Substances and their properties. Physical and chemical phenomena

>> 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 remainder 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 grey colour. 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 absorb molecules 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 meaning.

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 grape juice, bleaching fabrics, burning various kinds 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, medicines, and other important substances. By burning fuel, people provide themselves with heat and electricity. Neutralized by chemical reactions toxic substances recycle industrial and household waste.

Certain reactions lead to negative consequences. Rusting of iron reduces the life of various mechanisms, equipment, Vehicle, 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 quantities aqueous solutions citric acid and drinking 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 to the first glass ammonia, in the second - a solution of citric acid. 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.

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?

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:

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.

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 in a glass not a large number of drinking soda.

2. Add a few drops of vinegar there (you can take lemon juice or a solution of citric acid).

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

These include those that can be observed in everyday life 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 one more example of a slow oxidative reaction of a metal in living conditions- this is the formation of a dark coating of silver sulfide Ag2S on the surface of silver products: 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 food products(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 chemical clean 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, if you are going to get rid of scale in the kettle, you can observe another example 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 soda is quenched. 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 very clear how multifaceted and interesting science chemistry. And how much benefit can be derived from understanding its laws.

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 various methods receiving 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 exhaustion natural resources of our planet, now chemists are facing 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 fuels are being developed that would be just as efficient, but would not pollute environment. To date, mankind has learned to artificially obtain various gems e.g. 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 given substance"freezes" and becomes 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 may have different shape and size. 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 at physical phenomena substances, as a rule, only change the state of aggregation, then with 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 substances: substances of natural and
  artificial origin
• Under normal conditions, substances can be in three states of aggregation
• Properties of substances that are determined by measurements or visually during
  the absence of the transformation of one substance into another, is 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 evolution of gas, precipitation, heat,
  Sveta; color change of substances
• Combustion is a complex physicochemical process of transformation of the initial
  substances into combustion products during a chemical reaction, accompanied by
  intense release of heat and light (flame)

I bet you've noticed more than once something like Mom's silver ring darkens with time. Or how a nail rusts. Or how wooden logs burn to ash. Well, okay, if mom doesn’t like silver, and you never went hiking, you saw 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.

A chemical phenomenon occurs when some substances are transformed into others: new substances have a different composition and new properties. If you also remember physics, then remember that chemical phenomena occur at the molecular and atomic level, but do not affect the composition of the nuclei of atoms.

From the point of view of chemistry, this is nothing more than a chemical reaction. And for each chemical reaction, it is necessarily possible to identify characteristic features:

• a precipitate may form during the reaction;
• the color of the substance may change;
• the consequence of the reaction may be the evolution of gas;
• heat can be released or absorbed;
• the reaction may also be accompanied by the release of light.

Also, a list of conditions necessary for a chemical reaction to occur has long been defined:

• contact: To react, the substances must come into contact.
• grinding: for the successful course of the reaction, the substances entering into it must be crushed as finely as possible, perfect option- dissolved;
• temperature: very many reactions directly depend on the temperature of substances (most often they need to be heated, but some vice versa - cooled to a certain temperature).

By writing down the equation of a chemical reaction in letters and numbers, you thereby describe the essence of a chemical phenomenon. And the law of conservation of mass is one of the most important rules in compiling such descriptions.

Chemical phenomena in nature

Of course, you understand that chemistry does not only take place in test tubes in the school laboratory. The most impressive chemical phenomena you can observe in nature. And their significance is so great that there would be no life on earth if it were not for some of the natural chemical phenomena.

So, first of all, let's talk about photosynthesis. This is the process during which plants absorb carbon dioxide from the atmosphere and under the influence of sunlight produce oxygen. We breathe this oxygen.

In general, photosynthesis proceeds in two phases, and lighting is needed for only one. Scientists conducted various experiments and found that photosynthesis proceeds even in low light. But with an increase in the amount of light, the process is greatly accelerated. It has also been observed that if the plant's light and temperature are both increased at the same time, the rate of photosynthesis increases even more. This happens up to a certain limit, after which a further increase in illumination ceases to accelerate photosynthesis.

The process of photosynthesis involves photons emitted by the sun, and special pigment molecules of plants - chlorophyll. In plant cells, it is found in chloroplasts, which is what makes the leaves green.

From a chemical point of view, photosynthesis is a chain of transformations that results in oxygen, water, and carbohydrates as an energy store.

Initially, it was believed that oxygen is formed as a result of the splitting of carbon dioxide. Later, however, Cornelius Van Niel found out that oxygen is formed as a result of the photolysis of water. Recent studies have confirmed this hypothesis.

The essence of photosynthesis can be described using the following equation: 6CO 2 + 12H 2 O + light \u003d C 6 H 12 O 6 + 6O 2 + 6H 2 O.

Breath, our with you in including, – it is also a chemical phenomenon. We inhale the oxygen produced by plants and exhale carbon dioxide.

But not only carbon dioxide is formed as a result of respiration. The main thing in this process is that due to breathing a large amount of energy is released, and this method of obtaining it is very effective.

In addition, the intermediate result of different stages of respiration is a large number of different compounds. And those, in turn, serve as the basis for the synthesis of amino acids, proteins, vitamins, fats and fatty acids.

The breathing process is complex and divided into several stages. Each of which uses a large number of enzymes that act as catalysts. The scheme of chemical reactions of respiration is almost the same in animals, plants and even bacteria.

From the point of view of chemistry, respiration is the process of oxidation of carbohydrates (as an option: proteins, fats) with the help of oxygen, as a result of the reaction, water, carbon dioxide and energy are obtained that cells store in ATP: C 6 H 12 O 6 + 6O 2 \u003d CO 2 + 6H 2 O + 2.87 * 10 6 J.

By the way, we said above that chemical reactions can be accompanied by the emission of light. In the case of breathing and the chemical reactions that go with it, this is also true. Glow (luminesce) can some microorganisms. Although the energy efficiency of breathing decreases.

Combustion also occurs with the participation of oxygen. As a result, wood (and other solid fuels) turns into ash, a substance with a completely different composition and properties. In addition, during the combustion process, a large amount of heat and light, as well as gas, is released.

Of course, not only solid substances burn, but with their help it was more convenient to give an example in this case.

From a chemical point of view, combustion is an oxidative reaction that proceeds with a very high speed. And at very, very high speed reactions may explode.

Schematically, the reaction can be written as follows: substance + O 2 → oxides + energy.

As a natural chemical phenomenon, we consider and decay.

In fact, this is the same process as combustion, only it proceeds much more slowly. Decay is the interaction of complex nitrogen-containing substances with oxygen with the participation of microorganisms. The presence of moisture is one of the factors contributing to the occurrence of decay.

As a result of chemical reactions, ammonia, volatile fatty acids, carbon dioxide, hydroxy acids, alcohols, amines, skatole, indole, hydrogen sulfide, mercaptans are formed from protein. Some of the nitrogen-containing compounds formed as a result of decay are poisonous.

If we turn again to our list of signs of a chemical reaction, we will find many of them in this case as well. In particular, there is an initial substance, a reagent, reaction products. From characteristic features note the release of heat, gases (strong-smelling), color change.

For the circulation of substances in nature, decay has a very great importance: allows you to process the proteins of dead organisms into compounds suitable for absorption by plants. And the circle starts over.

I'm sure you've noticed how easy it is to breathe in summer after a thunderstorm. And the air also becomes especially fresh and acquires a characteristic smell. Every time after a summer thunderstorm, you can observe another chemical phenomenon common in nature - ozone formation.

Ozone (O 3) in pure form is a gas of blue color. In nature, the highest concentration of ozone is in the upper atmosphere. There he acts as a shield for our planet. that protects her from solar radiation from space and does not allow the Earth to cool down, because it also absorbs its infrared radiation.

In nature, ozone is mostly formed due to the irradiation of air with the ultraviolet rays of the Sun (3O 2 + UV light → 2O 3). And also with electrical discharges of lightning during a thunderstorm.

In a thunderstorm, under the influence of lightning, part of the oxygen molecules breaks up into atoms, molecular and atomic oxygen combine, and O 3 is formed.

That is why we feel a special freshness after a thunderstorm, we breathe easier, the air seems more transparent. The fact is that ozone is a much stronger oxidizing agent than oxygen. And in a small concentration (as after a thunderstorm) is safe. And even useful, because it decomposes harmful substances in the air. In fact, it disinfects it.

However, in large doses, ozone is very dangerous for people, animals and even plants, for them it is poisonous.

By the way, the disinfecting properties of ozone obtained in the laboratory are widely used for ozonizing water, protecting products from spoilage, in medicine and cosmetology.

Of course, this is far from full list amazing chemical phenomena in nature that make life on the planet so diverse and beautiful. You can learn more about them if you look around carefully and keep your ears open. There are a lot of amazing phenomena around that are just waiting for you to become interested in them.

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: for example, brewing tea. The tea leaves heated with boiling water change their properties, as a result, the composition of water also changes: it acquires a different color, taste and properties. That is, a new substance is obtained.

If sugar is poured into the same tea, as a result of a chemical reaction, a solution will be obtained, which will again have a set of new characteristics. First of all, new, sweet, taste.

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 fuel combustion in the 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 reaction of complete combustion of fuel should look like this: C n H 2n+2 + (1.5n+0,5) O 2 = nCO 2 + (n+1) H 2 O. 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).

Plaque formation on metals as a result of oxidation (rust on iron, patina on copper, darkening of silver) - 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 Fe 2 O 3 (more precisely, Fe 2 O 3 * H 2 O). 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 + O 2 + H 2 O + CO 2 \u003d Cu 2 CO 5 H 2 (or CuCO 3 * 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 Ag 2 S 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 + 2H 2 S + O 2 = 2Ag 2 S + 2H 2 O.

Let's go back to the kitchen. Here you can consider a few more interesting chemical phenomena: scale formation in the kettle 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 undergo decomposition into carbon dioxide and an insoluble precipitate (CaCO 3 andmgCO 3). 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: NaHCO 3 + CH 3 COOH=CH 3 COONa + H 2 O + CO 2 . 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 soda is quenched. 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.

Among the many, many phenomena invented by nature and man, there are special ones that are difficult to describe and explain. They also include burning 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 burning of water is a chemical phenomenon, at 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, he achieves high temperature combustion (more than one and a half thousand degrees), plus water is formed again 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 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 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 CaCO 3. The basis for its formation are wastewater, natural limestone, and the stalactite itself is built due to the precipitation of calcium carbonate (downward growth) and the adhesion force of atoms in 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 get a name stalagnates.

Conclusion

Many amazing, beautiful, as well as dangerous and frightening chemical phenomena occur in the world every day. From many, man has learned to benefit: creates Construction Materials, prepares food, makes vehicles travel long distances and much more.

Without many chemical phenomena, the existence of life on earth would not have been possible: without the ozone layer, people, animals, plants would not have survived 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.

blog.site, with full or partial copying of the material, a link to the source is required.