Chemical phenomena in our life. Chemical phenomena in everyday life and everyday life

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Zaporozhye secondary school of І-ІІІ levels № 90

Chemical phenomena in everyday life and everyday life

7th grade student

Dmitry Baluev

Introduction

chemical reaction fuel oxidation

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 the life of such a complex organism as a person is based on nothing more than chemical phenomena and processes.

Surely, you have noticed more than once something like how mom's silver ring darkens over time. Or how a nail rusts. Or how wooden logs burn to ash. But even if your mother does not like silver, and you have never gone hiking, you have seen exactly how a tea bag is brewed in a cup.

What do all these examples have in common? And the fact that they are all chemical phenomena.

So, the most common examples of chemical phenomena in life and everyday life:

nail rusting

fuel combustion

precipitation

grape juice fermentation

paper rot

perfume synthesis

darkening silver earring

the appearance of green plaque on bronze

scale formation in boilers

extinguishing soda with vinegar

rotten meat

burning paper

Want details? 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 is a physical phenomenon.

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, unique quality characteristics. If we add a few tablespoons of sugar there, it will dissolve (physical reaction), and the tea will become sweet (chemical reaction). 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.

We can judge whether chemical 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 equation (the equation of a 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.

But let's look at a few more examples. After all, we all understand that chemistry occurs not only in test tubes in the school laboratory.

1. Chemical phenomena in everyday life

These include those that can be observed in the daily life of modern man. Some of them are quite simple and obvious, anyone can observe them in their kitchen, as an example with brewing tea.

Using the example of strong (concentrated) tea brewing, you can independently conduct another experiment: lighten tea with a slice of lemon. Due to the acids contained in lemon juice, the liquid will once again change its composition.

What other phenomena can you observe in everyday life? For example, chemical phenomena include the process of fuel combustion in an engine.

To simplify, the reaction of fuel combustion in the engine can be described as follows: oxygen + fuel = water + carbon dioxide.

In general, several reactions take place in the chamber of an internal combustion engine, in which fuel (hydrocarbons), air and an ignition spark are involved. Or rather, not just fuel - a fuel-air mixture of hydrocarbons, oxygen, nitrogen. Before ignition, the mixture is compressed and heated.

The combustion of the mixture occurs in a fraction of a second, as a result, the bond between the hydrogen and carbon atoms is destroyed. Due to this, a large amount of energy is released, which sets the piston in motion, and that - the crankshaft.

Subsequently, hydrogen and carbon atoms combine with oxygen atoms, water and carbon dioxide are formed.

Ideally, the complete combustion reaction should look like this: CnH2n+2 + (1.5n+0.5)O2 = nCO2 + (n+1)H2O. In reality, internal combustion engines are not that efficient. Suppose that if oxygen is not enough during the reaction, CO is formed as a result of the reaction. And with a greater lack of oxygen, soot is formed (C).

The formation of plaque on metals as a result of oxidation (rust on iron, patina on copper, darkening of silver) is also from the category of household chemical phenomena.

Let's take iron as an example. Rusting (oxidation) occurs under the influence of moisture (air humidity, direct contact with water). The result of this process is iron hydroxide Fe2O3 (more precisely, Fe2O3 * H2O). You may see it as a loose, rough, orange or reddish-brown coating on the surface of metal products.

Another example is the green coating (patina) on the surface of copper and bronze items. It is formed over time under the influence of atmospheric oxygen and humidity: 2Cu + O2 + H2O + CO2 = Cu2CO5H2 (or CuCO3 * Cu(OH)2). The resulting basic copper carbonate is also found in nature in the form of the mineral malachite.

And another example of a slow oxidative reaction of a metal in domestic conditions is the formation of a dark coating of silver sulfide Ag2S on the surface of silver items: jewelry, cutlery, etc.

The “responsibility” for its occurrence is borne by sulfur particles, which are present in the form of hydrogen sulfide in the air that we breathe. Silver can also darken upon contact with sulfur-containing foods (eggs, for example). The reaction looks like this: 4Ag + 2H2S + O2 = 2Ag2S + 2H2O.

Let's go back to the kitchen. Here you can consider a few more curious chemical phenomena: the formation of scale in the kettle is one of them.

In domestic conditions, there is no chemically pure water; metal salts and other substances are always dissolved in it in various concentrations. If the water is saturated with calcium and magnesium salts (hydrocarbonates), it is called hard. The higher the salt concentration, the harder the water.

When such water is heated, these salts decompose into carbon dioxide and an insoluble precipitate (CaCO3 and MgCO3). You can observe these solid deposits by looking into the kettle (and also by looking at the heating elements of washing machines, dishwashers, and irons).

In addition to calcium and magnesium (from which carbonate scale is formed), iron is also often present in water. During the chemical reactions of hydrolysis and oxidation, hydroxides are formed from it.

By the way, when you are about to get rid of scale in the kettle, you can observe another example of entertaining chemistry in everyday life: ordinary table vinegar and citric acid do well with deposits. A kettle with a solution of vinegar / citric acid and water is boiled, after which the scale disappears.

And without another chemical phenomenon, there would be no delicious mother's pies and buns: we are talking about extinguishing soda with vinegar.

When mom extinguishes soda in a spoon with vinegar, the following reaction occurs: NaHCO3 + CH3COOH = CH3COONa + H2O + CO2. The resulting carbon dioxide tends to leave the dough - and thereby changes its structure, makes it porous and loose.

By the way, you can tell your mother that it is not at all necessary to extinguish the soda - she will react anyway when the dough gets into the oven. The reaction, however, will go a little worse than when quenching soda. But at a temperature of 60 degrees (and preferably 200), soda decomposes into sodium carbonate, water and the same carbon dioxide. True, the taste of ready-made pies and buns may be worse.

The list of household chemical phenomena is no less impressive than the list of such phenomena in nature. Thanks to them, we have roads (asphalt making is a chemical phenomenon), houses (brick firing), beautiful fabrics for clothes (dyeing). If you think about it, it becomes clearly clear how multifaceted and interesting the science of chemistry is. And how much benefit can be derived from understanding its laws.

2. Interesting chemical phenomena

I would like to add some interesting things. Among the many, many phenomena invented by nature and man, there are special ones that are difficult to describe and explain. They include the burning of water. How can this be, you ask, because water does not burn, it extinguishes fire? How can she burn? And here's the thing.

The combustion of water is a chemical phenomenon in which oxygen-hydrogen bonds are broken in water with an admixture of salts under the influence of radio waves. The result is oxygen and hydrogen. And, of course, it is not the water itself that burns, but hydrogen.

At the same time, it reaches a very high combustion temperature (more than one and a half thousand degrees), plus water is again formed during the reaction.

This phenomenon has long been of interest to scientists who dream of learning how to use water as a fuel. For example, for cars. So far, this is something from the realm of fantasy, but who knows what scientists will be able to invent very soon. One of the main snags is that when water burns, more energy is released than is spent on the reaction.

By the way, something similar can be observed in nature. According to one theory, large single waves, appearing as if from nowhere, are actually the result of a hydrogen explosion. The electrolysis of water, which leads to it, is carried out due to the ingress of electrical discharges (lightning) on ​​the surface of the salt water of the seas and oceans.

But not only in water, but also on land, one can observe amazing chemical phenomena. If you had a chance to visit a natural cave, you would surely be able to see there bizarre, beautiful natural "icicles" hanging from the ceiling - stalactites. How and why they appear is explained by another interesting chemical phenomenon.

A chemist, looking at a stalactite, sees, of course, not an icicle, but calcium carbonate CaCO3. The basis for its formation is sewage, natural limestone, and the stalactite itself is built due to the precipitation of calcium carbonate (growth down) and the adhesion force of atoms in the crystal lattice (growth in breadth).

By the way, similar formations can rise from the floor to the ceiling - they are called stalagmites. And if stalactites and stalagmites meet and coalesce into solid columns, they are called stalagnates.

Conclusion

Many amazing, beautiful, as well as dangerous and frightening chemical phenomena occur in the world every day. From many, people have learned to benefit: they create building materials, cook food, make vehicles travel long distances, and much more.

Without many chemical phenomena, the existence of life on earth would not be possible: without the ozone layer, people, animals, plants would not survive due to ultraviolet rays. Without plant photosynthesis, animals and people would have nothing to breathe, and without the chemical reactions of respiration, this issue would not be relevant at all.

Fermentation makes it possible to cook food, and the similar chemical phenomenon of putrefaction decomposes proteins into simpler compounds and returns them to the cycle of substances in nature.

The formation of oxide when copper is heated, accompanied by a bright glow, the burning of magnesium, the melting of sugar, etc., are also considered chemical phenomena. And find them a useful use.

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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 the life of such a complex organism as a person is based on nothing more than 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. it

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, unique 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, the solution of physical problems.

2014-06-04

Familiarization with mixtures and physical phenomena allowed you to conclude that even in mixtures, when physical phenomena are performed, the composition of substances remains unchanged, and the components of mixtures retain their properties. So, during the melting of ice, boiling and freezing of water, its molecules are preserved.

chemical phenomena. Chemical phenomena are fundamentally different from physical ones. By the beginning of a chemical phenomenon, some substances exist, after it they turn into others.

Chemical phenomena are changes in which one substance is transformed into another. they are also called chemical reactions.

To make sure that a chemical phenomenon has occurred, it is necessary to detect the formation of new substances. The easiest way to do this is when our vision captures the signs of a chemical phenomenon: gas evolution, precipitation, color change, the appearance of light and heat. In those shown in Fig. 39 (see p. 64) examples of chemical phenomena present these features.

Signs of chemical phenomena include the appearance of smell. It is enough to keep meat products in the refrigerator for several days and even hours in the summer, as

Provide evidence that in mixtures their components retain their properties.

The fact that a chemical phenomenon has occurred is evidenced by the appearance of an unpleasant odor.

Signs of chemical phenomena are the release of gas, the formation of a precipitate, a change in color, the appearance of smell, light and heat.

Decay is a natural chemical phenomenon. Have you ever thought about why we don’t “drown” in a disgraced letter in a dense forest and where fallen branches of trees, fruits, dried grass disappear in nature? Indeed, there is something to think about and learn from nature, so as not to have trouble with garbage.

It turns out that under favorable conditions, the dead remains of plants and animals rot. Decay is a natural chemical phenomenon during which organic substances, mainly proteins, are converted into other organic as well as inorganic substances. As a result, the soil is enriched with nutrients (humus, or humus). Rotting is promoted by humidity, bacteria, limited air access. A sign of this natural chemical phenomenon is the release of heat.

As a result of decay, simple substances are formed, they enter the soil, water, air and are again absorbed by plants and participate in the formation of new organic substances.

Due to decay, dead remains of organisms do not accumulate, and the soil is enriched with humus.

This is important in nature. A chemical phenomenon in the life of a line is not always desirable, since through it food products become unfit for consumption. Ways to prevent the decay of organic food substances are canning, boiling, salting, freezing.

Many chemical phenomena take place in nature.

So in plants from carbon dioxide and water, organic substances and oxygen necessary for life are formed. Thanks to chemical phenomena, the organism of animals and humans receives all the substances necessary for growth and development.

piggy bank of knowledge

People have learned to carry out chemical phenomena in laboratories and factories. How important this is now, you are constantly convinced. First of all, the production of metals, rubber and rubber, plastics, roof and floor coverings, cement, fertilizers for plants, food additives for animals should be mentioned. Each of these industries was mastered by a person at different times. By studying history, you will learn about the Bronze and Iron Ages. The names confirm the importance of the chemical phenomena mastered by the people, thanks to which she managed to replace the stone spear, wooden harrow with metal tools.

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:

№, Phenomenon name	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

>> Physical and chemical phenomena (chemical reactions). Experimenting at home. External effects in chemical reactions

Physical and chemical phenomena (chemical reactions)

The material of the paragraph will help you find out:

> what is the difference between physical and chemical phenomena.(chemical reactions);
> what external effects accompany chemical reactions.

In the lessons of natural history, you learned that various physical and chemical phenomena occur in nature.

physical phenomena.

Each of you has repeatedly observed how ice melts, water boils or freezes. Ice, water and water vapor consist of the same molecules, therefore they are one substance (in different states of aggregation).

Phenomena in which a substance does not change into another is called physical.

Physical phenomena include not only the change of substances, but also the glow of hot bodies, the passage of electric current in metals, the spread of the smell of substances in the air, the dissolution of fat in gasoline, the attraction of iron to a magnet. Such phenomena are studied by the science of physics.

Chemical phenomena (chemical reactions).

One of the chemical phenomena is combustion. Consider the process of burning alcohol (Fig. 46). It occurs with the participation of oxygen, which is contained in the air. Burning, alcohol, it would seem, passes into a gaseous state, just as water turns into steam when heated. Ho it's not. If the gas obtained as a result of the combustion of alcohol is cooled, then part of it will condense into a liquid, but not into alcohol, but into water. The rest of the gas will remain. With the help of additional experience, it can be proved that this residue is carbon dioxide.

Rice. 46. ​​Burning alcohol

Thus the alcohol that burns, and oxygen, which is involved in the combustion process, are converted into water and carbon dioxide.

Phenomena in which one substance is converted into another, called chemical phenomena, or chemical reactions.

Substances that enter into a chemical reaction are called initial substances, or reagents, and those that are formed are called final substances, or reaction products.

The essence of the considered chemical reaction is conveyed by the following record:

alcohol + oxygen -> water + carbon dioxide
starting materials final substances
(reagents) (reaction products)

The reactants and products of this reaction are made up of molecules. During combustion, a high temperature is created. Under these conditions, the molecules of the reagents break down into atoms, which, when combined, form the molecules of new substances - products. Therefore, all atoms are conserved during the reaction.

If the reactants are two ionic substances, then they exchange their ions. Other variants of the interaction of substances are also known.

External effects accompanying chemical reactions.

By observing chemical reactions, you can fix the following effects:

Color change (Fig. 47, a);
gas release (Fig. 47, b);
the formation or disappearance of sediment (Fig. 47, c);
the appearance, disappearance or change of smell;
release or absorption of heat;
the appearance of a flame (Fig. 46), sometimes a glow.

Rice. 47. Some external effects in chemical reactions: a - the appearance
coloring; b - gas evolution; c - the appearance of sediment

Lab experience #3

The appearance of color as a result of the reaction

Are soda ash and phenolphthalein solutions colored?

Add 2 drops of phenolphthalein solution to a portion of the I-2 soda solution. What color appeared?

Laboratory experiment No. 4

Emission of gas as a result of the reaction

Add a little hydrochloric acid to the soda ash solution. What are you watching?

Laboratory experiment No. 5

The appearance of a precipitate as a result of the reaction

Add 1 ml of copper sulphate solution to the soda ash solution. What's happening?

The appearance of a flame is a sign of a chemical reaction, that is, it indicates precisely a chemical phenomenon. Other external effects can also be observed during physical phenomena. Let's give some examples.

Example 1 Silver powder obtained in a test tube as a result of a chemical reaction has a gray color. If it is melted and then the melt is cooled, we get a piece of metal, but not gray, but white, with a characteristic luster.

Example 2 If natural water is heated, then gas bubbles will begin to be released from it long before boiling. It is dissolved air; its solubility in water decreases when heated.

Example 3. An unpleasant smell in the refrigerator disappears if silica gel granules, one of the Silicium compounds, are placed in it. Silica gel absorbs molecules of various substances without destroying them. Activated charcoal in a gas mask works similarly.

Example 4 . When water turns into steam, heat is absorbed, and when water freezes, heat is released.

To determine whether a transformation has taken place - physical or chemical, one should carefully observe it, as well as comprehensively examine the substances before and after the experiment.

Chemical reactions in nature, everyday life and their significance.

Chemical reactions are constantly taking place in nature. Substances dissolved in rivers, seas, oceans interact with each other, some react with oxygen. Plants absorb carbon dioxide from the atmosphere, from the soil - water, substances dissolved in it and process them into proteins, fats, glucose, starch, vitamins, other compounds, as well as oxygen.

It is interesting

As a result of photosynthesis, about 300 billion tons of carbon dioxide are absorbed from the atmosphere annually, 200 billion tons of oxygen are released, and 150 billion tons of organic substances are formed.

Reactions involving oxygen, which enters living organisms during respiration, are very important.

Many chemical reactions accompany us in everyday life. They occur during the roasting of meat, vegetables, baking bread, sour milk, fermentation of grape juice, bleaching of fabrics, burning of various types of fuel, hardening of cement and alabaster, blackening of silver jewelry over time, etc.

Chemical reactions form the basis of such technological processes as the production of metals from ores, the production of fertilizers, plastics, synthetic fibers, drugs, and other important substances. By burning fuel, people provide themselves with heat and electricity. With the help of chemical reactions, toxic substances are neutralized, industrial and domestic waste is processed.

Certain reactions lead to negative consequences. The rusting of iron reduces the life of various mechanisms, equipment, vehicles, and leads to large losses of this metal. Fires destroy housing, industrial and cultural facilities, historical values. Most foods spoil due to their interaction with oxygen in the air; in this case, substances are formed that have an unpleasant odor, taste and are harmful to humans.

conclusions

Physical phenomena are phenomena in which each substance is preserved.

Chemical phenomena, or chemical reactions, are the transformations of one substance into another. They can be accompanied by various external effects.

Many chemical reactions occur in the environment, in plants, animal and human organisms, accompany us in everyday life.

?
100. Find a match:

1) dynamite explosion; a) a physical phenomenon;
2) solidification of molten paraffin; b) a chemical phenomenon.
3) burning food in a pan;
4) the formation of salt during the evaporation of sea water;
5) separation of a highly agitated mixture of water and vegetable oil;
6) fading of dyed fabric in the sun;
7) the passage of electric current in the metal;

101. What external effects are accompanied by such chemical transformations: a) burning a match; b) rust formation; c) fermentation of grape juice.

102. Why do you think some food products (sugar, starch, vinegar, salt) can be stored indefinitely, while others (cheese, butter, milk) spoil quickly?

Experimenting at home

External effects in chemical reactions

1. Prepare small amounts of aqueous solutions of citric acid and baking soda. Pour together portions of both solutions into a separate beaker. What's happening?

Add some soda crystals to the rest of the citric acid solution, and a few citric acid crystals to the rest of the soda solution. What effects do you observe - the same or different?

2. Pour some water into three small glasses and add 1-2 drops of an alcohol solution of brilliant green, known as greenery, to each. Add a few drops of ammonia to the first glass, and a solution of citric acid to the second. Has the color of the dye (brilliant green) changed in these glasses? If yes, how exactly?

Record the results of the experiments in a notebook and draw conclusions.

Popel P. P., Kriklya L. S., Chemistry: Pdruch. for 7 cells. zahalnosvit. navch. zakl. - K .: Exhibition Center "Academy", 2008. - 136 p.: il.

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