants. Possibility of use. Living echolocators. Will the wolf catch up with the hare? Mechanical phenomena.

"Ball Lightning" - Ball lightning explodes most of the time. In 30% of cases, lightning calmly fades away. Regular lightning is short-lived. How does it get into closed spaces? Ball lightning poses many mysteries to us. Ordinary lightning is a type of spark electric discharge. Ball lightning does not always end in an explosion.

“Phenomena in Physics” - Physics is one of the main sciences about nature. Example: the ball is on the field. Observations and experiments. Energy is expressed in SI units in joules. In physics, special words or terms are used to denote physical concepts. Every body has shape and volume. Pressure. However, a button with a sharper end will go into the wood more easily.

There are 11 presentations in total

By the end of the 19th century. New questions arise, the answers to which could not be given by classics, marginalism and the like. The questions were: 1) Monopoly 2) Economy. crises 3) Unemployment The cause of economic failure. science was largely due to the fact that classical. the school was distinguished by a certain abstractness, isolation from reality, and for this feature the classic. opponents began to pay attention to the school from the beginning of the 19th century. and Sismondi was one of the first to point this out. Subsequent criticism of the classical school was continued by the historical school, which showed that economics. science cannot be uniform for all countries; on the other hand, it cannot be considered that ET is divorced from other disciplines. He, as a kind of continuation of the historical school, continued his criticism of the classics, and also developed the idea that the state should regulate the economy. processes. Reasons for the emergence of institutionalism The reasons for the emergence of institutionalism include the transition of capitalism to the monopoly stage, which was accompanied by significant centralization of production and capital, which gave rise to social contradictions in society. The concept of institutionalism Institutionalism (from Latin institutio - “custom, instruction”) is a direction of economic thought that was formed in the 20-30s of the 20th century to study the totality of socio-economic factors (institutions) over time, as well as to study social control society over the economy. Institutions are the primary elements of the driving force of society, considered in historical development. Among the institutions are: public institutions - family, state, legal norms, monopoly, competition, etc.; concepts of social psychology - property, credit, income, tax, customs, traditions, etc. Characteristic features of institutionalism: the basis of analysis is the method of describing economic phenomena; the object of analysis is the evolution of social psychology; the driving force of the economy, along with material factors, are moral, ethical and legal elements in historical development; interpretation of socio-economic phenomena from the point of view of social psychology; dissatisfaction with the use of abstractions inherent in neoclassicism; the desire to integrate economic science with social sciences; the need for detailed quantitative research of phenomena; protection of the implementation of the state's antimonopoly policy.

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Let's consider how in chemistry lessons in grades VII-VIII one should develop knowledge about the conditions for the occurrence and course of a chemical reaction.

In the first lessons, it is enough if students learn that under the same conditions one substance undergoes a chemical transformation, and another does not (heating stearin and sugar), that under some conditions only a physical change occurs with a substance, and under others a chemical one (dissolving and heating sugar).

After familiarization with the signs of a chemical reaction, the first generalization of knowledge about the conditions of chemical interaction is carried out, organized as follows. Students are asked to answer the question: What conditions are needed for: a) sugar to char, b) magnesium to catch fire, c) a copper plate to become covered with a black coating? In all these cases they call the same condition - heating of substances. Discussing the answers, the teacher notes that for Magnesium to burn and the copper plate to blacken, heating alone is not enough; contact of the metals with oxygen in the air is necessary. To confirm, he shows the glow of a piece of shiny thin sheet copper, folded into an envelope with the edges pressed tightly together, or thick copper wires twisted together. After cooling, it turns out that the copper on the outside turned black, but on the inside remained shiny, since oxygen molecules did not penetrate here.

The teacher demonstrates a solution of copper sulfate in a glass cylinder, onto which a diluted solution of ammonium hydroxide was carefully poured on top. He notes the appearance of a bright blue color only in the middle part of the vessel and says that the chemical reaction, starting at the place where the liquids come into contact with each other, can occur throughout the entire volume only if stirring is applied. Students develop their first ideas about such conditions of chemical interaction as the contact of reacting substances and their mixing.

In conclusion, it is noted that the most important conditions for a chemical reaction are: 1) the presence of substances that can undergo chemical transformations, 2) contact and mixing of substances (if the reaction occurs between two substances), 3) heating.

To test and consolidate knowledge, use the following questions and tasks:

1. Name the conditions necessary for chemical reactions. Give examples. What is the significance of knowledge of these conditions for practice?
2. What conditions were necessary for: a) copper to become covered with a black coating, b) lime water to become cloudy?
3. What conditions do we create for a chemical reaction to occur when we light an alcohol lamp or a gas burner? Which of these conditions do we violate when we extinguish the flame?

When studying the next topic - “Initial information about the structure and composition of substances” - the teacher pays attention to the conditions of those transformations that are used to form the concept of decomposition reactions and combination reactions. Emphasizes that the decomposition of mercury oxide and basic copper carbonate requires constant heating, and the decomposition of water requires the action of electric current. The combination of sulfur with iron begins only when heated, and then, since heat is released during this reaction, further heating of the mixture is no longer necessary.

Students should learn that not all decomposition reactions involve the absorption of heat and not every combination of substances is accompanied by its release. The teacher demonstrates his experience: he heats a test tube with ammonium dichromate only until the reaction begins, which continues after heating stops. Warming up a substance and throwing out hot particles from a test tube shows that the reaction proceeds with the release of heat.

Then an example of a compound reaction that occurs with the absorption of heat is given: the combination of nitrogen with oxygen occurs at temperatures above 1200 ° C and requires constant heating.

Further development and consolidation of knowledge about the conditions of chemical reactions occurs in the topic "Oxygen. Air."

After studying the chemical properties of oxygen, students are asked questions:

1. What conditions are necessary for burning charcoal; sulfur, phosphorus and magnesium in oxygen and air? Why is it enough to heat these substances only before the reaction begins?
2. Why is a piece of cork attached to the tip of the feather before burning a steel feather in oxygen? Is heat released when iron reacts with oxygen? Why do you think so?
3. What are the combustion conditions and how do we create them when we light gas on a gas stove?

Once students have studied the composition of air, they can be given the following tasks and questions:

1. Compare the conditions: a) the formation of red mercuric oxide powder in Lavoisier’s experiment and b) the decomposition of mercury oxide. What are the similarities and differences between these conditions?
2. Why does the formation of mercury oxide stop when mercury is heated for a long time in a closed vessel with air? What condition of mercury oxidation is violated?
3. A burning candle was placed in a large jar of air, then the jar was sealed with a stopper. The candle burned for a while and then went out. Why did the burning stop? Which condition for the interaction of substances was violated?

In the topic "Hydrogen" it is useful to understand why in the Kipp apparatus, when the tap is closed, the reaction stops, and what conditions for the reaction are violated.

The topic "Water. Diseases" examines the chemical properties of water and studies the reaction of water with metals. At the same time, experiments are carried out that make it possible to note that various metals react with water under different temperature conditions. In the same topic, it is desirable to compare the conditions for the decomposition of water and its synthesis, to draw attention to the fact that the decomposition of water occurs under the continuous action of an electric current, and an electric spark is sufficient to explode a mixture of hydrogen and oxygen in the eudiometer. After this, students should be asked which of the reactions under consideration involves the release and which involves the absorption of energy.

In grade VIII, when studying exchange reactions between two salts, a salt and a base, it is necessary to show what the most important conditions for these reactions are: the solubility of the starting substances in water and the presence of water.

At the end of studying the topic “The Most Important Classes of Inorganic Compounds,” students compile tables that include a number of examples of studied chemical transformations of water-soluble and water-insoluble inorganic substances, as well as information about the types and conditions of these transformations. An example of one such table is shown below.

When discussing the contents of the tables, they first of all emphasize that there is no definite correspondence between the type of chemical interaction and the reaction conditions: some substitution reactions occur without heating, while others (between copper oxide and hydrogen) occur with heating, the same can be said about exchange reactions. Nevertheless, some connections between the types of reactions, the participation of soluble and insoluble substances in them and the conditions can be noticed.

If a substitution reaction involves a complex substance (acid, salt) soluble in water, then the reaction is carried out in its solution without heating. If the complex substance is insoluble in water, then heating is required.

An exchange reaction between TWO salts, a salt and a base, occurs without heating only if these substances are soluble. Water-insoluble oxides can also participate in the exchange reaction between an oxide and an acid, but in this case heating is required.

The development of knowledge about the conditions for the occurrence and course of the reaction continues in the topics: “Carbon and its compounds”, “Metals”, “Chemistry and its importance in the national economy”.

While studying allotropic modifications of carbon, the teacher introduces students to the conditions for obtaining artificial diamonds.

The systematic development of knowledge about the conditions for the occurrence and course of chemical reactions in grades VII and VIII allows students to pose questions that clarify the conditions necessary for the ignition of substances and the continuation of combustion. Experiments are demonstrated, for example, the flame of alcohol is extinguished by closing the crucible with a lid, and the flame of turpentine is extinguished by immersing the crucible in cold water.

In the topic “Metals”, much attention should be paid to clarifying the conditions for rusting of iron and ways to protect it from rusting *.

* (P. A. Gloriozov, E. P. Kleshcheva, L. A. Korobeynikova. T. 3. Savich. Methods of teaching chemistry at an eight-year school. M., "Enlightenment", 1966.)

Finally, in the topic “Chemistry and its importance in the national economy”, discussing the role of chemistry in the national economy of the USSR and in nature conservation, it is very useful to once again point out the great importance of the knowledge accumulated in science about the conditions of chemical reactions and their successful application at present in various areas of the national economy in everyday life.

In industry, conditions are selected so that the necessary reactions are carried out and harmful ones are slowed down.

TYPES OF CHEMICAL REACTIONS

Table 12 shows the main types of chemical reactions according to the number of particles involved in them. Drawings and equations of reactions often described in textbooks are given. decomposition, connections, substitution And exchange.

At the top of the table are presented decomposition reactions water and sodium bicarbonate. Shown is a device for passing direct electric current through water. The cathode and anode are metal plates immersed in water and connected to a source of electric current. Due to the fact that pure water practically does not conduct electric current, a small amount of soda (Na 2 CO 3) or sulfuric acid (H 2 SO 4) is added to it. When current passes through both electrodes, gas bubbles are released. In the tube where hydrogen is collected, the volume turns out to be twice as large as in the tube where oxygen is collected (its presence can be verified with the help of a smoldering splinter). The model diagram demonstrates the reaction of water decomposition. Chemical (covalent) bonds between atoms in water molecules are destroyed, and molecules of hydrogen and oxygen are formed from the released atoms.

Model diagram connection reactions metallic iron and molecular sulfur S 8 shows that as a result of rearrangement of atoms during the reaction, iron sulfide is formed. In this case, the chemical bonds in the iron crystal (metallic bond) and the sulfur molecule (covalent bond) are destroyed, and the released atoms are combined to form ionic bonds to form a salt crystal.

Another reaction of the compound is the slaking of lime with CaO with water to form calcium hydroxide. At the same time, the burnt (quicklime) lime begins to heat up and loose slaked lime powder is formed.

TO substitution reactions refers to the interaction of a metal with an acid or salt. When a sufficiently active metal is immersed in a strong (but not nitric) acid, hydrogen bubbles are released. The more active metal displaces the less active metal from the solution of its salt.

Typical exchange reactions is a neutralization reaction and a reaction between solutions of two salts. The figure shows the preparation of barium sulfate precipitate. The progress of the neutralization reaction is monitored using the phenolphthalein indicator (the crimson color disappears).

Table 12

Types of chemical reactions

AIR. OXYGEN. COMBUSTION

Oxygen is the most abundant chemical element on Earth. Its content in the earth's crust and hydrosphere is presented in Table 2 "Occurrence of chemical elements." Oxygen accounts for approximately half (47%) of the mass of the lithosphere. It is the predominant chemical element of the hydrosphere. In the earth's crust, oxygen is present only in bound form (oxides, salts). The hydrosphere is also represented mainly by bound oxygen (part of the molecular oxygen is dissolved in water).

The atmosphere contains 20.9% free oxygen by volume. Air is a complex mixture of gases. Dry air consists of 99.9% nitrogen (78.1%), oxygen (20.9%) and argon (0.9%). The content of these gases in the air is almost constant. The composition of dry atmospheric air also includes carbon dioxide, neon, helium, methane, krypton, hydrogen, nitric oxide (I) (dianitrogen oxide, nitrogen hemioxide - N 2 O), ozone, sulfur dioxide, carbon monoxide, xenon, nitric oxide ( IV) (nitrogen dioxide – NO 2).

The composition of air was determined by the French chemist Antoine Laurent Lavoisier at the end of the 18th century (Table 13). He proved the oxygen content in the air and called it “life air.” To do this, he heated mercury on a stove in a glass retort, the thin part of which was placed under a glass cap placed in a water bath. The air under the hood turned out to be closed. When heated, mercury combined with oxygen, turning into red mercuric oxide. The “air” remaining in the glass bell after heating the mercury did not contain oxygen. The mouse, placed under the hood, was suffocating. Having calcined the mercury oxide, Lavoisier again isolated oxygen from it and again obtained pure mercury.

The oxygen content in the atmosphere began to increase noticeably about 2 billion years ago. As a result of the reaction photosynthesis a certain volume of carbon dioxide was absorbed and the same volume of oxygen was released. The figure in the table schematically shows the formation of oxygen during photosynthesis. During photosynthesis in the leaves of green plants containing chlorophyll, when solar energy is absorbed, water and carbon dioxide are converted into carbohydrates(sugar) and oxygen. The reaction of the formation of glucose and oxygen in green plants can be written as follows:

6H 2 O + 6CO 2 = C 6 H 12 O 6 + 6O 2.

The resulting glucose becomes insoluble in water starch, which accumulates in plants.

Table 13

Air. Oxygen. Combustion

Photosynthesis is a complex chemical process that includes several stages: the absorption and transport of solar energy, the use of sunlight energy to initiate photochemical redox reactions, the reduction of carbon dioxide and the formation of carbohydrates.

Sunlight is electromagnetic radiation of different wavelengths. In the chlorophyll molecule, when visible light (red and violet) is absorbed, electrons transition from one energy state to another. Only a small portion of solar energy (0.03%) reaching the Earth's surface is consumed for photosynthesis.

All carbon dioxide on Earth goes through the photosynthesis cycle on average in 300 years, oxygen in 2000 years, and ocean water in 2 million years. Currently, a constant oxygen content has been established in the atmosphere. It is almost completely spent on respiration, combustion and decay of organic substances.

Oxygen is one of the most active substances. Processes involving oxygen are called oxidation reactions. These include combustion, breathing, rotting and many others. The table shows the combustion of oil, which occurs with the release of heat and light.

Combustion reactions can bring not only benefits, but also harm. Combustion can be stopped by cutting off the access of air (oxidizer) to the burning object using foam, sand or a blanket.

Foam fire extinguishers are filled with a concentrated solution of baking soda. When it comes into contact with concentrated sulfuric acid, located in a glass ampoule at the top of the fire extinguisher, a foam of carbon dioxide is formed. To activate the fire extinguisher, turn it over and hit the floor with a metal pin. In this case, the ampoule with sulfuric acid breaks and the carbon dioxide formed as a result of the reaction of the acid with sodium bicarbonate foams the liquid and throws it out of the fire extinguisher in a strong stream. Foamy liquid and carbon dioxide, enveloping a burning object, pushes away the air and extinguishes the flame.

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