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 signs 1. Based on 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 substances and reaction products, chemical processes can be homophasic (the starting substances and products are within one phase) and heterophasic (the 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] B in this case distinguish 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.By thermal effect reactions 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), often having a 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 less than the amount enthalpies of 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. In reaction of this type only complex compounds enter, and their products can be both complex and simple substances Substitution reaction-chemical reaction as a result which atoms of one element that make up 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 they say that they do not proceed “to the end”. 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.

Depending on the ratio of graphite and clay, a lead of varying softness is obtained; the more graphite, the softer the lead. The composition of colored pencil leads includes kaolin, talc, stearin (known to a wide range of people as a material for making candles) and calcium stearate (calcium soap).

Matches Matches are manufactured in accordance with GOST. To avoid smoldering, match straws are impregnated with a 1.5% solution phosphoric acid, and then paraffinized (dipped in molten paraffin). GOST

Glass Glass is a material with an amorphous-crystallite structure, obtained by supercooling the melt. With a gradual increase in viscosity, glass acquires mechanical properties solids. The process of transition from a liquid to a glassy state is reversible: with increasing temperature, the glass gradually softens, turning first into a viscous and then into a liquid state; this process underlies the molding of products.

Some other oxides are aluminum, magnesium, used to improve the physical properties of glass, including resistance to atmospheric pollution. Other metal oxides may be included in body-dyed glass. Composition: quartz - raw material, in the form of sand (70-72%); soda, reaction catalyst, carbonate and sulfate (about 14%); lime, stabilizer, in solid form (about 10%);

Composition: One of the variants of the chemical composition of solid soap C 17 H 35 COONa (liquid C 17 H 35 COOK). Modern liquid soaps are aqueous solutions synthetic ionic or non-ionic surfactants with the addition of preservatives, fragrances, dyes, salts to control viscosity, additives to bind calcium and magnesium ions, etc. When cooling the adhesive soap, it turns out laundry soap. Solid soap contains% of the main substance, 0.1-0.2% of free alkali, 1-2% of free Na or K carbonates, 0.5-1.5% of water-insoluble residue.

The French chemist Chevreul discovered stearic, palmitic and oleic acids as products of the decomposition of fats when they are saponified with water and alkalis. In the production of soap, rosin has long been used, which is obtained by processing the resin of coniferous trees. Introduction of rosin into large quantities makes soap soft and sticky. In addition to using soap as detergent it is widely used in finishing fabrics, in production cosmetics, for the production of polishing compounds and water-based paints.

It is best if the storage location for this kind of funds is located outside the actual residential premises. Such a place could be, for example, a glazed loggia. Required condition– place medications household chemicals out of reach of children's hands.

In addition, keep in mind that all these “helpful helpers”, all these chemicals in everyday life, despite some, of course, undeniable advantages, are dangerous in that any of them may turn out to be an allergen for you or your loved ones. This circumstance is perhaps the most important and predetermines the need for their careful use.

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 – color change starting material, changing its taste, releasing gas, releasing or absorbing 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 occurring. Our body too real factory chemical transformations some substances into others.

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 there (you can take lemon juice or a solution of 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 in a glass jar (or glass) raw potatoes. Add hydrogen peroxide from home first aid kit. Explain how you can determine that a chemical reaction has occurred.

Physical changes are not associated with chemical reactions and the creation of new products, such as melting ice. As a rule, such transformations are reversible. In addition to examples physical phenomena, in nature and in everyday life There are also chemical transformations in which new products are formed. Such chemical phenomena (examples will be discussed in the article) are irreversible.

Chemical changes

Chemical changes can be thought of as any phenomenon that allows scientists to measure chemical properties. Many reactions are also examples of chemical phenomena. While it's not always easy to tell that a chemical change has occurred, there are some telltale signs. What are chemical phenomena? Let's give examples. This may be a change in the color of the substance, temperature, the formation of bubbles or (in liquids) the formation of a precipitate. You can cite following examples chemical phenomena in life:

1. Rust on iron.
2. Burning wood.
3. Metabolism of food in the body.
4. Mixing acid and alkali.
5. Cooking the egg.
6. Digestion of sugar by amylase in saliva.
7. Mixing baking soda and vinegar to create carbon dioxide gas.
8. Baking a pie.
9. Metal galvanization.
10. Batteries.
11. Fireworks explosion.
12. Rotting bananas.
13. Formation of lactic acid products.

And this is not the entire list. We can look at some of these points in more detail.

Outdoor fire using wood

Fire - this is also an example of a chemical phenomenon. This is the rapid oxidation of a material in an exothermic chemical process combustion, releasing heat, light and various reaction products. The fire is hot because there is a conversion of the weak double bond in molecular oxygen O2 to stronger bonds in the products of combustion carbon dioxide and water. Great energy is released (418 kJ per 32 g O 2); The binding energies of the fuel play only a minor role here. IN certain moment a combustion reaction called the flash point produces a flame.

This visible part fire, which consists mainly of carbon dioxide, water vapor, oxygen and nitrogen. If the temperature is high enough, the gases can become ionized to produce plasma. Depending on what substances are ignited and what impurities are supplied from outside, the color of the flame and the intensity of the fire will be different. Fire in its most common form can result in a fire that can cause physical damage when burned. Fire is important process, which affects ecological systems around the world. Positive effects fires include stimulating the growth and maintenance of various ecological systems.

Rust

Just like fire, the rusting process is also an oxidative process. Just not as fast-moving. Rust is an iron oxide, usually a red oxide, formed by the redox reaction of iron and oxygen in the presence of water or air. Several forms of rust are distinguished both visually and spectroscopically and form under different circumstances. Given enough time, oxygen and water, any mass of iron will eventually completely turn to rust and decompose. The surface portion is flaky and crumbly, and does not protect the underlying iron, unlike the patina that forms on copper surfaces.

An example of a chemical phenomenon, rusting is a general term for the corrosion of iron and its alloys such as steel. Many other metals undergo similar corrosion, but the resulting oxides are not usually called rust. Other forms of this reaction exist as a result of the reaction between iron and chloride in an oxygen-deprived environment. An example is the rebar used in underwater concrete pillars, which generates green rust.

Crystallization

Another example of a chemical phenomenon is crystal growth. This is a process in which a pre-existing crystal becomes larger as the number of molecules or ions in their positions in crystal lattice. A crystal is defined as atoms, molecules or ions arranged in an ordered repeating pattern, a crystal lattice, extending in all three spatial dimensions. Thus, crystal growth differs from the growth of a liquid drop in that during growth molecules or ions must enter correct positions lattice so that an ordered crystal can grow.

When molecules or ions fall into positions different from those in an ideal crystal lattice, crystal defects are formed. Typically, molecules or ions in a crystal lattice are trapped in the sense that they cannot move from their positions, and therefore crystal growth is often irreversible, since once the molecules or ions have fallen into place in the growing lattice, they are fixed in it. Crystallization is a common process in both industry and the natural world, and crystallization is generally understood to consist of two processes. If there was no previously existing crystal, then a new crystal must be born, and then it must undergo growth.

Chemical origin of life

The chemical origin of life refers to the conditions that might have existed and therefore contributed to the emergence of the first duplicated life forms.

The main example of chemical phenomena in nature is life itself. It is believed that a combination of physical and chemical reactions could lead to the appearance of the first molecules, which, by reproducing, led to the emergence of life on the planet.

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. The water in a glass or other container will turn red-brown. A chemical reaction will occur: 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 properties peculiar only to it. quality characteristics. 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 “identifying signs”:

• 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 for the occurrence of 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 regular form. 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 occur through physical formulas, solving physical problems.