Physical and chemical phenomena

Conducting experiments and observations, we are convinced that substances may change.

Changes of substances that do not lead to the formation of new substances (with other properties), called physical phenomena.

1. Water When heated can proceed to steam, and when cooling - in ice .

2.Copper wire length varies in summer and winter: increases when heated and decreases during cooling.

3.Volume air in the ball increases in the warm room.

Changes with substances occurred, but the water remained water, copper - copper, air - air.

New substances, despite their changes, was not formed.

Experience

1. Close the tube tube with the tube inserted into it

2. Lower the end of the tube into a glass with water. Hand mines a test tube. The amount of air in it increases, and part of the air from the tube goes into a glass with water (air bubbles are distinguished).

3. When cooling the tube, the air volume decreases, and water enters the test tube.

Output. Changes in air volume - physical phenomenon.

Tasks

Bring 1-2 Examples of changes to the substances that can be called physical phenomenon. Write examples in the notebook.

Chemical phenomenon (reaction) - phenomenon new substances are formed.

And for what signs you can determine what happened chemical reaction ? With some chemical reactions, precipitate occurs. Other signs are the change in the color of the starting material, the change in its taste, the separation of gas, isolation, or absorption of heat and light.

Examples of such reactions look at the table

Signs of chemical reactions
Changing the color of the starting matter	Changes in the taste of the source	Loss of precipitate	Gas release	Appearance odor

Reaction	Sign
	Color change
	Change taste
	Gas release

Live I. inanimate nature Everyone is constantly proceeding chemical reactions. Our organism with you is also a real factory of chemical transformations of one substances to others.

We observe for some chemical reactions.

Experiments with fire can not be carried out !!!

Experience 1.

Hand over fire slice white breadcontaining organic matter.

We observe:

1. charring, i.e. color change;

2. the appearance of the smell.

Output . Chemical phenomenon occurred (a new substance was formed - coal)

Experience 2.

Cooking with starch. Add some water, mix. Then the iodine hopper.

We observe a sign of the reaction: Color Change (Starch Image)

Output. Chemical reaction occurred. Starch turned into another substance.

Experience 3.

1. Investigate in a glass not a large number of Drinking soda.

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

We observe the release of gas bubbles.

Output. Gas release is one of the signs of a chemical reaction.

Some chemical reactions are accompanied by heat release.

Tasks

Place a few pieces of raw potatoes in a glass jar (or glass). Add a hydrogen peroxide to them from a home aid kit. Explain, which feature you can determine what a chemical reaction occurred.

I pass, you have noticed something like something like the mother's silver ring with time darkens. Or how rusting a nail. Or how to burn wooden lamps to ash. Well, if my mother does not like silver, and in hiking you did not never go, how tea bag is brewed in the cup you saw sure.

What is common to all these examples? And the fact that they all relate to chemical phenomena.

The chemical phenomenon occurs when some substances turn into others: new substances have another composition and new properties. If you also remember physics, then remember that chemical phenomena occur on a molecular and atomic level, but do not affect the composition of the atomic nuclei.

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

• during the reaction, the precipitate may fall;
• the color of the substance may change;
• the consequence of the reaction flow may be the release of gas;
• it can be isolated either the heat absorbed;
• also, the reaction may be accompanied by the release of light.

Also, a list of conditions necessary for the flow of a chemical response is also defined:

• contact: To react, substances should come into contact.
• grinding: For the successful reaction flow, the substances entering it should be as small as possible are crushed, perfect option - dissolved;
• temperature: Very many reactions directly depend on the temperature of substances (most often they need to be heated, but some on the contrary - cool to a certain temperature).

By writing the chemical reaction equation with letters and numbers, you still describe the essence of the chemical phenomenon. And the law of preserving the mass is the same and most important rules in compiling such descriptions.

Chemical phenomena in nature

Of course, you understand that chemistry is happening not only in test tubes in the school laboratory. You can watch the most impressive chemical phenomena in nature. And their meaning is so great that there would be no life on Earth, if not some of the natural chemical phenomena.

So, the first thing we will talk about photosynthesis. This is a process during which plants absorb carbon dioxide from the atmosphere and under the influence sunlight Oxygen produce. We breathe this oxygen.

In general, photosynthesis flows into two phases, and the lighting is only necessary for one. Scientists conducted various experiments and found out that photosynthesis occurs even when weak lighting. But with an increase in the amount of light, the process is significantly accelerated. It was also observed that if simultaneously increasing the illumination of the plant and raise the temperature, the speed of photosynthesis increases even more. It happens to a certain limit, upon achieving a further increase in illumination ceases to accelerate photosynthesis.

In the process of photosynthesis, photons are involved, which radiates the sun, and special pigment plants molecules - chlorophyll. In plants cells, it is contained in chloroplasts, which is precisely thanks to which the leaves are green.

From the point of view of chemistry, at photosynthesis, there is a chain of transformations, the result of which is oxygen, water and carbohydrates as an energy reserve.

It was originally believed that oxygen is formed as a result of carbon dioxide splitting. However, later Cornelius Van Neil found out that oxygen is formed as a result of water photo polyesis. Late studies confirmed this hypothesis.

You can describe the essence of photosynthesis using this equation here: 6 oxo 2 + 12N 2 O + Light \u003d C 6 H 12 O 6 + 6O 2 + 6N 2 O.

Breathours with you in including, – This 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 breathing. The main thing in this process is that a large amount of energy is distinguished due to breathing, and this method of obtaining it is very effective.

In addition, intermediate outcome different stages Breath is big number various connections. And those in turn serve as the basis for the synthesis of amino acids, proteins, vitamins, fats and fatty acids.

The process of breathing is complex and divided into several stages. At each of which there is a large number of enzymes that perform the role of catalysts. The scheme of chemical respiration reactions is almost the same in animals, plants and even bacteria.

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

By the way, we talked above that chemical reactions may be accompanied by light emission. In the case of breathing and accompanying chemical reactions, this is also true. Some microorganisms can be lit (luminescent). Although the energy efficiency of breathing decreases.

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

They burn, of course, not only solids, just with their help it was more convenient to give an example in this case.

From a chemical point of view, burning is an oxidative reaction that proceeds with very high speed. And with a very, very high reaction speed, an explosion may occur.

Schematically, the reaction can be written as follows: Substance + O 2 → Oxides + Energy.

As a natural chemical phenomenon we consider and ring.

In essence, this is the same process as burning, it only flows much slower. Renigation 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 emergence of rotting.

As a result of chemical reactions from the protein, ammonia, fatty volatile acids, carbon dioxide, oxy acids, alcohols, amines, scatles, indole, hydrogen sulfide, mercaptane are formed. Some of the nitrogen-containing poisonous compounds formed from the rotation of nitrogen-containing compounds.

If we turn back to our list of signs of a chemical reaction, then many of them are detected and in this case. In particular, there is a source substance, reagent, reaction products. Of characteristic signs We note the release of heat, gases (tightness), color change.

For the cycle of substances in nature, rotting is very great importance: Allows you to process proteins of dead organisms in compounds suitable for assimilation by plants. And the circle starts first.

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

Ozone (about 3) in pure form is gas of blue color. In nature, the greatest concentration of ozone - in upper layers Atmosphere. There he fulfills the role of the shield of our planet. Who protects it from solar radiation From space and does not give the earth to cool, because it absorbs and its infrared radiation.

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

In a thunderstorm, under the influence of lightning, part of oxygen molecules disintegrates atoms, molecular and atomic oxygen are connected, and 3 is formed.

That is why we feel special freshness after the thunderstorm, it makes it easier for us, the air seems more transparent. The fact is that ozone is much more strong oxidizerThan oxygen. And in a small concentration (as after a thunderstorm) is safe. And even useful because it decomposes harmful substances in the air. In essence, disinfects it.

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

By the way, the disinfectants of the properties obtained by the laboratory by ozone are widely used for ozonation of water, prevention of products from damage, in medicine and cosmetology.

Of course, this is not full list Amazing chemical phenomena in nature, which make life on the planet so diverse and beautiful. You will be able to learn more about them if you can carefully look around and keep your ears open. Around full amazing phenomena, which are just waiting for you to be interested in.

Chemical phenomena in everyday life

These include those that can be observed in everyday life modern man. Some of them are completely simple and obvious, anyone can observe them in their kitchen: for example, the brewing of tea. Heated boiling water Chanki change their properties, the composition of the water is also changing: it acquires another color, taste and properties. That is, a new substance is obtained.

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

Using the example of a strong (concentrated) tea welding, you can conduct one more experience independently: brighten the tea with the help of the lemon. Due to the acids contained in lemon juice, Liquid will change its composition again.

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

If you simplify, the fuel combustion reaction in the engine can be described as follows: oxygen + fuel \u003d water + carbon dioxide.

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

The combustion of the mixture occurs in the fraction of a second, as a result, the relationship between atoms of hydrogen and carbon is destroyed. Due to this, a large amount of energy is released, which leads to the movement of the piston, and the one is the crankshaft.

In the future, hydrogen and carbon atoms are connected to oxygen atoms, water and carbon dioxide is formed.

Ideally, the fuel combustion reaction 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 so effective. Suppose if the oxygen is not enough when the reaction is slightly, as a result of the reaction, CO is formed. And with a greater lack of oxygen, soot is formed (C).

Formation of plaque on metals As a result of oxidation (rust on iron, patina on copper, silver darkening) - also from the category of household chemical phenomena.

Take iron for example. Rust (oxidation) occurs under the influence of moisture (humidity, direct contact with water). The result of this process becomes iron hydroxide Fe 2 O 3 (more precisely, FE 2 O 3 * H 2 O). You can see it in the form of loose, rough, orange or red brown Nalea on the surface of metal products.

Another example can serve as a green plaque (patina) on the surface of copper and bronze products. 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 carbonate copper is found in nature - in the form of Malachite mineral.

And one more example of a slow oxidative metal reaction in living conditions - This is the formation of a dark salt of silver sulfide AG 2 S on the surface of silver products: jewelry, cutlery, etc.

"Responsibility" for its occurrence carry sulfur particles, which in the form of hydrogen sulfide are present in the air, which we breathe with you. Darmeted silver can and when contact with sulfur-containing food products (eggs, for example). The reaction looks like this: 4Ag + 2H 2 S + O 2 \u003d 2AG 2 S + 2H 2 O.

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

In living conditions there is no chemically clean water, it is always dissolved in various concentrations of metals and other substances. If water is saturated with calcium and magnesium salts (hydrocarbonates), it is called tough. The higher the concentration of salts, the more rigid is water.

When such water is heated, these salts are exposed to carbon dioxide and insoluble precipitate (Saco 3 andMG.CO 3). These solid deposits you can watch by looking at the kettle (as well as looking at heating elements washing and dishwashers, irons).

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

By the way, having gathered to get rid of scale in the kettle, you can observe another example entertaining chemistry In everyday life: the usual table vinegar and deposits are well coped and lemon acid. A teapot with a solution of vinegar / citric acid and water is boiled, after which the scale disappears.

And without a different chemical phenomenon there would be no delicious mother cakes and buns: it's about gassing soda vinegar.

When mom quit soda in a spoon of vinegar, this reaction occurs: NaHCO 3 + CH. 3 COOH \u003d.Ch 3 Coona. + H. 2 O. + Co. 2 . The carbon dioxide resulting in its result is striving to leave the dough - and thereby changes its structure, makes porous and loose.

By the way, you can tell my mother that it is not necessary to quench the soda - she will react when the dough gets into the oven. The reaction, however, will take place a little worse than with soda quenching. But at a temperature of 60 degrees (and better than 200), soda decomposition on sodium carbonate, water and all the same carbon dioxide. True, the taste of ready-made pies and buns can be worse.

The list of household chemical phenomena is no less impressive than a list of such phenomena in nature. Thanks to them, we have roads (the manufacture of asphalt is a chemical phenomenon), at home (brick firing), beautiful cloths for clothing (staining). If you think about it, it becomes clearly clear how many-sided and interesting science chemistry. And how much benefit can be learned from understanding its laws.

Among many and many people invented by nature and the man's phenomena are special, which is difficult to describe and explain. These applies and water burning. As such, maybe you ask, because water is not lit, the fire extinguishes it? How can she burn? And the thing is what.

Water burning is a chemical phenomenonIn which in water with an admixture of salts under the influence of radio waves, oxygen-hydrogen bonds tear. As a result, oxygen and hydrogen is formed. And burning, of course, not the water itself, but by hydrogen.

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

This phenomenon has long been interested in scientists who dream learn how to use water as fuel. For example, for cars. While it is something from the field of fiction, but who knows that scientists will be able to invent very soon. One of the main catch is that with the burning of water of energy, more than the reaction is spent.

By the way, something similar can be observed in nature. According to one of theories, large lone waves that seem to be from nowhere are actually a consequence of a hydrogen explosion. Electrolysis of water, which leads to it, is carried out by entering electrical discharges (lightning) to the surface of the salt water of the seas and oceans.

But not only in water, but on land you can observe the imaginable chemical phenomena. If you had a chance to visit the natural cave, you probably could see the bizarre, beautiful natural "icicles" hanging from the ceiling - stalactites. The way and why they appear, is explained by another interesting chemical phenomenon.

Chemist, looking at Stalatitis, sees, of course, not an icicle, but Calcium carbonate SASI 3. The basis for his education is served wastewater, natural limestone, and the stalactite itself is built due to the precipitation of calcium carbonate (rising down) and the force of the clutch of atoms in crystal lattice (Growth of Washier).

By the way, similar formations can rise from the floor to the ceiling - they are called stalagmitians. And if stalactites and stalagmites meet and grow into solid columns, they get a name staples.

Conclusion

There are many amazing, beautiful, as well as dangerous and frightening chemical phenomena daily in the world. Of many people learned to benefit: Creates construction MaterialsPreparing food, makes transport move to huge distances and much more.

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

Fermentation allows you to prepare food, and the chemical phenomenon with it is decomposing proteins on more simple compounds And returns those in the cycle of substances in nature.

The formation of oxide when heating copper, accompanied by a bright glow, combustion of magnesium, melting sugar, etc. also consider chemical phenomena. And they find useful use.

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1. Tight contact of the reactant substances (necessary): H 2 SO 4 + Zn \u003d ZnSO 4 + H 2 2. Heating (possibly) a) to start the reaction b) constantly Classification of chemical reactions by various signs 1. On the presence of the border of the phase partition, all chemical reactions are divided into homogenic and heterogeneous Chemical reaction occurring within the same phase is called homogeneous chemical reaction. Chemical reaction occurring on the border of the phase section is called heterogeneous chemical reaction. In a multistage chemical reaction, some stages may be homogeneous, while others are heterogeneous. Such reactions are called homogeneous heterogeneous . Depending the number of phases, which form the starting materials and reaction products, the chemical processes can be homofaznic (starting materials and products are within the same phase) and heterophase (source substances and products form several phases). The homo- and heterophasity of the reaction is not related to whether the reaction is homo- or heterogeneous. Therefore, you can select four types of processes: Homogeneous reactions (homofamine). In the reactions of this type, the reaction mixture is homogeneous, and reagents and products belong to the same phase. An example of such reactions can be the reactions of ion exchange, for example, neutralization of the acid solution with a solution of a rhytholic: Heterogeneous homofamine reactions. Components are within the same phase, but the reaction proceeds on the border of the phase partition, for example, on the surface of the catalyst. An example may be hydrogenation of ethylene on a nickel catalyst: Homogeneous heterophase reactions. Reagents and products in such a reaction exist within several phases, but the reaction proceeds in one phase. This can pass the oxidation of hydrocarbons in the liquid phase with gaseous oxygen. Heterogeneous heterophase reactions. In this case, the reagents are in different phase state, the reaction products can also be in any phase state. The reaction process takes place on the border of the phase partition. An example is the reaction of carbonic acid salts (carbonates) with Brenstened acids: 2. By changing the degrees of the oxidation of the reagents [edit | Edit Wiki-text] In this case, the redox reactions in which the atoms of one element (oxidant) are distinguished restore that is, lower its degree of oxidation, and the atoms of another element (reducing agent) oxidize that is, increase their degree of oxidation. A special case of oxidative reaction reactions are the Reactions of Corporation, in which the oxidizing agent and the reducing agent are atoms of the same element in different degrees of oxidation. An example of a redox reaction is the combustion of hydrogen (reducing agent) in oxygen (oxidizing agent) to form a water: an example of a consolidation reaction is the reaction of the decomposition of ammonium nitrate when heated. The oxidizer in this case protrudes the nitrogen (+5) nitro groups, and the reducing agent - nitrogen (-3) of ammonium cation: do not relate to the redox reaction, in which there is no change in the degrees of atomic oxidation, for example: 3. by the thermal effect of the reaction, all chemical Reactions are accompanied by excretion or energy absorption. When breaking chemical ties In the reagents, the energy is distinguished, which is mainly on the formation of new chemical bonds. In some energy reactions of these processes are close, and in this case, the total thermal effect of the reaction is approaching zero. In other cases, it is possible to distinguish: exothermic reactions that go with heat release, (positive thermal effect) CH 4 + 2O 2 \u003d CO 2 + 2N 2 O + Energy (light, heat); Sao + H 2 O \u003d CA (OH) 2 + Energy (Heat). Endothermic reactions during which heat is absorbed (negative thermal effect) from the environment. SA (OH) 2 + Energy (Heat) \u003d Sao + H 2 About the thermal effect of the reaction (reaction enthalpy, Δ r H), often having very important, can be calculated according to the GESS law, if the enthalpy of formation of reagents and products is known. When the sum of the enthalpium products is less than the sum of the enthalpy of the reagents (Δ R H< 0) наблюдается выделение тепла, в противном случае (Δ r H > 0) - absorption. 4. In the type of transformation of reacting particles [edit | Edit Wiki-text] Connections: decomposition: substitution: exchange (including reaction type-neutralization): Chemical reactions are always accompanied by physical effects: the absorption or excretion of energy, the change in the color of the reaction mixture, etc. it is precisely for these physical effects. about the flow of chemical reactions. Connection reactionA chemical reaction, as a result of which only one new one is formed from two or more of the starting materials. In such reactions can enter both simple and complex substances. Reaction decompositionA chemical reaction, as a result of which several new substances are formed from a single substance. In the reaction this type Only complex compounds come, and their products can be both complex and simple substances. Recovery reactionThe chemical reaction, as a result of which the atoms of one element included in the composition 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 should be simple, and the other is complex. Exchange reactions- reaction, as a result of which two complex substances exchange their component parts 5. As a sign of the flow direction, chemical reactions are divided into irreversible and reversible Irreversible Call chemical reactions occurring only in one direction (" from left to right"), As a result, the initial substances are converted into reaction products. About such chemical processes They say that they proceed "to the end". reactions burning, as well as reactions accompanied by the formation of poorly soluble or gaseous substances Reversible The chemical reactions occur simultaneously in two opposite directions ("from left to right" and "right to left"). In equations of such reactions, the equal sign is replaced by two opposite arrows. In two simultaneously flowing reactions distinguish straight (leaks "left right") and inverse(Spent "right to left"). Since during a reversible reaction, the starting materials are simultaneously and are consumed and formed, they are not fully converted into reaction products. Therefore, we say about reversible reactions that they proceed "not to the end". As a result, a mixture of starting materials and interaction products is always formed. 6. In the sign of the participation of catalysts, chemical reactions are divided into catalytic and noncatalithic Catalytic 2SO 2 + O 2 → 2SO 3 (catalyst V 2 O 5) is called reactions flowing in the presence of catalysts. In the equations of such reactions chemical formula The catalyst indicates the sign of equality or reversibility, sometimes together with the designation of the conditions of the flow. The reactions of this type include many decomposition reactions and compounds. Necatalytic2no + O2 \u003d 2NO 2 is called many reactions flowing into the absence of catalysts. This, for example, the reaction of exchanging and substitution.

I. New material

From the course of nature and physics, you know that a variety of changes are taking place with bodies and substances.

Before starting studying the lesson, I suggest you to perform the following task, do not hurry with the answers, perform the task to the end.

The task:

Consider carefully pictures and try to answer the following questions:

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

№1	№2	№3
№4	№5	№6

2. Give the name to each phenomenon. What substances are involved in the submitted phenomena? What happens to every substance in what is happening? Write down in the working notebooks and fill out the following table:

№, phenomenon name	Phenomenon	Changes occurring with a substance
№1,..
…
№6,..

3. In which phenomena new substances are formed?

4. How and for what features you can divide the submitted phenomena?

Physical and chemical phenomena

Conducting experiments and observations, we are convinced that substances may change.

Changes of substances that do not lead to the formation of new substances (with other properties), called physical phenomena.

1. Water When heated can proceed to steam, and when cooling - in ice .

2. Length copper wires varies in summer and winter: increases when heated and decreases during cooling.

3. Volume Air in the ball increases in the warm room.

Changes with substances occurred, but the water remained water, copper - copper, air - air.

New substances, despite their changes, was not formed.

Let's analyze the experience

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

2. Lower the end of the tube into a glass with water. Hand mines a test tube. The amount of air in it increases, and part of the air from the tube goes into a glass with water (air bubbles are distinguished).

3. When cooling the test tube, air volume decreases, and water enters the tube.

Output. Changes in air volume - physical phenomenon.

Chemical phenomenon (reaction) - phenomenon new substances are formed.

And for what signs you can determine what happenedchemical reaction ? With some chemical reactions, precipitate occurs. Other signs are the change in the color of the starting material, the change in its taste, the separation of gas, isolation, or absorption of heat and light.

Examples of such reactions look at the table

Signs of chemical reactions
Changing the color of the starting matter	Changes in the taste of the source	Loss of precipitate	Gas release	Appearance odor

REACTION	Sign
	COLOR CHANGE
	Change taste
	Gas release

In a living and inanimate nature, various chemical reactions constantly proceed. Our organism with you is also a real factory of chemical transformations of one substances to others.

We observe for some chemical reactions.

Experiments with fire can not be carried out !!!

Experience 1.

We carry out a piece of white bread containing organic substances over the fire.

We observe:

1. charring, i.e. color change;

2. The appearance of the smell.

Output . Chemical phenomenon occurred (a new substance was formed - coal)

Experience 2.

Prepare glass with starch. Add some water, mix. Then Capiodine solution.

We observe:

1. Sign of reaction: Color Change (Starch Image)

Output. Chemical reaction occurred. Starch turned into another substance.

Experience 3.

1. Investigate a small amount of drinking soda in a glass.

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

We observe:
1. Isolation of gas bubbles.

Output. Gas release is one of the signs of a chemical reaction.

Some chemical reactions are accompanied by heat release.

Let's summarize

1. Substances can participate in physical and chemical phenomena

2. The comparative characteristic of physical and chemical phenomena is presented by the following interactive animation.

3. The difference of physical and chemical phenomena

· In physical phenomena, the substance molecules are not destroyed, the substance is preserved.

· In case of chemical phenomena of the substance molecule decompose on atoms, the molecules of a new substance are formed from atoms.

Signschemicalreactions

Color change
Loss or dissipation