1. Close contact of the reacting substances (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 one phase is called homogeneous chemical reaction. The chemical reaction occurring 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 materials and reaction products, chemical processes can be homophasic (starting substances and products are within one phase) and heterophasic (starting substances and products form several phases). Homo- and heterophasicity of a reaction is not related to whether the reaction is homo- or heterogeneous. Therefore, four types of processes can be distinguished: Homogeneous reactions (homophasic). In this type of reaction, the reaction mixture is homogeneous and the reactants and products belong to the same phase. An example of such reactions is ion exchange reactions, for example, neutralization of an acid solution with an alkali solution: Heterogeneous homophasic reactions. The components are within one phase, but the reaction occurs at the phase boundary, for example, on the surface of the catalyst. An example would be the hydrogenation of ethylene over a nickel catalyst: Homogeneous heterophasic reactions. The reactants and products in such a reaction exist within several phases, but the reaction occurs in a single phase. This is how the oxidation of hydrocarbons in the liquid phase with gaseous oxygen can take place. Heterogeneous heterophasic reactions. In this case, the reactants are in different phase states, and the reaction products can also be in any phase state. The reaction process occurs at the phase boundary. An example is the reaction of carbonic acid salts (carbonates) with Bronsted acids: 2. By changing the oxidation states of the reactants[edit | edit wiki text] In this case, a distinction is made between redox reactions, in which atoms of one element (oxidizing agent) are being restored , that is, they lower their oxidation state, and the atoms of another element (reducing agent) oxidize , that is, they increase their oxidation state. A special case of redox reactions are proportionation reactions, in which the oxidizing and reducing agents are atoms of the same element located in different degrees oxidation. An example of a redox reaction is the combustion of hydrogen (a reducing agent) in oxygen (an oxidizing agent) to form water: An example of a comporportionation reaction is the decomposition reaction of ammonium nitrate when heated. In this case, the oxidizing agent is nitrogen (+5) of the nitro group, and the reducing agent is nitrogen (-3) of the ammonium cation: 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 breaking chemical bonds The reagents release energy, which is mainly used to form new chemical bonds. In some reactions the energies of these processes are close, and in this case the overall thermal effect of the reaction approaches zero. In other cases, we can distinguish: exothermic reactions that occur with the release of heat (positive thermal effect) CH 4 + 2O 2 = CO 2 + 2H 2 O + energy (light, heat); CaO + H 2 O = Ca (OH) 2 + energy (heat). endothermic reactions during which heat is absorbed (negative thermal effect) from the environment. Ca(OH) 2 + energy (heat) = CaO + H 2 O The thermal effect of a reaction (reaction enthalpy, Δ r H), which is often very important, can be calculated using Hess’s law if the enthalpies of formation of the 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. By type of transformation of reacting particles[edit | edit wiki text] compounds: decomposition: substitution: exchange (including the type of reaction - neutralization): Chemical reactions are always accompanied by physical effects: absorption or release of energy, change in the color of the reaction mixture, etc. It is by these physical effects that people are often judged about the occurrence of chemical reactions. Compound reaction-a chemical reaction that results in one or more more starting substances, only one new one is formed. Both simple and complex substances can enter into such reactions. Decomposition reaction-a chemical reaction that results in the formation of several new substances from one substance. Reactions of this type involve only complex compounds, and their products can be both complex and simple substances Substitution reaction-a chemical reaction as a result of which the atoms of one element included in the composition simple substance, replace atoms of another element in its complex compound. As follows from the definition, in such reactions one of the starting substances must be simple and the other complex. Exchange reactions- a reaction that results in two complex substances exchange their components 5. Based on the direction of occurrence, chemical reactions are divided into irreversible and reversible Irreversible chemical reactions that proceed in only one direction are called from left to right"), as a result of which the starting substances are transformed into reaction products. Such chemical processes are said to proceed “to the end.” These include combustion reactions, and also reactions accompanied by the formation of poorly soluble or gaseous substances Reversible are chemical reactions that occur 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, they are distinguished straight( flows from left to right) and reverse(proceeds “from right to left”). Since during a reversible reaction the starting substances are simultaneously consumed and formed, they are not completely converted into reaction products. Therefore, reversible reactions are said to proceed “not completely.” As a result, a mixture of starting substances and reaction products is always formed. 6. Based on 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 reactions that occur in the presence of catalysts. In the equations of such reactions chemical formula the catalyst is indicated above the equals or reversibility sign, sometimes together with the designation of the conditions of occurrence. Reactions of this type include many decomposition and combination reactions. Non-catalytic 2NO+O2=2NO 2 refers to many reactions that occur in the absence of catalysts. These are, for example, exchange and substitution reactions.

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.Copper wire length changes in summer and winter: increases with heating and decreases with cooling.

3.Volume air in the balloon increases in a warm room.

Changes in substances occurred, but water remained water, copper remained copper, air remained air.

New substances, despite their changes, were not formed.

Experience

1. Close the test tube with a stopper with a tube inserted into it

2. Place the end of the tube in a glass of water. We heat the test tube with our hands. The volume of air in it increases, and some of the air from the test tube escapes into a glass of water (air bubbles are released).

3. As the test tube cools, the volume of air decreases and water enters the test tube.

Conclusion. Changes in air volume are a physical phenomenon.

Quests

Give 1–2 examples of changes occurring in substances that can be called a physical phenomenon. Write examples in your notebook.

Chemical phenomenon (reaction) – a phenomenon in which new substances are formed.

What signs can be used to determine what happened? chemical reaction ? Some chemical reactions cause precipitation. 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 examples of such reactions in the table.

Signs of chemical reactions
Change in color of the original substance	Change in taste of the original substance	Precipitation	Gas release	Odor appears

Reaction	Sign
	Color change
	Change in taste
	Gas release

In live and inanimate nature Various chemical reactions are constantly taking place. Our body is also a real factory of chemical transformations of one substance into another.

Let's observe some chemical reactions.

You cannot conduct experiments with fire yourself!!!

Experience 1

Let's hold a piece of white bread containing organic matter over the fire.

We observe:

1. charring, that is, color change;

2. appearance of odor.

Conclusion . A chemical phenomenon has occurred (a new substance has been formed - coal)

Experience 2

Let's prepare a glass of starch. Add a little water and mix. Then drop a drop of iodine solution.

We observe a sign of a reaction: color change (blue discoloration of starch)

Conclusion. A chemical reaction has occurred. The starch has turned into another substance.

Experience 3

1. Dissolve in a glass small quantity baking soda.

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

We observe the release of gas bubbles.

Conclusion. The release of gas is one of the signs of a chemical reaction.

Some chemical reactions are accompanied by the release of heat.

Quests

Place a few pieces of raw potatoes in a glass jar (or glass). Add hydrogen peroxide from your home medicine cabinet. Explain how you can determine that a chemical reaction has occurred.

The world around us, with all its richness and diversity, lives according to laws that are quite easy to explain with the help of sciences such as physics and chemistry. And even the basis of the life activity of such a complex organism as a person is nothing more than chemical phenomena and processes.

Definitions and examples

An elementary example is a kettle put on fire. After some time, the water will begin to heat up and then boil. We will hear a characteristic hissing sound, and streams of steam will fly out of the neck of the kettle. Where did it come from, because it wasn’t originally in the dishes! Yes, but water, at a certain temperature, begins to turn into gas, changes its physical condition from liquid to gaseous. Those. it remained the same water, only now in the form of steam. This

And we will see chemical phenomena if we put a bag of tea leaves into boiling water. Water in a glass or other vessel will turn red red-brown color. A chemical reaction will occur: under the influence of heat, the tea leaves will begin to steam, releasing the color pigments and flavor properties inherent in this plant. We will get a new substance - a drink with specific qualitative characteristics characteristic only of it. If we add a few spoons 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, the reaction will not occur, the tea leaves and water will not interact, and the sugar will not want to dissolve either.

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

Physical phenomena are those in which chemical composition the 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 of occurrence and occurrence

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

• as a result or during its occurrence, a precipitate occurs;
• the color of the substance changes;
• Gases, such as carbon monoxide, may be released during combustion;
• heat is absorbed or, conversely, released;
• light emission is possible.

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

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

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

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

Description physical processes and phenomena occurs through physical formulas and the solution of physical problems.

>> 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 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. Let's consider the process of burning alcohol (Fig. 46). It occurs with the participation of oxygen contained in the air. When burned, alcohol appears to transform 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 it is created high temperature. 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, you can record the following effects:

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, that is, it indicates a chemical phenomenon. Other external effects can also be observed during physical events. Let's give a few examples.

Example 1. Silver powder obtained in a test tube as a result of a chemical reaction has gray. 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 heated natural water, then gas bubbles will begin to emerge from it long before boiling. This is dissolved air; its solubility in water decreases when heated.

Example 3. The unpleasant odor in the refrigerator disappears if granules of silica gel, one of the silicon compounds, are placed in it. Silica gel absorbs molecules 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

Due to photosynthesis, about 300 billion tons are absorbed from the atmosphere annually carbon dioxide, 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 frying meat, vegetables, baking bread, souring milk, fermenting grape juice, bleaching fabrics, burning various types fuel, hardening of cement and alabaster, blackening of silver jewelry over time, etc.

Chemical reactions form the basis of such technological processes such 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, process industrial and household waste.

Some reactions lead to negative consequences. Rusting of iron shortens the life of various mechanisms, equipment, vehicles, leads to big losses this metal. Fires destroy housing, industrial and cultural facilities, and historical values. Most foods spoil due to their interaction with oxygen in the air; in this case, substances are formed that have bad smell, 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 may 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 amounts of aqueous solutions of 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 content lesson outline and supporting frame lesson presentation interactive technologies accelerator teaching methods Practice tests, testing online tasks and exercises homework workshops and trainings questions for class discussions Illustrations video and audio materials photographs, pictures, graphs, tables, diagrams, comics, parables, sayings, crosswords, anecdotes, jokes, quotes Add-ons abstracts cheat sheets tips for the curious articles (MAN) literature basic and additional dictionary of terms Improving textbooks and lessons correcting errors in the textbook, replacing outdated knowledge with new ones Only for teachers calendar plans training programs methodological recommendations

I. New material

From the course of natural history and physics you know that various changes occur with bodies and substances.

Before you start studying the topic of the lesson, I suggest you complete the following task, take your time with answers, complete the task to the end.

Exercise:

Look carefully at the pictures and try to answer the following questions:

1. Where can you observe the phenomena presented in the drawings and pictures?

№1	№2	№3
№4	№5	№6

2. Give each phenomenon a name. What substances are involved in the phenomena presented? What happens to each substance in the occurring phenomenon? Write down in your workbooks and fill out the following table:

No. Name of the phenomenon	Substance involved in the phenomenon	Changes occurring in the substance
№1,..
…
№6,..

3. In what phenomena are new substances formed?

4. How and by what criteria 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.Copper wire length changes in summer and winter: increases with heating and decreases with cooling.

3.Volume air in the balloon increases in a warm room.

Changes in substances occurred, but water remained water, copper remained copper, air remained air.

New substances, despite their changes, were not formed.

LET'S ANALYZE THE EXPERIENCE

1. Close the test tube with a stopper with a tube inserted into it

2. Place the end of the tube in a glass of water. We heat the test tube with our hands. The volume of air in it increases, and some of the air from the test tube escapes into a glass of water (air bubbles are released).

3. As the test tube cools, the volume of air decreases and water enters the test tube.

Conclusion. Changes in air volume are a physical phenomenon.

Chemical phenomenon (reaction) – a phenomenon in which new substances are formed.

What signs can be used to determine what happened?chemical reaction ? Some chemical reactions cause precipitation. 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 examples of such reactions in the table.

Signs of chemical reactions
Change in color of the original substance	Change in taste of the original substance	Precipitation	Gas release	Odor appears

REACTION	SIGN
	COLOR CHANGE
	CHANGES IN TASTE
	GAS EVALUATION

Various chemical reactions constantly occur in living and inanimate nature. Our body is also a real factory of chemical transformations of one substance into another.

Let's observe some chemical reactions.

You cannot conduct experiments with fire yourself!!!

Experience 1

Let's hold a piece of white bread containing organic matter over the fire.

We observe:

1. Charring, that is, a change in color;

2. Odor appears.

Conclusion . A chemical phenomenon has occurred (a new substance has been formed - coal)

Experience 2

Let's cook a glass of starch. Add a little water and mix. Then let's drop iodine solution.

We observe:

1. Sign of reaction: color change (blue discoloration of starch)

Conclusion. A chemical reaction has occurred. The starch has turned into another substance.

Experience 3

1. Dissolve a small amount of baking soda in a glass.

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

We are watching:
1. Release of gas bubbles.

Conclusion. The release of gas is one of the signs of a chemical reaction.

Some chemical reactions are accompanied by the release of heat.

Let's sum it up

1. Substances can participate in physical and chemical phenomena

2. Comparative characteristics of physical and chemical phenomena are presented by the following interactive animation

3. Difference between physical and chemical phenomena

·During physical phenomena, the molecules of a substance are not destroyed, the substance is preserved.

· During chemical phenomena, molecules of a substance break down into atoms, and molecules of a new substance are formed from atoms.

Signschemicalreactions

Color change
Precipitation or dissolution