Chemical phenomena in everyday life. 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 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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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.

1. Close contact of the reactants (necessary): H 2 SO 4 + Zn = ZnSO 4 + H 2 2. Heating (possible) a) to start the reaction b) constantly Classification of chemical reactions according to various criteria 1. By the presence of a phase boundary, all chemical reactions are divided into homogeneous and heterogeneous A chemical reaction occurring within the same phase is called homogeneous chemical reaction. The chemical reaction that occurs at the interface is called heterogeneous chemical reaction. In a multi-step chemical reaction, some steps may be homogeneous while others may be heterogeneous. Such reactions are called homogeneous-heterogeneous. Depending on the number of phases that form the starting substances and reaction products, chemical processes can be homophasic (the starting substances and products are within the same phase) and heterophase (the starting substances and products form several phases). The homo- and heterophasic nature of a reaction is unrelated to whether the reaction is homo- or heterogeneous. Therefore, four types of processes can be distinguished: Homogeneous reactions (homophasic). In reactions of this type, the reaction mixture is homogeneous, and the reactants and products belong to the same phase. An example of such reactions are ion exchange reactions, for example, neutralization of an acid solution with an alkali solution: Heterogeneous homophasic reactions. The components are within the same phase, however, the reaction proceeds at the phase boundary, for example, on the surface of the catalyst. An example would be the hydrogenation of ethylene on a nickel catalyst: Homogeneous heterophase reactions. The reactants and products in such a reaction exist within several phases, but the reaction proceeds in one phase. Thus, the oxidation of hydrocarbons in the liquid phase with gaseous oxygen can take place. Heterogeneous heterophase reactions. In this case, the reactants are in a different phase state, the reaction products can also be in any phase state. The reaction process takes place at the phase boundary. An example is the reaction of salts of carbonic acid (carbonates) with Bronsted acids: 2. By changing the oxidation states of the reagents[edit | edit wiki text] In this case, redox reactions are distinguished, in which the atoms of one element (oxidizing agent) are recovering , that is, they lower their oxidation state, and the atoms of another element (reducing agent) are oxidized , that is, they increase their oxidation state. A special case of redox reactions are the proportionate reactions, in which the oxidizing and reducing agents are atoms of the same element in different oxidation states. An example of a redox reaction is the combustion of hydrogen (reductant) in oxygen (oxidizer) to form water: An example of a coproportionation reaction is the decomposition of ammonium nitrate when heated. In this case, nitrogen (+5) of the nitro group acts as an oxidizing agent, and nitrogen (-3) of the ammonium cation acts as a reducing agent: They do not belong to redox reactions in which there is no change in the oxidation states of atoms, for example: 3. According to the thermal effect of the reaction All chemical reactions are accompanied by the release or absorption of energy. When chemical bonds are broken in the reactants, energy is released, which is mainly used to form new chemical bonds. In some reactions, the energies of these processes are close, and in this case the total thermal effect of the reaction approaches zero. In other cases, we can distinguish: exothermic reactions that go with the release of heat (positive thermal effect) CH 4 + 2O 2 \u003d CO 2 + 2H 2 O + energy (light, heat); CaO + H 2 O \u003d Ca (OH) 2 + energy (heat). endothermic reactions during which heat is absorbed (negative thermal effect) from the environment. Ca (OH) 2 + energy (heat) \u003d CaO + H 2 O The heat effect of the reaction (reaction enthalpy, Δ r H), which is often very important, can be calculated according to Hess's law if the enthalpies of formation of reactants and products are known. When the sum of the enthalpies of the products is less than the sum of the enthalpies of the reactants (Δ r H< 0) наблюдается выделение тепла, в противном случае (Δ r H >0) - absorption. 4. According to the type of transformations of reacting particles[edit | edit wiki text] compounds: decompositions: substitutions: exchanges (including the type of reaction-neutralization): Chemical reactions are always accompanied by physical effects: the absorption or release of energy, a change in the color of the reaction mixture, etc. It is these physical effects that are often judged about the course of chemical reactions. Connection reaction- a chemical reaction, as a result of which only one new substance is formed from two or more initial substances. Both simple and complex substances can enter into such reactions. decomposition reaction A chemical reaction that produces several new substances from one substance. Only complex compounds enter into reactions of this type, and their products can be both complex and simple substances. substitution reaction- a chemical reaction in which the atoms of one element, which are part of a simple substance, replace the atoms of another element in its complex compound. As follows from the definition, in such reactions one of the starting materials must be simple and the other complex. Exchange reactions- a reaction, as a result of which two complex substances exchange their constituent parts 5. According to the direction of flow, chemical reactions are divided into irreversible and reversible irreversible refers to chemical reactions that proceed in only one direction. from left to right"), as a result of which the starting substances are converted into reaction products. Such chemical processes are said to proceed "to the end." These include combustion reactions, as well as reactions accompanied by the formation of poorly soluble or gaseous substances reversible called chemical reactions occurring simultaneously in two opposite directions ("from left to right" and "from right to left"). In the equations of such reactions, the equal sign is replaced by two oppositely directed arrows. Among two simultaneously occurring reactions, there are direct( flows from left to right) and reverse(flows "from right to left"). Since in the course of a reversible reaction the starting materials are both consumed and formed, they are not completely converted into reaction products. Therefore, reversible reactions are said to proceed "not to the end." As a result, a mixture of initial substances and reaction products is always formed. 6. On the basis of the participation of catalysts, chemical reactions are divided into catalytic and non-catalytic Catalytic 2SO 2 + O 2 → 2SO 3 (catalyst V 2 O 5) are called reactions occurring in the presence of catalysts. In the equations of such reactions, the chemical formula of the catalyst is indicated above the equal sign or reversibility, sometimes together with the designation of the flow conditions. Reactions of this type include many reactions of decomposition and combination. Non-catalytic 2NO + O2 \u003d 2NO 2 are many reactions that occur in the absence of catalysts. These are, for example, exchange and substitution reactions.

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 come across many substances. Among them are water, iron, aluminum, plastic, soda, salt and many others.

Substances that exist in nature, such as oxygen and nitrogen contained in the air, substances dissolved in water, and having a natural origin, are called natural substances.

Aluminum, zinc, acetone, lime, soap, aspirin, polyethylene and many other substances do not exist in nature. They are obtained in the laboratory and produced by the industry. Artificial substances do not occur in nature, they are created from natural substances.

Some substances that exist in nature can also be obtained in a chemical laboratory. So, when potassium permanganate is heated, oxygen is released, and when chalk is heated - carbon dioxide. Scientists have learned how to turn graphite into diamond, grow crystals of ruby, sapphire and malachite.

So, along with substances of natural origin, there is a huge variety of artificially created substances that are not found in nature. Substances that are not found in nature are produced at various enterprises: factories, plants, combines, etc.

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

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

Aggregate state of matter

Substances can exist in several states of aggregation, three of which you know: solid, liquid, gaseous. For example, water in nature exists in all three states of aggregation: solid (in the form of ice and snow), liquid (liquid water) and gaseous (water vapor).

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

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

physical phenomena. Physical properties of substances.

Phenomena in which substances change the state of aggregation, but do not turn into other substances, are called physical.

Each individual substance has certain properties. The properties of substances can be different or similar to each other. Each substance is described using a set of physical and chemical properties.

Let's take water as an example. Water freezes and turns into ice at a temperature of 0°C, and boils and turns into steam at a temperature of +100°C. These phenomena are physical, since water has not turned into other substances, only a change in the state of aggregation occurs. These freezing and boiling points are physical properties specific to water.

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

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

The main physical properties of substances include the following: state of aggregation, color, odor, solubility in water, density, boiling point, melting point, thermal conductivity, electrical conductivity.

Such physical properties as color, smell, taste, shape of crystals can be determined visually, using the senses, and density, electrical conductivity, melting and boiling points are determined by measurement. Information about the physical properties of many substances is collected in special literature, for example, in reference books.

The physical properties of a substance depend on its state of aggregation. For example, the density of ice, water and water vapor is different. Gaseous oxygen is colorless, and liquid oxygen is blue.

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

As an example, we characterize the physical properties of water:

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

Crystalline and amorphous substances

When describing the physical properties of solids, it is customary to describe the structure of the substance. If you look at a sample of table salt under a magnifying glass, you will notice that the salt consists of many tiny crystals. Very large crystals can also be found in salt deposits.

Crystals are solid bodies that have the shape of regular polyhedra.

Crystals can be of various shapes and sizes. Crystals of certain substances, such as table salt – fragile, easy to break. There are crystals quite hard. For example, one of the hardest minerals is diamond.

If you look at salt crystals under a microscope, you will notice that they all have a similar structure. If we consider, for example, glass particles, then they will all have a different structure - such substances are called amorphous. Amorphous substances include glass, starch, amber, beeswax.

Amorphous substances - substances that do not have a crystalline structure

chemical phenomena. Chemical reaction.

If, in physical phenomena, substances, as a rule, only change the state of aggregation, then in chemical phenomena, some substances are transformed into other substances.

Here are some simple examples: the burning of a match is accompanied by charring of wood and the release of gaseous substances, that is, an irreversible transformation of wood into other substances occurs.

Another example: over time, bronze sculptures become covered with a green coating. This is because bronze contains copper. This metal slowly interacts with oxygen, carbon dioxide and air moisture, as a result, new green substances are formed on the surface of the sculpture.

Chemical phenomena - the phenomena of the transformation of one substance into another

The process of interaction of substances with the formation of new substances is called a chemical reaction. Chemical reactions take place all around us. Chemical reactions take place in ourselves. In our body, transformations of many substances are constantly taking place, substances react with each other, forming reaction products. Thus, in a chemical reaction there are always reacting substances, and substances formed as a result of the reaction.

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

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

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: natural substances 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)

Publication date 01/08/2013 18:41

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 of chemical phenomena

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.

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

Conditions for the occurrence and course of chemical phenomena

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 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.

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