I. New material

From the course of natural history and physics, you know that various changes occur with bodies and substances.

Before starting to study the topic of the lesson, I suggest that you complete the following task, take your time with the answers, complete the task to the end.

Exercise:

Look at the pictures carefully and try to answer the following questions:

1. Where can one observe the phenomena presented in the figures and pictures?

№1

№2

№3

№4


№5

№6

2. Give a name to each phenomenon. What substances are involved in the presented phenomena? What happens to each substance in the occurring phenomenon? Write in your workbooks and complete the following table:

№, Name of the phenomenon

Substance involved in the phenomenon

Changes in matter

№1,..



…



№6,..



3. In what phenomena are new substances formed?

4. How and on what grounds can the presented phenomena be divided?

Physical and chemical phenomena

By conducting experiments and observations, we are convinced that substances can change.

Changes in substances that do not lead to the formation of new substances (with different properties) are called physical phenomena.


1. Water when heated, it can turn into steam, and when cooled - into the ice .

2.Length of copper wires changes in summer and winter: increases with heating and decreases with cooling.

3.Volume the air in the balloon increases in a warm room.

Substances changed, but water remained water, copper remained copper, and air remained air.

New substances, despite their changes, were not formed.

WE ANALYZE EXPERIENCE

1. Close the test tube with a stopper with a tube inserted into it

2. Dip the end of the tube into a glass of water. Heat the test tube by hand. The volume of air in it increases, and part of the air from the test tube goes into a glass of water (air bubbles are released).

3. As the tube cools, the air volume decreases and water enters the tube.

Conclusion. Air volume changes are a physical phenomenon.

Chemical phenomenon (reaction) - a phenomenon in which new substances are formed.

How can you tell what happenedchemical reaction ? Precipitation occurs during some chemical reactions. Other signs are a change in the color of the original substance, a change in its taste, the release of gas, the release or absorption of heat and light.

See the table for examples of such reactions.

Signs of chemical reactions

Changing the color of the original substance

Changing the taste of the original substance

Precipitation

Gas evolution

The appearance of an odor

REACTION

SIGN


COLOR CHANGE


TASTE CHANGE


GAS RELEASE

Various chemical reactions are constantly taking place in animate and inanimate nature. Our organism is also a real factory of chemical transformations of some substances into others.

Let's observe some chemical reactions.

Experiments with fire cannot be carried out on your own !!!

Experience 1

Hold over the fire a piece of white bread containing organic matter.

Watching:

1. Charring, that is, discoloration;

2. The appearance of a smell.

Conclusion . A chemical phenomenon occurred (a new substance was formed - coal)

Experience 2

Let's cook glass of starch. Add some water, mix. Then drip iodine solution.

Watching:

1. Sign of reaction: discoloration (blue starch)

Conclusion. A chemical reaction has taken place. The starch has been transformed into another substance.

Experience 3

1. Dilute a small amount of baking soda in a glass.

2. Add a few drops of vinegar there (you can take lemon juice or a solution of citric acid).
Watching:
1. Isolation of gas bubbles.

Conclusion. Gas evolution is one of the signs of a chemical reaction.

Some chemical reactions are accompanied by the release of heat.

Summing up

1. Substances can participate in physical and chemical phenomena

2. Comparative characteristics of physical and chemical phenomena are represented by the following interactive animation

3. The difference between physical and chemical phenomena

During physical phenomena, the molecules of a substance are not destroyed, the substance is preserved.

In chemical phenomena, the molecules of a substance break up into atoms, molecules of a new substance are formed from the atoms.

signschemicalreactions

Color change


Precipitation or dissolution of the precipitate

Think, answer, do...

Phenomena Result signs Examples
Physical there is no transformation of one substance into another change in the state of matter
  • water evaporation
  • melting ice
  • dissolving salt in water and releasing it from the solution
change in the shape of an object that is made of a given substance
  • grinding sugar into powdered sugar
  • glass melting
  • paraffin melting
  • making aluminum foil from aluminum sheet
Chemical new substances are formed from these substances release of heat, light
  • fuel combustion
  • ignition of a match
discoloration
  • bleaching fabrics with bleach
  • adding lemon to tea
the appearance of an odor
  • rotten eggs
  • sugar decomposition
  • burning food
sedimentation
  • turbidity of lime water
  • scale formation in the kettle
outgassing
  • extinguishing soda with acetic acid

Phenomena Examples

The significance of these phenomena in human life and activity

1. Physical phenomena

1) water evaporation, water vapor condensation, rainfall

water cycle in nature

2) giving a certain shape to various materials in industrial production

obtaining a variety of items

2. Chemical phenomena

1) biochemical processes

occur in plants, animals, humans

2) fuel combustion

obtaining thermal energy

3) iron rusting

negative value - destruction of iron products

4) interaction of detergents with various types of contaminants

used in everyday life

5) sour milk

obtaining dairy products

Conditions for the occurrence and course of chemical reactions

1. Grinding and mixing of substances:

a) in order for a chemical reaction to start, sometimes contact of the reactants is sufficient (for example, the interaction of iron with moist air);

b) the more crushed the substances, the greater the surface of their contact with each other, the faster the reaction between them (for example, a lump of sugar is difficult to ignite, and finely ground and atomized sugar in the air burns instantly, with an explosion);

c) facilitates the conduct of chemical reactions between substances, their preliminary dissolution.

2. Heating substances to a certain temperature. Heating affects the occurrence and course of chemical reactions in different ways:

a) in some cases, heating is required only for the reaction to occur, and then the reaction proceeds by itself (for example, burning wood and other combustible substances);

b) for other reactions, continuous heating is required, heating stops - the chemical reaction also stops (for example, the decomposition of sugar).

1. Does not apply to physical phenomena

1) freezing water

2) aluminum melting

3) burning gasoline

4) water evaporation

2. Does not apply to chemical phenomena

1) iron rusting

2) burning food

3) burning gasoline

4) water evaporation

Physical changes are not associated with chemical reactions and the creation of new products, such as the melting of ice. As a rule, such transformations are reversible. In addition to examples of physical phenomena, in nature and in everyday life there are also chemical transformations in which new products are formed. Such chemical phenomena (examples will be discussed in the article) are irreversible.

Chemical changes

Chemical change can be thought of as any phenomenon that allows scientists to measure chemical properties. Many reactions are also examples of chemical phenomena. While it's not always easy to tell that a chemical change has occurred, there are some telltale signs. What are chemical phenomena? Let's give examples. This may be a change in the color of the substance, temperature, the formation of bubbles or (in liquids) precipitation. The following examples of chemical phenomena in life can be given:

  1. Rust on iron.
  2. Burning wood.
  3. Metabolism of food in the body.
  4. Mixing acid and alkali.
  5. Cooking an egg.
  6. Digestion of sugar by amylase in saliva.
  7. Mixing baking soda and vinegar in baking to produce carbon dioxide gas.
  8. Baking a pie.
  9. Metal galvanization.
  10. Batteries.
  11. Fireworks explosion.
  12. Rotting bananas.
  13. Formation of lactic acid products.

And this is not the whole list. You can consider some of these points in more detail.

Outdoor fire using wood

Fire - this is also an example of a chemical phenomenon. This is the rapid oxidation of a material in an exothermic chemical combustion process, releasing heat, light, and various reaction products. The fire is hot because the weak double bond in molecular oxygen O 2 is converted to stronger bonds in the combustion products of carbon dioxide and water. A lot of energy is released (418 kJ per 32 g O 2); the binding energies of the fuel play only a minor role here. At a certain point in the combustion reaction, called the flash point, a flame is formed.

This is the visible part of the fire, which consists mainly of carbon dioxide, water vapor, oxygen and nitrogen. If the temperature is high enough, the gases can become ionized to form a plasma. Depending on what substances are ignited and what impurities are supplied from outside, the color of the flame and the intensity of the fire will be different. Fire in its most common form can start a fire that can cause physical damage when burned. Fire is an important process that affects ecological systems around the world. The positive effects of fire include stimulating growth and maintaining various ecological systems.

Rust

Just like fire, the rusting process is also an oxidative process. Just not as fast. Rust is iron oxide, usually a red oxide, formed by the redox reaction of iron and oxygen in the presence of water or air. Several forms of rust differ both visually and spectroscopy and form under different circumstances. Given enough time, oxygen, and water, any mass of iron eventually completely turns to rust and decomposes. The surface part of it is flaky and loose, and it does not protect the underlying iron, in contrast to the formation of patina on copper surfaces.

An example of a chemical phenomenon, rusting is a general term for the corrosion of iron and its alloys such as steel. Many other metals undergo similar corrosion, but the resulting oxides are not usually referred to as rust. Other forms of this reaction exist as a result of the reaction between iron and chloride in an oxygen-deprived environment. An example is rebar used in underwater concrete pillars, which generates green rust.

Crystallization

Another example of a chemical phenomenon is crystal growth. This is a process in which a pre-existing crystal becomes larger as the number of molecules or ions increases in their positions in the crystal lattice. A crystal is defined as atoms, molecules, or ions arranged in an ordered, repeating pattern, a crystal lattice that extends through all three spatial dimensions. Thus, the growth of crystals differs from the growth of a liquid drop in that during growth, molecules or ions must fall into the correct positions of the lattice in order for an ordered crystal to grow.

When molecules or ions fall into a position different from the positions in the ideal crystal lattice, crystal defects are formed. As a rule, molecules or ions in the crystal lattice are trapped in the sense that they cannot move from their positions, and therefore the growth of crystals is often irreversible, since when the molecules or ions fall into place in the growing lattice, they are fixed in it. Crystallization is a common process in both industry and the natural world, and crystallization is generally understood to consist of two processes. If a crystal did not previously exist, then a new crystal must be nucleated, and then it must undergo growth.

Chemical origin of life

The chemical origin of life refers to the conditions that could have existed and therefore contributed to the appearance of the first duplicated life forms.

The main example of chemical phenomena in nature is life itself. It is believed that a combination of physical and chemical reactions could lead to the appearance of the first molecules, which, being reproduced, led to the appearance of life on the planet.

For the last 200 years of mankind studied the properties of substances better than in the entire history of the development of chemistry. Naturally, the number of substances is also growing rapidly, this is due primarily to the development of various methods for obtaining substances.

In everyday life, we come across many substances. Among them are water, iron, aluminum, plastic, soda, salt and many others. Substances that exist in nature, such as oxygen and nitrogen contained in the air, substances dissolved in water, and having a natural origin, are called natural substances. Aluminum, zinc, acetone, lime, soap, aspirin, polyethylene and many other substances do not exist in nature.

They are obtained in the laboratory and produced by the industry. Artificial substances do not occur in nature, they are created from natural substances. Some substances that exist in nature can also be obtained in a chemical laboratory.

So, when potassium permanganate is heated, oxygen is released, and when chalk is heated - carbon dioxide. Scientists have learned how to turn graphite into diamond, grow crystals of ruby, sapphire and malachite. So, along with substances of natural origin, there is a huge variety of artificially created substances that are not found in nature.

Substances that are not found in nature are produced at various enterprises: factories, plants, combines, etc.

In the conditions of the exhaustion of the natural resources of our planet, chemists now face an important task: to develop and implement methods by which it is possible to artificially, in a laboratory or industrial production, obtain substances that are analogues of natural substances. For example, reserves of fossil fuels in nature are running out.

There may come a time when oil and natural gas run out. Already, new types of fuel are being developed that would be just as efficient, but would not pollute the environment. To date, mankind has learned to artificially obtain various precious stones, such as diamonds, emeralds, beryls.

Aggregate state of matter

Substances can exist in several states of aggregation, three of which you know: solid, liquid, gaseous. For example, water in nature exists in all three states of aggregation: solid (in the form of ice and snow), liquid (liquid water) and gaseous (water vapor). Substances are known that cannot exist under normal conditions in all three states of aggregation. An example of this is carbon dioxide. At room temperature, it is an odorless and colorless gas. At -79°С this substance "freezes" and passes into a solid state of aggregation. The household (trivial) name for such a substance is "dry ice". This name is given to this substance due to the fact that "dry ice" turns into carbon dioxide without melting, that is, without transitioning to a liquid state of aggregation, which is present, for example, in water.

Thus, an important conclusion can be drawn. When a substance passes from one state of aggregation to another, it does not change into other substances. The very process of some change, transformation, is called a phenomenon.

physical phenomena. Physical properties of substances.

Phenomena in which substances change the state of aggregation, but do not turn into other substances, are called physical. Each individual substance has certain properties. The properties of substances can be different or similar to each other. Each substance is described using a set of physical and chemical properties. Let's take water as an example. Water freezes and turns into ice at a temperature of 0°C, and boils and turns into steam at a temperature of +100°C. These phenomena are physical, since water has not turned into other substances, only a change in the state of aggregation occurs. These freezing and boiling points are physical properties specific to water.

The properties of substances that are determined by measurements or visually in the absence of the transformation of some substances into others are called physical

The evaporation of alcohol, like the evaporation of water- physical phenomena, substances at the same time change the state of aggregation. After the experiment, you can make sure that alcohol evaporates faster than water - these are the physical properties of these substances.

The main physical properties of substances include the following: state of aggregation, color, odor, solubility in water, density, boiling point, melting point, thermal conductivity, electrical conductivity. Such physical properties as color, smell, taste, shape of crystals can be determined visually, using the senses, and density, electrical conductivity, melting and boiling points are determined by measurement. Information about the physical properties of many substances is collected in special literature, for example, in reference books. The physical properties of a substance depend on its state of aggregation. For example, the density of ice, water and water vapor is different.

Gaseous oxygen is colorless, and liquid oxygen is blue. Knowledge of physical properties helps to "recognize" a lot of substances. For example, copper- the only red metal. Only table salt has a salty taste. iodine- an almost black solid that turns into a purple vapor when heated. In most cases, to define a substance, several of its properties must be considered. As an example, we characterize the physical properties of water:

  • color - colorless (in a small volume)
  • odor - odorless
  • state of aggregation - under normal conditions, liquid
  • density - 1 g / ml,
  • boiling point – +100°С
  • melting point - 0°С
  • thermal conductivity - low
  • electrical conductivity - pure water does not conduct electricity

Crystalline and amorphous substances

When describing the physical properties of solids, it is customary to describe the structure of the substance. If you look at a sample of table salt under a magnifying glass, you will notice that the salt consists of many tiny crystals. Very large crystals can also be found in salt deposits. Crystals are solid bodies that have the shape of regular polyhedra. Crystals can be of various shapes and sizes. Crystals of certain substances, such as table salt – fragile, easy to break. There are crystals quite hard. For example, one of the hardest minerals is diamond. If you look at salt crystals under a microscope, you will notice that they all have a similar structure. If we consider, for example, glass particles, then they will all have a different structure - such substances are called amorphous. Amorphous substances include glass, starch, amber, beeswax. Amorphous substances - substances that do not have a crystalline structure

chemical phenomena. Chemical reaction.

If, in physical phenomena, substances, as a rule, only change the state of aggregation, then in chemical phenomena, some substances are transformed into other substances. Here are some simple examples: the burning of a match is accompanied by charring of wood and the release of gaseous substances, that is, an irreversible transformation of wood into other substances occurs. Another example: over time, bronze sculptures become covered with a green coating. This is because bronze contains copper. This metal slowly interacts with oxygen, carbon dioxide and air moisture, as a result, new green substances are formed on the surface of the sculpture. Chemical phenomena - the phenomena of the transformation of one substance into another The process of interaction of substances with the formation of new substances is called a chemical reaction. Chemical reactions take place all around us. Chemical reactions take place in ourselves. In our body, transformations of many substances are constantly taking place, substances react with each other, forming reaction products. Thus, in a chemical reaction there are always reacting substances, and substances formed as a result of the reaction.

  • Chemical reaction- the process of interaction of substances, as a result of which new substances with new properties are formed
  • Reagents- substances that enter into a chemical reaction
  • Products- substances formed as a result of a chemical reaction

A chemical reaction is represented in general terms by a reaction scheme REAGENTS -> PRODUCTS

  • reagents– initial substances taken for the reaction;
  • products- new substances formed as a result of the reaction.

Any chemical phenomena (reactions) are accompanied by certain signs, with the help of which chemical phenomena can be distinguished from physical ones. Such signs include a change in the color of substances, the release of gas, the formation of a precipitate, the release of heat, and the emission of light.

Many chemical reactions are accompanied by the release of energy in the form of heat and light. As a rule, such phenomena are accompanied by combustion reactions. In combustion reactions in air, substances react with oxygen contained in the air. So, for example, magnesium metal flares up and burns in air with a bright blinding flame. That is why magnesium flash was used to create photographs in the first half of the twentieth century. In some cases, it is possible to release energy in the form of light, but without the release of heat. One of the species of Pacific plankton is able to emit a bright blue light, clearly visible in the dark. The release of energy in the form of light is the result of a chemical reaction that occurs in the organisms of this type of plankton.

Summary of the article:

  • There are two large groups of substances: substances of natural and artificial origin.
  • Under normal conditions, substances can be in three states of aggregation
  • The properties of substances that are determined by measurements or visually in the absence of the transformation of some substances into others are called physical
  • Crystals are solid bodies that have the shape of regular polyhedra.
  • Amorphous substances - substances that do not have a crystalline structure
  • Chemical phenomena - the phenomena of the transformation of one substance into another
  • Reagents are substances that enter into a chemical reaction.
  • Products - substances formed as a result of a chemical reaction
  • Chemical reactions may be accompanied by the release of gas, sediment, heat, light; color change of substances
  • Combustion is a complex physical and chemical process of transformation of starting materials into combustion products during a chemical reaction, accompanied by intense release of heat and light (flame)

Attention! The site administration site is not responsible for the content of methodological developments, as well as for the compliance of the development of the Federal State Educational Standard.

Class: 8.

Course name: Chemistry .

The purpose of the lesson: formation of students' ideas about physical and chemical phenomena, signs and conditions of chemical reactions based on the integration of knowledge in physics, biology, life safety.

Lesson objectives:

Educational:

  • to form the ability to observe phenomena, recognize them and draw conclusions based on observations;
  • to form the ability to conduct an experiment in order to respect health;
  • to form the ability to explain the significance of phenomena in the life of nature and man;
  • to study the concepts of "physical phenomena", "chemical phenomena", "signs of chemical reactions", "reaction conditions";
  • show the practical significance of knowledge about chemical phenomena, using interdisciplinary connections.

Educational:

  • to cultivate a belief in the cognizability of the chemical component of the picture of the world;
  • nurture respect for your health.

Developing:

  • develop cognitive and communicative activity,
  • to develop the ability to observe the world around us, to think about its essence, the possibility of influencing the processes taking place around us.

During the lesson, the following are formed and developed: competencies:

  • value-semantic (the student's ability to see and understand the world around him);
  • educational and cognitive (skills of students in the field of independent cognitive activity - the organization of goal-setting, planning, analysis, reflection, self-assessment);
  • informational (the ability to independently search, analyze, select the necessary information, transform it, etc.)
  • communicative (skills of working in a group, ways of interacting with other people).

Lesson type: learning new material.

Methods:

  • reproductive,
  • partial search,
  • search.

Equipment and reagents:

  • on the demonstration table: 4 glasses, test tube, matches, candle, torch, NaHCO 3 , CH 3 COOH, H 2 O, NaOH, F.F.
  • on the tables of students: trays for experiments, glass slide, wooden stick, crucible tongs, mortar, pestle, torch, matches, paraffin, CaCO 3 , HCI, NaHCO 3 , CaCl 2 .

Lesson structure:

  1. Motivation.
  2. Goal setting. Updating the knowledge of students from the course of biology, physics and life safety. Creation of a problem situation.
  3. Experiment as a way of knowing.
  4. Analysis and generalization of the obtained results. Conclusion (definition of a chemical reaction). Expansion of information about the new concept (signs of chemical reactions, conditions for their occurrence).
  5. Consolidation. Reflection.
  6. Estimates. Homework.
  7. Summing up the lesson.

During the classes

Tell me and I will forget.
Show me and I will remember.
Let me do it myself and I'll learn.

(Chinese wisdom)

1. Motivation

Teacher: Hello, today our lesson will start with a demo. Your attention is invited to observe 2 experiments ( show jars):

1 experience: NaHCO 3 + CH 3 COOH → CH 3 COONa + H 2 O + CO 2 (burning torch)

2 experience: NaHCO 3 + H 2 O →

Question: What did you observe during the reactions?

Answer: 1 experience - a gas is released that does not support combustion, because the burning torch goes out. 2 experiment - dissolving baking soda in water.

Question: What conclusion can be drawn from the results of the experiments?

Answer: Changes occurred in 2 experiments.

2. Goal setting. Updating the knowledge of students from the course of biology, physics and life safety. Creating a problem situation

Teacher(task): Changes are constantly taking place in the world around us, or in another way we call them phenomena. Give examples of natural phenomena that surround us.

Answer:

  • northern lights;
  • snowfall;
  • hail;
  • storm;
  • rainbow;
  • fog;
  • ball lightning;
  • volcano;
  • earthquake;
  • Hurricane;
  • flood;
  • high water.

Teacher: Pay attention to the "Seasons" attached to the board (autumn, spring).

Question: What happens to substances and bodies?

Answer:

  • leaf rot: a change in the composition of the substance;
  • changing the color of tree leaves in autumn: changing the composition of the substance;
  • melting of ice: the substance does not change, only the state of aggregation (from solid to liquid);
  • the appearance of green color in plants under the influence of sunlight (photosynthesis)

Teacher: What phenomena do you know from physics (the topic was completed: “Change in the states of aggregation of substances”)?

Answer:

  • melting: (t-g) snow melting;
  • crystallization: (f-t) freezing of water;
  • vaporization: (g-d) evaporation of water from the surface of the ocean;
  • condensation: (Ms.) dewfall;
  • sublimation: (t-g) evaporation of naphthalene, melting of graphite, frost;
  • desublimation: (g-t) patterns on glass.

Question: What happens to the substances in the listed phenomena?

Answer: Shape, size, state of aggregation change.

Question: What are such phenomena called?

Answer: Physical.

Teacher: State the topic of our lesson.

Answer: "Physical phenomena and ...." ( worksheet entry, Annex 1).

Question: What other phenomena are there besides physical ones?

Answer: Chemical ( add).

Question: What do we know about them?

Answer: Chemical phenomena are phenomena in which other substances are formed from some substances, therefore they are also called chemical reactions.

Question: What would you like to know about them?

Answer: Learn to identify phenomena, the conditions for their occurrence and course (the purpose of the lesson).

3. Experiment as a way of knowing (group lab/work)

Appendix 2

TB briefing (students) and group work rules (teacher) to voice(Appendix 3, 4).

Experience 1. Paraffin heating. Put a few grains of paraffin on a glass slide with a wooden stick and, grabbing the glass with crucible tongs, carefully heat it over the flame of an alcohol lamp.

Experience 2. Chalk grinding. Pound the chalk in a mortar with a pestle.

Experience 3. Interaction of chalk with HCI (hydrochloric acid). Pour a little solution of the given acid into a test tube and add a little crushed chalk with a wooden stick. Then, light a torch and put it into a test tube.

Experience 4. Interaction of solutions NaHCO 3 (drinking soda), CaCl 2 (calcium chloride). Pour a solution of baking soda into a test tube and add a little calcium chloride to it. Then, light a torch and put it into a test tube.

Experimental results

Name of experience

Observations (what has changed?)

New Substances

Conclusion (What is it?)

1. Heating the paraffin.

State of aggregation

Not formed

Physical

2. Chalk grinding.

Not formed

Physical

3. Interaction of chalk with acid.

Bubble formation

Are formed

Chemical

4. Interaction of solutions of soda and calcium chloride.

The appearance of sediment

Are formed

Chemical

Self-assessment/assessment of the team captain for the contribution made in the discussion of the conclusions by the group (checking the results with the board).

3 experience: candle burning .

Teacher:

Melo, melo all over the earth
To all limits.
The candle burned on the table
The candle was burning.
Like a swarm of midges in summer
Flying into the flame
Flakes flew from the yard
to the window frame.
Snowstorm sculpted on glass
Circles and arrows.
The candle burned on the table
The candle was burning.
(B. Pasternak "Winter Night")

  • What do you see when a candle burns? (changing the shape of paraffin)
  • What happens to the substance? (burning) Why? (heating: light and heat)
  • Why does glass blacken? (digging is formed - coal.) Where did the water on the walls of the glass come from? (product of burning a candle)

Thus, combustion is one of the first reactions mastered by man. For primitive man, fire became a source of heat, a way of protection from wild animals, a means of labor. With its help, people learned to cook food, extract salt, and smelt ore. Combustion was the first process that man learned to control.

4 experience: NaOH with F.F.:

  • What are you watching? (raspberry color solution)
  • What does he testify to? (a chemical reaction has taken place).

4. Analysis and generalization of the obtained results. Conclusion (definition of a chemical reaction). Expansion of information about the new concept (signs of chemical reactions, conditions for their occurrence)

Question: So, how can you know that a chemical reaction has taken place? (exit to signs of chemical reactions). (Entry in the worksheet).

Answer:

  • sludge formation (milk souring);
  • gas release;
  • release of heat and light;
  • color change;
  • the appearance of an odor (sour milk).

Question: What conditions must be met for a reaction to occur?

Answer: (worksheet entry)

  • mixing of substances;
  • heating substances;
  • action of light.

Question: Why do we need to know the conditions for the occurrence and course of chemical reactions?

Answer: In order to control the course of chemical reactions, sometimes a chemical reaction must be stopped, for example, in a fire, we strive to stop the combustion reaction.

Question (task): What fire extinguishers should be used in the following cases:

  • man's clothes on fire
  • ignited gasoline
  • there was a forest fire;
  • oil caught fire on the surface of the water.

Question: Thus, what are the main differences between physical and chemical phenomena? Give examples of them.

Answer:

5. Fixing. Reflection

Exercise 1. From the following phenomena, indicate the chemical phenomena (work in pairs, exchange works for verification):

A). Dissolving sugar in water

B). The decomposition of water by electric current into hydrogen and oxygen

IN). The formation of black plaque on silver products

G). The formation of salt crystals during evaporation of the solution

Task 2. From the list, select signs of a chemical reaction:

A). The appearance of an odor

B). Heating

IN). Emission of gaseous substances

G). Substance contact

D). Color change

AND). Precipitation or dissolution of the precipitate

Z). Good mood

AND). Emission or absorption of heat and/or light

TO). Irradiation with light

L). Communication with each other.

Appendix 5

6. Grades. Homework

7. Summing up the lesson

R. Roland (students read out the words): "The lofty goal of a man of science is to penetrate into the very essence of the observed phenomena, to understand their hidden forces, their laws and currents in order to control them."

The choice of students of the emotional circle: yellow (excellent), green (good), red