Chemical phenomena inside and around us. Examples of physical phenomena and their descriptions

Keywords abstract: Physical phenomena, chemical phenomena, chemical reactions, signs of chemical reactions, the meaning of physical and chemical phenomena.

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

Chemical phenomena- these are phenomena as a result of which other substances are formed from given substances. In chemical phenomena, starting substances are transformed into other substances that have different properties. Examples of chemical phenomena - fuel combustion, rotting organic matter, rusting of iron, souring of milk.

Chemical phenomena are also called chemical reactions.

Conditions for the occurrence of chemical reactions

The fact that during chemical reactions some substances are converted into others can be judged by external signs : release of heat (sometimes light), change in color, appearance of odor, formation of sediment, release of gas.

For many chemical reactions to begin, it is necessary to bring them into close contact of reacting substances . To do this, they are crushed and mixed; The contact area of ​​the reacting substances increases. The finest crushing of substances occurs when they dissolve, so many reactions are carried out in solutions.

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

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

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

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

The meaning of physical and chemical phenomena

Chemical reactions are of great importance. They are used to produce metals, plastics, mineral fertilizers, medicines, etc., and also serve as a source various types energy. Thus, when fuel burns, heat is released, which is used in everyday life and in industry.

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

>> Physical and chemical phenomena (chemical reactions). Let's experiment at home. External effects in chemical reactions

Physical and chemical phenomena (chemical reactions)

The material in this paragraph will help you figure out:

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

In natural history lessons, 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, so they are one substance (in different states of aggregation).

Phenomena in which a substance does not transform into another are called physical.

Physical phenomena include not only changes in 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, and 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. Let's consider the process of burning alcohol (Fig. 46). It occurs with the participation of oxygen contained in the air. When burned, alcohol seemingly turns into a gaseous state, just as water turns into steam when heated. But that's not true. If the gas obtained as a result of the combustion of alcohol is cooled, then part of it will condense into liquid, but not into alcohol, but into water. The rest of the gas will remain. With the help of additional experiment it can be proven that this residue is carbon dioxide.

Rice. 46. ​​Burning alcohol

So the alcohol that burns and oxygen, which participates in the combustion process, are converted into water and carbon dioxide.

Phenomena in which some substances are transformed into others are called chemical phenomena or chemical reactions.

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

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

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 disintegrate into atoms, which, when combined, form 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 interaction of substances are also known.

External effects accompanying chemical reactions.

By observing chemical reactions, the following effects can be recorded:

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

Rice. 47. Some external effects during chemical reactions: a - appearance
coloring; b - gas release; c - appearance of sediment

Laboratory experiment No. 3

The appearance of color as a result of the reaction

Are solutions of soda ash and phenolphthalein colored?

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

Laboratory experiment No. 4

Release of gas as a result of the reaction

Add a little chloride acid to the soda ash solution. What are you observing?

Laboratory experiment No. 5

The appearance of a precipitate as a result of the reaction

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

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

Example 1. Silver powder obtained in a test tube as a result of a chemical reaction has grey colour. If you melt it and then cool the melt, you will get a piece of metal, but not gray, but white, with a characteristic shine.

Example 2. If you heat natural water, gas bubbles will begin to emerge from it long before boiling. This is dissolved air; its solubility in water decreases when heated.

Example 3. An unpleasant odor in the refrigerator disappears if granules of silica gel, one of the silicon compounds, are placed in it. Silica gel absorbs molecules of various substances without destroying them. Activated carbon works in a similar way in a gas mask.

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

To determine what kind of transformation has occurred - physical or chemical, you 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 occur constantly in nature. Substances dissolved in rivers, seas, and oceans interact with each other, some react with oxygen. Plants absorb carbon dioxide from the atmosphere, water and dissolved substances from the soil and process them into proteins, fats, glucose, starch, vitamins, other compounds, as well as oxygen.

This is interesting

As a result of photosynthesis, about 300 billion tons of carbon dioxide are absorbed from the atmosphere each year, 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 frying of meat, vegetables, baking bread, souring of milk, fermentation of grape juice, bleaching of fabrics, burning of various types of fuel, hardening of cement and alabaster, blackening over time silver jewelry and so on.

Chemical reactions form the basis of such technological processes as the extraction 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. Using chemical reactions, they neutralize toxic substances and process industrial and household waste.

The occurrence of some reactions leads to negative consequences. Rusting of iron shortens the life of various mechanisms, equipment, Vehicle, leads to large losses of this metal. Fires destroy housing, industrial and cultural sites, 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 the phenomena in which each substance is conserved.

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

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

?
100. Match:

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

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

102. Why do you think alone 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 baking soda. Pour portions of both solutions together into a separate glass. What's happening?

Add a few soda crystals to the remainder of the citric acid solution, and a few citric acid crystals to the remainder 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 brilliant green alcohol solution, known as “zelenka,” to each. Add a few drops of ammonia to the first glass, and citric acid solution to the second. Has the color of the dye (green) in these glasses changed? If so, how exactly?

Write down the results of the experiments in a notebook and draw conclusions.

Popel P. P., Kryklya L. S., Chemistry: Pidruch. for 7th grade zagalnosvit. navch. closing - K.: VC "Academy", 2008. - 136 p.: ill.

Lesson objectives.

Educational: based on students’ knowledge from the natural history course and a computer presentation, concretize students’ knowledge about physical and chemical phenomena, using examples to identify their differences; Based on the life experience of students, introduce them to the signs of chemical reactions and the conditions for their occurrence and course.

Developmental: to promote the development of students’ creative thinking, the ability to establish cause-and-effect relationships, the dependence of the flow of chemical reactions on external conditions, to develop general educational and practical skills when observing and performing a chemical experiment.

Educational: to form students’ scientific worldview and interest in the subject.

Lesson type: learning a new topic.

Methods: verbal-visual, practical, partially search, working with a textbook.

Forms of organization of cognitive activity: frontal, group, individual.

Students must:

know: definition of physical and chemical phenomena, signs and conditions for the flow of chemical reactions, the significance of physical and chemical phenomena in human life.

be able to: distinguish between physical and chemical phenomena, apply knowledge about physical and chemical phenomena in practice.

Equipment: computer, multimedia projector, presentation.

On the teacher's desk.

1. A mixture of iron and sulfur powders, test tube, alcohol lamp, tripod.

On the students' desks.

1. A tripod, a flask of water closed with a stopper with a gas outlet tube, a beaker, a glass plate, an alcohol lamp.
2. Iron filings, sulfur powder, filter paper, magnet, cylinder of water.

During the classes

I. Organizational stage

Teacher greeting students.

Checking the readiness of students and their workplaces for the lesson.

II. Communicating the topic and objectives of the lesson

In natural history lessons, you gained initial knowledge about phenomena occurring in nature. Today in the lesson you will expand your knowledge about physical and chemical phenomena, learn to distinguish them from each other, get acquainted with the signs and conditions of chemical reactions and their significance in human life (slide No. 1) .

III. Learning a new topic

Plan for studying a new topic:

1. Phenomena occurring in nature. Classification of phenomena.

2. Physical phenomena.

• Laboratory experiment “Water evaporation and steam condensation”.

3. Chemical phenomena.

• Laboratory experiment “Studying the properties of iron and sulfur.”
• Demonstration experiment “Heating a mixture of iron and sulfur. Study of the properties of the resulting substance.”

4. Signs of chemical reactions. Demonstration of a video clip.

5. Conditions for the occurrence and course of chemical reactions (student message).

6. The meaning of physical phenomena and chemical reactions.

1. Phenomena occurring in nature. Classification of phenomena

Teacher: Guys, what surrounds us? (slide number 2)

Student: Nature. Inanimate and alive.

Teacher: Changes constantly occur in nature. Give examples.

Day turns to night (slide number 3)

It rains or snows, water evaporates (slide number 4)

The grass is green, the stream is flowing (slide number 5)

The wind is blowing, the fire is burning (slide number 6)

A man prepares food. (slide number 7)

Teacher: What can you call these changes?

Student: All changes occurring in nature are called natural phenomena.

Teacher: How are all natural phenomena classified?

Student: Natural phenomena can be biological, physical and chemical (slide number 8). Let's get acquainted with physical and chemical phenomena.

2. Physical phenomena

Teacher: What phenomena are called physical?

Student: Phenomena in which there is no transformation of one substance into another are called physical. For example: wax melting, water evaporating, ice melting (slide number 9).

Laboratory experience
“Evaporation of water and condensation of steam”

Teacher: Let’s conduct the experiment “Evaporation of water and condensation of steam.” Assemble the device as shown on the slide (slide number 10) , check its tightness. Observing safety precautions when working with an alcohol lamp and glassware, light the alcohol lamp and heat the flask with water.

What are you observing?

Student: When liquid water boils, it turns into a gaseous state (water vapor). When water vapor hits a glass plate, it condenses into water droplets.

Teacher: What is the essence of physical phenomena?

Student: During physical phenomena, the state of aggregation and form of matter changes (slide number 11).

3. Chemical phenomena

Teacher: Chemical phenomena are a completely different matter. Burning fire, souring milk, rusting iron and steel products (slide number 12).

What happens during chemical events?

Student: During chemical phenomena, some substances are transformed into others.

Teacher: Let's do it experiment “Studying the properties of sulfur and iron” according to plan (slide number 13). Determine the color of the substances.

Teacher: Do the properties of substances in a mixture change?

Student: No. The substances included in the mixture retain their individual properties.

Teacher: Let's heat the resulting mixture of sulfur and iron (slide number 15). Let's take a mixture of sulfur and iron and heat it in a test tube.

What are you observing?

Student: The mixture began to darken, then became red hot.

Teacher: Let’s extract from the test tube what is formed after the reaction and study its properties (color, relationship to water and magnet). To do this, grind the resulting substance and apply a magnet to it.

What are you observing?

Student: Powder is not attracted by a magnet.

Teacher: Let’s put the resulting substance in water.

What are you observing?

Student: The substance sinks and is not separated into sulfur and iron.

Teacher: What happened when the mixture of sulfur and iron was heated?

Student: When a mixture of sulfur and iron was heated, a new substance was formed, which in its properties differs from the properties of the original substances (slide number 16).

Teacher: Chemical phenomena are called chemical reactions.

4. Signs of chemical reactions

Teacher: The fact that a chemical reaction has occurred can be judged by its signs. Watch a video demonstrating the experience (slide number 17).

What signs of chemical reactions did you observe during the demonstration experiments?

Student: We observed such signs of chemical reactions as changes in color, precipitation, release of gas, release of energy.

Teacher: On the next slide (slide number 18) shows all the signs that can be observed during chemical reactions.

Teacher: For a chemical reaction to begin, certain conditions are necessary.

Student message (slide number 19)

6. The meaning of physical phenomena and chemical reactions

Teacher: Study the text of paragraph §3 “The significance of physical phenomena and chemical reactions”, fill in table:

The meaning of physical phenomena and chemical reactions

IV. Consolidation

Frontal survey (slide number 21)

1, 2. Identify physical and chemical phenomena (slides No. 22, 23)

3. Phenomena in which the shape and state of aggregation of a substance changes are called... (slide number 24)

A – chemical

B – physical

B – biological

4. Phenomena in which the transformation of one substance into another occurs is called ... (slide number 25)

A – physical

B – chemical

B – biological

5. Physical phenomena include: (slide number 26)

A – glass melting

B – wood burning

B – evaporation of water

G – sour milk

D – dissolution of salt in water

E – rotten eggs

6. Chemical phenomena include: (slide number 27)

A – rusting of iron

B – fog formation

B – fruit rotting

G – wax melting

D – burning of kerosene

E – water evaporation

7. Indicate a sign of a chemical reaction when an acid acts on soda: (slide number 28)

A – formation of sediment

B – color change

B – gas evolution

8. Indicate a sign of a chemical reaction when iron rusts: (slide number 29)

A – gas evolution

B – formation of sediment

B – color change

9. Indicate a sign of a chemical reaction when wood burns: (slide number 30)

A – color change

B – precipitation

B – heat release

V. Summing up the lesson, grading

VI. Homework

Literature

1. Alikberova L.Yu. Entertaining chemistry: A book for students, teachers, parents. – M.: Ast-Press, 1999.
2. Rudzites G.E., Feldman F.G. Chemistry. 8th grade: Textbook for general education - M.: Enlightenment, 2007.
3. Khripkova A.G. and others. Natural science: textbook for 7th grade of general education institutions. – M.: Education, 2005.
4. http://chemistry.r2.ru/
5. http://www.chem.msu.su/rus/elibrary/
6. CD disc “ Great encyclopedia Cyril and Methodius 2009.” – Cyril and Methodius LLC, 2009.
7. CD “General and Inorganic Chemistry”: In-depth course on general and inorganic chemistry. – Laboratory of Multimedia Systems, MarSTU, 2001.

Since ancient times, people have been collecting information about the world in which they live. There was only one science that united all the information about nature that humanity had accumulated at that time. At that time, people did not yet know that they were observing examples of physical phenomena. Currently, this science is called “natural science”.

What does physical science study?

Over time, scientific ideas about the world around us have changed noticeably - there are many more of them. Natural science split into many separate sciences, including: biology, chemistry, astronomy, geography and others. In a number of these sciences there is no last place takes up physics. Discoveries and achievements in this field have allowed humanity to acquire new knowledge. These include the structure and behavior of various objects of all sizes (from giant stars to the smallest particles - atoms and molecules).

The physical body is...

There is a special term “matter”, which in scientific circles is used to describe everything that is around us. A physical body consisting of matter is any substance that occupies a certain place in space. Any physical body in action can be called an example of a physical phenomenon. Based on this definition, we can say that any object is a physical body. Examples of physical bodies: button, notepad, chandelier, cornice, Moon, boy, clouds.

What is a physical phenomenon

Any matter is in constant change. Some bodies move, others come into contact with others, and others rotate. It is not for nothing that many years ago the philosopher Heraclitus uttered the phrase “Everything flows, everything changes.” Scientists even have a special term for such changes - these are all phenomena.

Physical phenomena include everything that moves.

What types of physical phenomena are there?

• Thermal.

These are phenomena when, due to the effects of temperature, some bodies begin to transform (shape, size and condition change). An example of physical phenomena: under the influence of the warm spring sun, icicles melt and turn into liquid; with the onset of cold weather, puddles freeze, boiling water becomes steam.

• Mechanical.

These phenomena characterize a change in the position of one body in relation to the others. Examples: a clock is running, a ball is jumping, a tree is shaking, a pen is writing, water is flowing. They are all in motion.

• Electrical.

The nature of these phenomena fully justifies their name. The word "electricity" has its roots in Greek language, where "electron" means "amber". The example is quite simple and probably familiar to many. When you suddenly take off a woolen sweater, you hear a small crack. If you do this by turning off the light in the room, you can see sparkles.

• Light.

A body participating in a phenomenon associated with light is called luminous. As an example of physical phenomena, we can give everyone famous star our solar system- The sun, as well as any other star, lamp, and even a firefly.

• Sound.

Sound propagation, behavior sound waves in collisions with an obstacle, as well as other phenomena that are in one way or another related to sound, belong to this type of physical phenomena.

• Optical.

They happen thanks to light. For example, humans and animals are able to see because there is light. This group also includes the phenomena of propagation and refraction of light, its reflection from objects and passage through different media.

Now you know what physical phenomena are. However, it is worth understanding that there is a certain difference between natural and physical phenomena. Yes, when natural phenomenon Several physical phenomena occur simultaneously. For example, when lightning strikes the ground, the following effects occur: sound, electrical, thermal and light.

Everything that surrounds us: both living and inanimate nature, is in constant motion and is constantly changing: planets and stars move, it rains, trees grow. And a person, as is known from biology, constantly goes through some stages of development. Grinding grains into flour, falling a stone, boiling water, lightning, glowing a light bulb, dissolving sugar in tea, moving vehicles, lightning, rainbows are examples of physical phenomena.

And with substances (iron, water, air, salt, etc.) various changes or phenomena occur. The substance can be crystallized, melted, crushed, dissolved and again isolated from solution. However, its composition will remain the same.

So, granulated sugar can be crushed into a powder so fine that the slightest breath will cause it to rise into the air like dust. Sugar grains can only be seen under a microscope. Sugar can be divided into even smaller parts by dissolving it in water. If you evaporate water from a sugar solution, the sugar molecules again combine with each other to form crystals. But even when dissolved in water or when crushed, sugar remains sugar.

In nature, water forms rivers and seas, clouds and glaciers. When water evaporates, it turns into steam. Water vapor is water in a gaseous state. When exposed to low temperatures (below 0˚C), water turns into a solid state - turns into ice. The smallest particle of water is a water molecule. A water molecule is also the smallest particle of steam or ice. Water, ice and steam are not different substances, but the same substance (water) in different states of aggregation.

Like water, other substances can be transferred from one state of aggregation to another.

When characterizing a substance as a gas, liquid or solid, we mean the state of the substance under normal conditions. Any metal can not only be melted (transformed into a liquid state), but also turned into gas. But this requires very high temperatures. In the outer shell of the Sun, metals are in a gaseous state, because the temperature there is 6000˚C. And, for example, carbon dioxide can be converted into “dry ice” by cooling.

Phenomena in which there is no transformation of one substance into another are classified as physical phenomena. Physical phenomena can lead to a change, for example, in the state of aggregation or temperature, but the composition of the substances will remain the same.

All physical phenomena can be divided into several groups.

Mechanical phenomena are phenomena that occur with physical bodies when they move relative to each other (the revolution of the Earth around the Sun, the movement of cars, the flight of a parachutist).

Electrical phenomena are phenomena that occur during the appearance, existence, movement and interaction of electric charges (electricity, telegraphy, lightning during a thunderstorm).

Magnetic phenomena are phenomena associated with the occurrence of magnetic properties(attraction of iron objects by a magnet, turning the compass needle to the north).

Optical phenomena are phenomena that occur during the propagation, refraction and reflection of light (rainbows, mirages, reflection of light from a mirror, the appearance of shadows).

Thermal phenomena are phenomena that occur during heating and cooling of physical bodies (melting snow, boiling water, fog, freezing of water).

Atomic phenomena are phenomena that occur when internal structure substances of physical bodies (glow of the Sun and stars, atomic explosion).

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