Physical phenomena in chemistry examples and meaning. Chemical Phenomena: Examples in Nature and Everyday Life

28.03.2020

Abstract keywords: Physical phenomena, chemical phenomena, chemical reactions, signs chemical reactions, the significance of physical and chemical phenomena.

physical phenomena- These are phenomena in which only the state of aggregation of substances usually changes. Examples of physical phenomena are the melting of glass, the evaporation or freezing of water.

chemical phenomena are the processes by which other substances are formed from these substances. In chemical phenomena, the initial substances are converted into other substances with different properties. Examples of chemical phenomena - combustion of fuel, decay organic matter, rusting of iron, souring of milk.

Chemical phenomena are also called chemical reactions.

Conditions for the occurrence of chemical reactions

The fact that in chemical reactions one substance is converted into another can be judged by outward signs: release of heat (sometimes light), discoloration, odor, precipitation, gas evolution.

For many chemical reactions to start, it is necessary to bring close contact reactants . To do this, they are crushed and mixed; the contact area of the reactants increases. The finest fragmentation of substances occurs when they are dissolved, so many reactions are carried out in solutions.

Grinding and mixing of substances is only one of the conditions for the occurrence of a chemical reaction. For example. when sawdust comes into contact with air at normal temperature, the sawdust does not ignite. In order to start a chemical reaction, in many cases it is necessary to heat the substances to a certain temperature.

It is necessary to distinguish between concepts "conditions of occurrence" And "conditions for the flow of chemical reactions" . So, for example, in order to start combustion, heating is needed only at the beginning, and then the reaction proceeds with the release of heat and light, and further heating is not required. And in the case of water decomposition, the influx of electrical energy is necessary not only to start the reaction, but also for its further flow.

The most important conditions for the occurrence of chemical reactions are:

thorough grinding and mixing of substances;
preheating substances to a certain temperature.

Significance of physical and chemical phenomena

Chemical reactions are of great importance. They are used to obtain metals, plastics, mineral fertilizers, medicines, etc., and also serve as a source of various types of energy. So, during the combustion of fuel, heat is released, which is used in everyday life and in industry.

All vital processes (respiration, digestion, photosynthesis, etc.) occurring in living organisms are also associated with various chemical transformations. For example, chemical transformations of substances contained in food (proteins, fats, carbohydrates) occur with the release of energy, which is used by the body to ensure vital processes.

For the last 200 years of humanity 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 are exposed to many things. 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 exhaustion natural resources of our planet, chemists now face an important task: to develop and implement methods by which it is possible to obtain artificially, in a laboratory or industrial production, 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 fuels are being developed that would be just as efficient, but would not pollute 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). Known substances that cannot exist in normal conditions in all three aggregate states. 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 physical properties ah many substances are collected in specialized 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 - solid bodies, having the form 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 a few 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

The chemical reaction is depicted in general view reaction scheme REAGENTS -> PRODUCTS

Where 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. TOTAL

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)

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The world around us, with all its richness and diversity, lives according to laws that are quite easy to explain with the help of such sciences as physics and chemistry. And even at the basis of the life of such complex organism, like man, lies nothing but chemical phenomena and processes.

Definitions and examples

An elementary example is a kettle put on fire. After a while, the water will begin to heat up, then boil. We will hear a characteristic hiss, jets of steam will fly out of the neck of the kettle. Where did it come from, because it was not originally in the dishes! Yes, but water, at a certain temperature, begins to turn into a gas, changes its physical state from liquid to gaseous. Those. it remained the same water, only now in the form of steam. This

And we will see chemical phenomena if we put a bag of tea leaves in boiling water. Water in a glass or other vessel will turn red-brown. A chemical reaction will take place: under the influence of heat, the tea leaves will begin to steam, releasing color pigments and taste properties inherent in this plant. We will get a new substance - a drink with specific properties peculiar only to it. quality characteristics. If we add a few tablespoons of sugar there, it will dissolve (physical reaction), and the tea will become sweet. Thus, physical and chemical phenomena are often related and interdependent. For example, if the same tea bag is placed in cold water, no reaction will occur, tea leaves and water will not interact, and sugar will not want to dissolve either.

Thus, chemical phenomena are those in which some substances turn into others (water into tea, water into syrup, firewood into ash, etc.). Otherwise, a chemical phenomenon is called a chemical reaction.

Physical phenomena are called phenomena in which the chemical composition of a substance remains the same, but the size of the body, shape, etc. changes. (a deformed spring, water frozen into ice, a tree branch broken in half).

Conditions for occurrence and occurrence

We can judge whether chemical and physical phenomena occur by certain signs and changes that are observed in a particular body or substance. So, most chemical reactions are accompanied by the following "identification marks":

as a result or during the course of such a precipitate precipitates;
there is a change in the color of the substance;
gas can be released, for example, carbon monoxide during combustion;
there is an absorption or, conversely, the release of heat;
light emission is possible.

In order for chemical phenomena to be observed, i.e. reactions occur, certain conditions are necessary:

the reacting substances must be in contact, be in contact with each other (i.e., the same tea leaves must be poured into a mug of boiling water);
it is better to grind the substances, then the reaction will proceed faster, the interaction will occur sooner (sugar-sand is more likely to dissolve, melt in hot water than lumpy);
in order for many reactions to occur, it is necessary to change the temperature regime of the reacting components, cooling or heating them to a certain temperature.

You can observe the chemical phenomenon empirically. But you can describe it on paper using a chemical chemical reaction).

Some of these conditions also work for the occurrence of physical phenomena, for example, a change in temperature or direct contact of objects, bodies with each other. For example, if you hit the head of a nail hard enough with a hammer, it can deform, lose its usual shape. But she will remain a nail head. Or, when you turn on the electric lamp in the network, the tungsten filament inside it will begin to warm up and glow. However, the substance from which the thread is made will remain the same tungsten.

The description of physical processes and phenomena occurs through physical formulas, solution of physical problems.

Dynamic change is built into nature itself. Everything changes in one way or another every moment. If you look closely, you will find hundreds of examples of physical and chemical phenomena that are quite natural transformations.

Change is the only constant in the universe

Ironically, change is the only constant in our universe. In order to understand physical and chemical phenomena (examples in nature are found at every turn), it is customary to classify them into types, depending on the nature of the end result caused by them. There are physical, chemical and mixed changes, which contain both the first and the second.

Physical and chemical phenomena: examples and meaning

What is a physical phenomenon? Any change that occurs in a substance without changing it chemical composition, are physical. They are characterized by changes in physical attributes and material state (solid, liquid or gaseous), density, temperature, volume, which occur without changing its fundamental chemical structure. There is no creation of new chemical products or changes in the total mass. In addition, this type of change is usually temporary and in some cases completely reversible.

When you mix chemicals in the lab, you can easily see the reaction, but there are many chemical reactions going on in the world around you every day. A chemical reaction changes molecules, while a physical change only rearranges them. For example, if we take chlorine gas and metallic sodium and combine them, we get table salt. The resulting substance is very different from any of its constituents. This is a chemical reaction. If we then dissolve this salt in water, we simply mix the salt molecules with the water molecules. There is no change in these particles, it is a physical transformation.

Examples of physical changes

Everything is made up of atoms. When atoms combine, different molecules are formed. The different properties that objects inherit are the result of different molecular or atomic structures. The main properties of an object depend on their molecular arrangement. Physical changes occur without changing the molecular or atomic structure of objects. They simply transform the state of an object without changing its nature. Melting, condensation, volume change and evaporation are examples of physical phenomena.

Additional examples of physical changes: metal expanding when heated, sound transmission through air, water freezing into ice in winter, copper being drawn into wires, clay forming on various objects, ice cream melting to a liquid, heating metal and changing it into another form, sublimation of iodine when heating, the fall of any object under the influence of gravity, the ink is absorbed by chalk, the magnetization of iron nails, a snowman melting in the sun, glowing incandescent lamps, magnetic levitation of an object.

How to distinguish between physical and chemical changes?

Many examples of chemical and physical phenomena can be found in life. It is often difficult to tell the difference between the two, especially when both can occur at the same time. To identify physical changes, ask the following questions:

Is the state of an object's state a change (gaseous, solid, and liquid)?
Is the change a purely limited physical parameter or characteristic such as density, shape, temperature, or volume?
Is the chemical nature of an object a change?
Are there chemical reactions that lead to the creation of new products?

If the answer to one of the first two questions is yes, and there are no answers to the subsequent questions, it is most likely a physical phenomenon. Conversely, if the answer to any of the last two questions is yes, while the first two are no, then it is definitely a chemical phenomenon. The trick is just to clearly observe and analyze what you see.

Examples of chemical reactions in everyday life

Chemistry takes place in the world around you, not just in the laboratory. Matter interacts to form new products through a process called chemical reaction or chemical change. Every time you cook or clean, it's chemistry in action. Your body lives and grows through chemical reactions. There are reactions when you take medicine, light a match and sigh. Here are 10 chemical reactions in everyday life. This is just a small selection of those examples of physical and chemical phenomena in life that you see and experience many times every day:

Photosynthesis. Chlorophyll in plant leaves converts carbon dioxide and water into glucose and oxygen. It is one of the most common daily chemical reactions and also one of the most important because it is how plants produce food for themselves and animals and convert carbon dioxide into oxygen.
Aerobic cellular respiration is a reaction with oxygen in human cells. Aerobic cellular respiration is the opposite process of photosynthesis. The difference is that energy molecules combine with the oxygen we breathe to release the energy our cells need, as well as carbon dioxide and water. The energy used by cells is chemical energy in the form of ATP.
Anaerobic respiration. Anaerobic respiration produces wine and other fermented foods. Your muscle cells perform anaerobic respiration when you run out of oxygen, such as during intense or prolonged exercise. Anaerobic respiration by yeast and bacteria is used for fermentation to produce ethanol, carbon dioxide and other chemical substances that produce cheese, wine, beer, yogurt, bread and many other common foods.
Combustion is a type of chemical reaction. This is a chemical reaction in everyday life. Every time you light a match or a candle, light a fire, you see a combustion reaction. Incineration combines energy molecules with oxygen to produce carbon dioxide and water.
Rust is a common chemical reaction. Over time, the iron develops a red, flaky coating called rust. This is an example of an oxidation reaction. Other everyday examples include the formation of verdigris on copper and the tarnishing of silver.
Mixing chemicals causes chemical reactions. Baking powder and baking soda perform similar functions in baking, but they react differently to other ingredients, so you can't always swap them out. If you combine vinegar and baking soda for a chemical "volcano" or milk with baking powder in a recipe, you are experiencing a double bias or metathesis reaction (plus a few others). The ingredients are recombined to produce carbon dioxide gas and water. The carbon dioxide forms bubbles and helps the baked goods "grow". These reactions appear simple in practice, but often involve multiple steps.
Batteries are examples of electrochemistry. Batteries use electrochemical or redox reactions to convert chemical energy into electrical energy.
Digestion. Thousands of chemical reactions take place during digestion. As soon as you put food in your mouth, an enzyme in your saliva called amylase begins to break down sugars and other carbohydrates into simpler forms that your body can absorb. The hydrochloric acid in your stomach reacts with food to break it down, and enzymes break down proteins and fats so they can be absorbed into the bloodstream through the intestinal wall.
Acid-base reactions. Whenever you mix an acid (such as vinegar, lemon juice, sulfuric acid, hydrochloric acid) with an alkali (e.g. baking soda, soap, ammonia, acetone), you are performing an acid-base reaction. These processes neutralize each other, producing salt and water. Sodium chloride is not the only salt that can be formed. For example, here is the chemical equation for an acid-base reaction that produces potassium chloride, a common substitute for table salt: HCl + KOH → KCl + H 2 O.
Soap and detergents. They are purified by chemical reactions. Soap emulsifies dirt, which means that oily stains bind to the soap so that they can be removed with water. Detergents reduce the surface tension of water, so they can interact with oils, sequester them, and wash them away.
Chemical reactions in food preparation. Cooking is one big hands-on chemistry experiment. Cooking uses heat to evoke chemical changes in food. For example, when you boil an egg hard, the hydrogen sulfide produced by heating the egg white can react with the iron from the egg yolk, forming a grey-green ring around the yolk. When you cook meat or baked goods, the Maillard reaction between amino acids and sugars produces a brown color and desirable flavor.

Other examples of chemical and physical phenomena

Physical properties describe characteristics that do not change a substance. For example, you can change the color of paper, but it's still paper. You can boil water, but when you collect and condense the steam, it's still water. You can determine the mass of a sheet of paper and it's still paper.

Chemical properties are those that indicate how a substance reacts or does not react with other substances. When sodium metal is placed in water, it reacts violently to form sodium hydroxide and hydrogen. Sufficient heat is generated by the hydrogen escaping into the flame by reacting with the oxygen in the air. On the other hand, when you put a piece of copper metal into water, there is no reaction. So the chemical property of sodium is that it reacts with water, but the chemical property of copper is that it does not.

What other examples of chemical and physical phenomena can be given? Chemical reactions always occur between electrons in the valence shells of the atoms of elements in periodic table. Physical phenomena at low energy levels simply include mechanical interactions - random collisions of atoms without chemical reactions, such as atoms or gas molecules. When the collision energies are very high, the integrity of the nucleus of atoms is broken, leading to division or fusion of the species involved. Spontaneous radioactive decay is usually considered a physical phenomenon.

Goals: know

1) features of physical and chemical phenomena;

2) signs of chemical reactions.

1) distinguish between physical and chemical phenomena;

2) recognize chemical reactions by signs.

During the classes

I. Organizational moment

Hello kids, sit down. Let's start the chemistry lesson.

II. Message about the topic and purpose of the lesson

The topic of our lesson is “Physical and chemical phenomena. Signs of chemical reactions ”(write in a notebook).

Today we will have to learn about physical and chemical phenomena and the signs of chemical reactions. This is what we must find out.

What should we be able to do with you? And we will have to be able to distinguish chemical phenomena from physical ones and recognize chemical reactions by signs.

III. Learning new material

So let's start.

Teacher: Everything in the world is in motion, everything changes. Changes that occur with substances are called phenomena. For example: evaporation of water, melting of iron, rusting of metals, etc. There are physical and chemical phenomena.

Physical phenomena are accompanied by a change in shape, state of aggregation, volume, temperature, degree of grinding of a substance, etc., but there is no transformation of one substance into another. The composition of the substance remains unchanged.

For example, the melting of ice or the boiling of water are physical phenomena and here the state of aggregation of matter changes, while the substance itself - water remains unchanged. In this case, there is a change in the physical properties of the substance.

In addition to physical properties, each substance has certain chemical properties.

Chemical properties Substance is the ability of a given substance to transform into other substances. The chemical properties of substances are manifested in chemical phenomena.

Chemical phenomena, which are called chemical reactions, are accompanied by the transformation of one substance into another.

As a result of a chemical reaction, new substances are always formed that differ from the original composition and properties.

Thus, during physical phenomena, the qualitative and quantitative and quantitative composition of substances is preserved, while the chemical composition of the initial substances is not preserved, they turn into other substances.

At home you were offered creative task- compose a story about a meeting with physical and chemical phenomena or draw what you see. So guys, who's ready?

In the meantime, stories will be heard, everyone else will have to think about what kind of phenomenon they are talking about, physical or chemical.

Guys, please.

Student 1: From biology, you know that potato tubers contain starch, which is formed in the leaves in the light and then deposited in the tubers. If you take this tuber to cut and drop tincture of iodine on the cut, then the brown color of iodine will turn into blue. This happened because a reaction took place between starch and iodine, and a new substance was formed. of blue color, (demonstrates experience).

Okay, well done, sit down.

Guys, what do you think, what phenomenon did the student talk about?

Students: It was about a chemical phenomenon.

What do you think?

That's right, it's a chemical phenomenon.

Who else is ready?

Well done, okay, sit down.

Guys, what is this phenomenon?

Students: Again, it was a matter of chemistry.

Who else thinks?

Well done, good guys, correctly answered. Let's listen to the student.

3 student: And I, studying literature for young chemists, decided to do such an experiment at home. I took a glass of soapy water, added a few drops of table vinegar and found that instead of foam, the liquid contained light gray flakes of sediment, let's see what happens (demonstrates experience).

Well done, okay, sit down. What phenomenon did the Student tell us about?

Pupils: Here it was told about a chemical phenomenon. (Who else can say?)

That's right, kids, it's a chemical phenomenon.

Who else prepared the show?

Please listen.

4 student: And I decided to draw my phenomena. See what I did and listen to my story.

Clear hot day (shows a picture). Water evaporates from the surface of the earth in the form of steam, which is always in the air. The farther from the surface of the earth, the lower the temperature, and therefore tiny droplets of water are formed from the steam. Fog is made up of these droplets. Clouds are the same fog in the air high above the ground (changes the picture). Small droplets, merging in the clouds, with each other, gradually increase. The cloud darkens and becomes a cloud. Heavy drops of water cannot stay in the air and fall to the ground in the form of rain (changes pattern). In winter, snowflakes form from steam. Reservoirs freeze in winter, covered with ice. That's where the fun kids are. So, guys, what phenomena did I present to you?

Students: Here are physical phenomena, namely the change in the state of aggregation of water.

Well done, sit down, well prepared work.

Student 5: I depicted the process of washing hands. When we wash our hands with soap, the soap in the water breaks down into two substances: an alkali and a fatty acid. The alkali binds the fat that covers our skin, and the fatty acid forms a rich foam. The foam captures and, together with the water, takes away all the smallest particles of dirt that were on our skin.

6 student: This figure shows the process of preparing the test. After kneading the flour, add sugar, butter, yeast. Some of the starch in flour is converted into sugar. Yeast immediately “pounces” on this sugar and decomposes sugar into alcohol and carbon dioxide. In the dough, the gas tends to escape and in doing so it rises and loosens the dough. This is why the dough becomes porous and the bread or cake is riddled with holes.

And here there are a number of chemical reactions.

Okay, well done, sit down. You are right to understand the material. All participants creative work I put a mark “5” (six ratings).

So, guys, what are the phenomena called physical?

Students: Physical phenomena are phenomena that are accompanied by changes in shape, state of aggregation, volume, temperature, degree of grinding, while there is no transformation of some substances into others. The composition of the substance remains unchanged.

Okay, well done, sit down. What are chemical phenomena? Who will say?

Students: Chemical phenomena are phenomena that are accompanied by the transformation of one substance into another. In this case, the composition of the initial substances is not preserved, and in the course of a chemical reaction they turn into other substances.

Well done, okay, right, sit down.

So, let's once again comment on the performance of your classmates. (On the desk) -

Reactive Substance Sign of a Chemical Reaction

By clicking, reacting substances appear immediately, then signs of these reactions:

Let's open notebooks and write down the signs of a chemical reaction. We wrote down the title “Signs of chemical reactions”.

Color change.
Gas release.
Precipitation.

And the topic of our lesson is “Signs of chemical reactions”.

So how are chemical reactions recognized? (We list).

But this is not all the signs, there are a number of other signs that I will tell you about now.

Attention, children, we continue to study a new topic. Now I will show you experiments that are accompanied by signs that we have already talked about and those that you still do not know about.

(I demonstrate experiments with signs of chemical reactions from the disk “School chemical experiment” grade 8, part 1):

precipitation;
sediment dissolution;
color change;
sound effect;
gas release.

So, by what signs are chemical reactions recognized.

Student: Lists signs of chemical reactions and writes down in a notebook.

Who will repeat? Another student repeats.

Okay, well done, and now children, let's have a rest! And then I see - you are tired.

(Fizminutka)

So, let's move on to fixing.

IV. Fixing the material

Guys, open the textbooks paragraph 28 page 97. Look carefully, find:

An example of a color change reaction and read out. Who found? Please ... And what example did we consider?

A chemical reaction that proceeds with the formation of a precipitate ... And what was an example in our lesson?

With gas release? And in the lesson, what experience did we have with such a sign?

With heat release.

With color change.

With an odor.

So what are the characteristics of chemical reactions?

Attention, let's move on to the next work. As a reinforcement, you will complete test tasks (Appendix 1) and make a self-assessment. There are tests on the tables. Answer options are given for each question. You will need to choose the correct answer (one or more) and circle it. But first, do not forget to write your first and last name on the piece of paper. We carry out (5-7 minutes).

Now let's check how you understood the topic of the lesson. Exchange sheets with each other and check the test for the key (I bring the key with the correct answers to the board). Look at the board and check your answer. If the answer is incorrect, cross out and circle the correct one. If there are no errors - put "5". If 1-2 mistakes are made “4”. If more than 2 errors - “3”.

Have you checked? Honestly tell who got "5", who got "4", who got "3".

Well done, you have mastered the topic well!

So guys, what did you learn in the lesson?

Student: We learned what are the signs of chemical reactions.

What work have we done?

Student: We completed creative tasks, demonstrated experiments and drawings, and also watched video clips “Signs of chemical reactions”

And what have we learned?

Student: We learned to recognize chemical reactions by signs.

What else?

Student: Fixed the methodology for performing tests.

Well done guys, good job.

So, what signs of chemical reactions do you know? (student answers)

Well done guys, well learned the new topic.

VI. Homework

And now the homework: to study paragraph 28, No. 1,2 - mandatory for everyone, and No. 3 - for students with "4" and "5" in the subject.

Recorded homework, the lesson is over. Goodbye.

Literature:

textbook “Chemistry. 8th grade". I.I. Novoshinsky, N.S. Novoshinskaya;
A. Khrapovsky. Entertaining essays on chemistry; I. Volper. Young chemists.