Solidification of bodies. Solidification of crystalline bodies. Melting of amorphous bodies

Many novice builders are familiar with the inevitable appearance of defects on the surface of concrete: small cracks, chips, rapid failure of the coating. The reason is not only non-compliance with concreting rules, or the creation of a cement mortar with an incorrect ratio of components; more often, the problem lies in the lack of care for the concrete during the hardening stage.

The setting time of the cement mortar depends on numerous factors: temperature, humidity, wind, exposure to direct sunlight, etc. It is important to moisten the concrete during the hardening stage, this will ensure maximum strength and integrity of the coating.

The setting time of cement mortar depends on numerous factors

General information

Depending on the temperature at which the cement hardens, the hardening period also differs. The best temperature is 20°C. Under ideal conditions, the process takes 28 days. In hot regions or during cold periods of the year, it is difficult or impossible to maintain this temperature.

In winter, concreting is required for a number of reasons:

• laying the foundation for a building located on crumbling soils. During the warm period of the year it is impossible to carry out construction;
• In winter, manufacturers make discounts on cement. Sometimes you can really save a lot on material, but storing it until it gets warmer is an undesirable solution, because the quality of the cement will decrease. Pouring concrete on the interior surfaces of buildings and even exterior work in winter is quite appropriate if discounts are available;
• private concreting work;
• In winter there is more free time and it is easier to take a vacation.

The disadvantage of working in cold weather is the difficulty of digging a trench and the need to equip a heating area for workers. Taking into account additional costs, savings do not always occur.

Features of pouring concrete at low temperatures

The hardening time of the cement mortar depends on the temperature. At low temperatures, the time increases significantly. In the construction industry, it is customary to call the weather cold when the thermometer drops to an average of 4°C. To successfully use cement in cold weather, it is important to take protective measures to prevent the mortar from freezing.

The setting of concrete at low temperatures proceeds somewhat differently; the water temperature has the greatest impact on the final result. The warmer the liquid, the faster the process proceeds. Ideally, for winter it is worth ensuring the thermometer reading is at 7-15°. Even in conditions of heated water, the surrounding cold slows down the rate of hydration of the cement mortar. It takes longer to gain strength and set.

To calculate how long cement hardens, it is important to take into account the fact that a drop in temperature by 10° leads to a 2-fold reduction in the hardening rate. It is important to carry out calculations, since premature removal of formwork or use of concrete can lead to destruction of the material. If the ambient temperature drops to -4°C and there are no additives, insulation or heating, the solution will crystallize and the cement hydration process will stop. The final product will lose 50% of its strength. The hardening time will increase by 6-8 times.

Despite the fact that you should determine how long the concrete hardens, and you have to control the hardening process, there is a downside - the opportunity to improve the quality of the result. Reducing the temperature increases the strength of concrete, but only to the critical level of -4°C, although the procedure takes more time.

Factors affecting hardening

At the planning stage of work with cement, an important factor influencing the final result is the rate of concrete dewatering. The hydration process is influenced by numerous factors; it is possible to more accurately determine how much the cement mortar hardens by taking into account the following factors:

• environment. Humidity and air temperature are taken into account. In high dryness and heat, concrete will harden in just 2-3 days, but it will not have time to acquire the expected strength. Otherwise, it will remain wet for 40 days or more;

• filling density. As the cement compacts, the rate of moisture release decreases, this improves the hydration procedure, but slightly reduces the speed. It is better to compact the material using a vibrating plate, but manually piercing the solution is also suitable. If the composition is dense, it will be difficult to process after hardening. At the stage of finishing or laying communications in compacted concrete, it is necessary to use diamond drilling, since pobedit drills quickly wear out;
• composition of the solution. The factor is quite important, because the level of porosity of the filler affects the rate of dehydration. The solution with expanded clay and slag hardens more slowly, moisture accumulates in the filler, and it is released slowly. With gravel or sand, the composition dries faster;
• presence of additives. Special additives with moisture-retaining properties help to reduce or accelerate the stages of hardening of the solution: soap solution, bentonite, antifreeze additives. The purchase of such components increases the amount of work, but many additives simplify the work with the composition and increase the quality of the result;
• formwork material. The hardening time of cement depends on the tendency of the formwork to absorb or retain moisture. The rate of hardening is affected by porous walls: unsanded boards, plastic with through holes or loose installation. The best way to complete construction work on time and while maintaining the technical characteristics of concrete is to use metal panels or install plastic film on top of board formwork.

The type of base also influences how long the cement mortar hardens. Dry soil quickly absorbs moisture. When concrete hardens in the sun, the hardening time increases significantly; to prevent the material from obtaining low strength, the surface should be constantly moistened and the area shaded.

Artificially increasing the rate of hardening

The hardening time of cement mortar in cold weather increases greatly, but the time frame still remains limited. To speed up the procedure, various techniques have been developed.

In modern construction, drying time can be accelerated by:

• adding additives;
• electric heating;
• increasing the required proportions of cement.

Using Modifiers

The easiest way to complete work on time even in winter is to use modifiers. When a certain proportion is added, the hydration period is reduced; when using some additives, hardening occurs even at -30°C.

Conventionally, additives that affect the rate of hardening are divided into several groups:

• type C – drying accelerators;
• type E – water-substituting additives with accelerated hardening.

The foundation hardening calculator and reviews show maximum effectiveness when potassium chloride is added to the solution. The material is consumed economically, since its mass fraction is up to 2%.

If you use type C concrete curing mixtures, you should take care of heating, since they do not protect against freezing.

It is recommended to take care of laying communications in the foundation or screed in advance, otherwise drilling holes will be required. Making communication holes after hardening will lead to the need for a special tool and. The procedure is quite labor-intensive and reduces the strength of the structure.

Concrete heating

Mostly, a special cable is used to heat the composition, which converts electric current into heat. The technique provides the most natural way of hardening. An important factor is the need to follow the instructions for installing the wire. The method protects against liquid crystallization; there are also tools (hair dryer, welding machine) and thermal insulation to protect against freezing.

Increasing cement dosage

Increasing the cement concentration is used only with a slight decrease in temperature. It is important to increase the dosage in small quantities, otherwise the quality and durability will be significantly reduced.

Concrete is a multifunctional composition from which any structure can be built. In modern construction, a variety of cement compositions and methods of processing are used:

• The first stage of building construction is drawing up a diagram and calculating the load. Strength depends on various characteristics. It is important to follow all masonry rules to obtain design strength;

• common in private construction. They improve thermal insulation properties, reduce the load on the foundation, and make it easy and quick to lay walls. You can make them yourself. are formed using a similar algorithm with blocks;
• in wet areas there is a need for additional protection of concrete. A special one is used, since standard mixtures do not completely cover the concrete wall;
• One of the most popular and frequent procedures for working with mortar is screeding. The proportions of cement and sand for the screed differ depending on the task at hand.

Conclusion

Concreting in hot or cold conditions requires special measures. If ideal conditions for hydration of concrete are created, it will acquire high strength, be able to withstand significant load-bearing loads and become resistant to destruction. The main task of the builder is to prevent freezing or premature drying of the solution.

Knowing the hardening time of concrete, you can plan further construction processes in advance.

There are several factors on which the quality indicators of a newly erected building depend:

• air temperature;
• atmospheric humidity;
• brand of cement;
• compliance with installation technology;
• care of the screed during the drying period.

Polymerization of concrete

This complex multi-step process of strengthening and drying can be adjusted, but to do this you need to understand what it is.

The hardening stage of concrete and other building mixtures based on cement begins with setting. The solution and water in the formwork react, and this gives impetus to the acquisition of structure and strength properties.

Grasping

The time required for setting will directly depend on various influences. For example, the atmospheric temperature is 20 °C, and the foundation is formed using M200 cement. In this case, hardening will begin no earlier than after 2 hours and will last almost as long.

Curing

After the setting phase, the screed begins to harden. At this stage, the main proportion of cement granules and water in the solution begin to interact (a cement hydration reaction occurs). The process takes place most optimally at atmospheric humidity of 75% and air temperature from +15 to +20 °C.

If the temperature has not risen to +10 degrees, there is a very high probability that the concrete will not reach its design strength. That is why, in winter conditions and when working outdoors, the solution is combined with special anti-frost additives.

Strength gain

The structural strength of a floor or any other structure and the time it takes for the cement mortar to harden are directly related. If the water leaves the concrete faster than necessary for setting and the cement does not have time to react, then after a certain period after drying we will encounter loose segments, leading to cracks and deformation of the screed.

These defects can be observed when cutting concrete products with a grinder, when the heterogeneous structure of the slab indicates a violation of the technological process.

According to technological rules, the concrete foundation dries for at least 25 - 28 days. However, for structures that do not perform increased load-bearing functions, this period is allowed to be reduced to five days, after which they can be walked on without fear.

Impact factors

Before starting construction work, it is necessary to take into account all factors that could in one way or another influence the drying time of concrete.

Seasonality

Of course, the environment has the main influence on the drying process of cement mortar. Depending on the temperature and atmospheric humidity, the period for setting and complete drying may be limited to a couple of days in the summer (but the strength will be low) or the structure will retain a large amount of water for more than 30 days during cold weather.

The strengthening of concrete under normal temperature conditions can be better explained by a special table that indicates how long it will take to achieve the maximum effect.

Tamping

Much also depends on the density of the construction mixture. Naturally, the higher it is, the slower the moisture leaves the structure and the better the cement hydration indicators will be. In industrial construction, this problem is solved with the help of vibration treatment, but at home they usually get by with bayoneting.

It is worth remembering that a dense screed is more difficult to cut and drill after compaction. In such cases, diamond-coated drills are used. Drills with a regular tip instantly fail.

Compound

The presence of various components in the building mixture also affects the setting process. The more porous materials (expanded clay, slag) in the solution, the slower the dehydration of the structure will occur. In the case of sand or gravel, on the contrary, the liquid will come out of solution faster.

To slow down the evaporation of moisture from concrete (especially in high temperature conditions) and improve its strength, they resort to the use of special additives (concrete, soap composition). This will somewhat affect the cost of the filling mixture, but will prevent premature drying.

Providing drying conditions

To keep moisture in the mortar mixture longer, you can lay waterproofing material on the formwork. If the molding frame is made of plastic, no additional waterproofing is required. Dismantling of the formwork is carried out after 8 - 10 days - this hardening time is enough, then the concrete can dry without formwork.

Supplements

You can also retain moisture in the thickness of the concrete floor by introducing modifiers into the building mixture. In order to be able to walk on the poured surface as quickly as possible, you will have to add special components to the solution for rapid hardening.

Reduced evaporation

Immediately after setting, the concrete surface is covered with polyethylene, which significantly reduces the evaporation of moisture in the first days after installation of the structure. Once every three days, the film is removed and the presence of dust and cracks is checked by pouring water on the floor.

On the twentieth day, the polyethylene is removed and the screed is allowed to dry completely as usual. After 28 - 30 days, you can not only walk on the foundation, but also load it with building structures.

Strength of concrete

Knowing how long it will take for a concrete pour to dry completely, and how to properly organize such an important process, you can avoid mistakes and maintain the strength of the building element. The table contains more detailed information on concrete strength indicators by cement grade.

Lesson topic: “Specific heat of fusion. Melting graphs and

solidification of crystalline bodies."

Lesson objectives:

Develop the ability to plot a graph of the temperature of a crystalline body depending on the heating time;

Introduce the concept of specific heat of fusion;

Enter a formula to calculate the amount of heat required to melt a crystalline body of mass m, taken at the melting temperature.

Develop the ability to compare, contrast, and generalize material.

Accuracy in drawing up schedules, hard work, the ability to complete the work started.

Epigraph to the lesson:

“Without a doubt, all our knowledge begins with experience.”

Kant (German philosopher 1724 - 1804)

“It’s not a shame not to know, it’s a shame not to learn”

(Russian folk proverb)

Lesson progress:

I. Organizational moment. Setting the topic and goals of the lesson.

II. The main part of the lesson.

1. Updating knowledge:

There are 2 people at the board:

Fill in the missing words in the definition.

“The molecules in crystals are located..., they move..., held in certain places by the forces of molecular attraction. When bodies are heated, the average speed of movement of molecules ..., and the vibrations of molecules ..., the forces that hold them, ..., the substance passes from a solid to a liquid state, this process is called ... ".

“The molecules in a molten substance are located..., they move... and... are held in certain places by forces of molecular attraction. When a body cools, the average speed of movement of molecules ..., the range of vibrations ..., and the forces holding them ..., the substance passes from a liquid state to a solid, this process is called ... ".

The rest of the class works on mini-test cards ()

Using table values ​​in the collection of Lukashik problems.

Option #1

1. Lead melts at a temperature of 327 0C. What can you say about the solidification temperature of lead?

A) It is equal to 327 0C.

B) It is higher than the temperature

melting.

2. At what temperature does mercury acquire a crystalline structure?

A) 4200C; B) - 390C;

3. In the ground at a depth of 100 km, the temperature is about 10,000C. Which metal: Zinc, tin or iron is there in an unmolten state.

A) zinc. B) Tin. B) Iron

4. The gas coming out of the nozzle of a jet aircraft has a temperature of 500 - 7000C. Can the nozzle be made from?

A) It’s possible. B) It is impossible.

Melting and solidification of crystalline bodies.

Option No. 2

1. When a crystalline substance melts, its temperature ...

B) decreases.

2. At what temperature can zinc be in a solid and liquid state?

A) 4200C; B) - 390C;

B) 1300 - 15000С; D) 00C; D) 3270C.

3. Which metal: zinc, tin or iron will melt at the melting temperature of copper?

A) zinc. B) Tin. B) Iron

4. The temperature of the outer surface of the rocket during flight rises to 1500 - 20000C. What metals are suitable for making the outer skin of rockets?

A) Steel. B). Osmium. B) Tungsten

D) Silver. D) Copper.

Melting and solidification of crystalline bodies.

Option No. 3

1. Aluminum hardens at a temperature of 6600C. What can you say about the melting point of aluminum?

A) It is equal to 660 0C.

B) It is below the melting point.

B) It is higher than the temperature

melting.

2. At what temperature does the crystalline structure of steel collapse?

A) 4200C; B) - 390C;

B) 1300 - 15000С; D) 00C; D) 3270C.

3. On the surface of the Moon at night the temperature drops to -1700C. Is it possible to measure this temperature with mercury and alcohol thermometers?

A) It’s impossible.

B) You can use an alcohol thermometer.

C) You can use a mercury thermometer.

D) You can use both mercury and alcohol thermometers.

4. Which metal, when in a molten state, can freeze water?

A) Steel. B) zinc. B) Tungsten.

D) Silver. D) Mercury.

Melting and solidification of crystalline bodies.

Option No. 4

1. During crystallization (solidification) of a molten substance, its temperature ...

A) will not change. B) increases.

B) decreases.

2. The lowest air temperature -88.30C was recorded in 1960 in Antarctica at the Vostok scientific station. What thermometer can be used in this place on Earth?

A) Mercury. B) Alcohol

C) You can use both mercury and alcohol thermometers.

D) Neither mercury nor alcohol thermometers should be used.

3. Is it possible to melt copper in an aluminum pan?

A) It’s possible. B) It is impossible.

4. Which metal has a crystal lattice that is destroyed at the highest temperature?

A) In steel. B) In copper. B) In tungsten.

D) Platinum D) Osmium.

2. Checking what is written at the board. Bug fixes.

3. Studying new material.

a) Film demonstration. "Melting and crystallization of a solid"

b) Constructing a graph of changes in the physical state of the body. (2 slide)

c) detailed analysis of the graph with analysis of each segment of the graph; study of all physical processes occurring in a particular interval of the graph. (3 slide)

melting?

A) 50 0С B) 1000С C) 6000С D) 12000С

0 3 6 9 min.

D) 16 min. D) 7 min.

Option No. 2 0C

segment AB? 1000

D) Hardening. B C

segment BV?

A) Heating. B) Cooling. B) Melting. 500

D) Hardening D

3. At what temperature did the process begin?

hardening?

A) 80 0C. B) 350 0С C) 3200С

D) 450 0С D) 1000 0С

4. How long did it take for the body to harden? 0 5 10 min.

A) 8 min. B) 4 min. B) 12 min.

D) 16 min. D) 7 min.

A) Increased. B) Decreased. B) Has not changed.

6. What process on the graph characterizes the VG segment?

A) Heating. B) Cooling. B) Melting. D) Hardening.

Graph of melting and solidification of crystalline solids.

Option No. 3 0C

1.Which process on the graph characterizes 600 G

segment AB?

A) Heating. B) Cooling. B) Melting.

D) Hardening. B C

2. What process on the graph characterizes

segment BV?

A) Heating. B) Cooling. B) Melting. 300

D) Hardening.

3. At what temperature did the process begin?

melting?

A) 80 0С B) 3500С C) 3200С D) 4500С

4. How long did it take for the body to melt? A

A) 8 min. B) 4 min. B) 12 min. 0 6 12 18 min.

D) 16 min. D) 7 min.

5. Did the temperature change during melting?

A) Increased. B) Decreased. B) Has not changed.

6. What process on the graph characterizes the VG segment?

A) Heating. B) Cooling. B) Melting. D) Hardening.

Graph of melting and solidification of crystalline solids.

Option No. 4 0C

1. What process on the graph characterizes A

segment AB? 400

A) Heating. B) Cooling. B) Melting.

D) Hardening. B C

2. . What process on the graph characterizes

segment BV?

A) Heating. B) Cooling. B) Melting. 200

D) Hardening

3. At what temperature did the process begin?

hardening?

A) 80 0C. B) 350 0С C) 3200С D

D) 450 0С D) 1000 0С

4. How long did it take for the body to harden? 0 10 20 min.

A) 8 min. B) 4 min. B) 12 min.

D) 16 min. D) 7 min.

5. Did the temperature change during curing?

A) Increased. B) Decreased. B) Has not changed.

6. What process on the graph characterizes the VG segment?

A) Heating. B) Cooling. B) Melting. D) Hardening.

III. Lesson summary.

IV. Homework (Differentiated) 5 slide

V. Grading for the lesson.

As the temperature decreases, a substance can change from a liquid to a solid state.

This process is called solidification or crystallization.
When a substance solidifies, the same amount of heat is released, which is absorbed when it melts.

The calculation formulas for the amount of heat during melting and crystallization are the same.

The melting and solidification temperatures of the same substance, if the pressure does not change, are the same.
Throughout the entire crystallization process, the temperature of the substance does not change, and it can simultaneously exist in both liquid and solid states.

LOOK AT THE BOOKSHELF

INTERESTING ABOUT CRYSTALLIZATION

Colored ice?

If you add a little paint or tea leaves to a plastic glass of water, stir and, having obtained a colored solution, wrap the glass on top and expose it to frost, then a layer of ice will begin to form from the bottom to the surface. However, don't expect to get colorful ice!

Where the water began to freeze, there will be an absolutely transparent layer of ice. Its upper part will be colored, and even stronger than the original solution. If the concentration of paint was very high, then a puddle of its solution may remain on the surface of the ice.
The fact is that transparent fresh ice forms in solutions of paint and salts, because... growing crystals displace any extraneous atoms and impurity molecules, trying to build an ideal lattice as long as possible. Only when the impurities have nowhere to go does the ice begin to incorporate them into its structure or leave them in the form of capsules with concentrated liquid. Therefore, sea ice is fresh, and even the dirtiest puddles are covered with transparent and clean ice.

At what temperature does water freeze?

Is it always at zero degrees?
But if you pour boiled water into an absolutely clean and dry glass and place it outside the window in the cold at a temperature of minus 2-5 degrees C, covering it with clean glass and protecting it from direct sunlight, then after a few hours the contents of the glass will cool below zero, but will remain liquid.
If you then open a glass and throw a piece of ice or snow or even just dust into the water, then literally before your eyes the water will instantly freeze, sprouting long crystals throughout the entire volume.

Why?
The transformation of a liquid into a crystal occurs primarily on impurities and inhomogeneities - dust particles, air bubbles, irregularities on the walls of the vessel. Pure water has no centers of crystallization, and it can become supercooled while remaining liquid. In this way it was possible to bring the water temperature to minus 70°C.

How does this happen in nature?

In late autumn, very clean rivers and streams begin to freeze from the bottom. Through the layer of clean water it is clearly visible that the algae and driftwood at the bottom are overgrown with a loose coat of ice. At some point, this bottom ice floats up, and the surface of the water instantly becomes bound by an ice crust.

The temperature of the upper layers of water is lower than the deep ones, and freezing seems to start from the surface. However, clean water freezes reluctantly, and ice primarily forms where there is a suspension of silt and a hard surface - near the bottom.

Downstream from waterfalls and dam spillways, a spongy mass of inland ice often appears, growing in the foaming water. Rising to the surface, it sometimes clogs the entire riverbed, forming so-called jams, which can even dam the river.

Why is ice lighter than water?

Inside the ice there are many pores and spaces filled with air, but this is not the reason that can explain the fact that ice is lighter than water. Ice and without microscopic pores
still has a density less than that of water. It's all about the peculiarities of the internal structure of ice. In an ice crystal, water molecules are located at the nodes of the crystal lattice so that each has four “neighbors.”

Water, on the other hand, does not have a crystalline structure, and the molecules in the liquid are located closer together than in the crystal, i.e. water is denser than ice.
At first, when ice melts, the released molecules still retain the structure of the crystal lattice, and the density of water remains low, but gradually the crystal lattice is destroyed, and the density of water increases.
At a temperature of + 4°C, the density of water reaches a maximum, and then begins to decrease with increasing temperature due to an increase in the speed of thermal movement of molecules.

How does a puddle freeze?

As it cools, the upper layers of water become denser and sink down. Their place is taken by denser water. This mixing occurs until the water temperature drops to +4 degrees Celsius. At this temperature, the density of water is maximum.
With a further decrease in temperature, the upper layers of water can become more compressed, and gradually cooling to 0 degrees, the water begins to freeze.

In autumn, the air temperature at night and during the day is very different, so the ice freezes in layers.
The bottom surface of ice on a freezing puddle is very similar to a cross section of a tree trunk:
concentric rings are visible. The width of the ice rings can be used to judge the weather. Usually the puddle begins to freeze from the edges, because... there is less depth there. The area of ​​the resulting rings decreases as they approach the center.

INTERESTING

That in the pipes of the underground part of buildings, water often freezes not in frost, but in thaw!
This is due to poor thermal conductivity of the soil. Heat passes through the ground so slowly that the minimum temperature in the soil occurs later than at the surface of the earth. The deeper, the greater the delay. Often during frosts the soil does not have time to cool, and only when a thaw sets in on the ground does frost reach underground.

That when water freezes in a sealed bottle, it breaks it. What happens to a glass if you freeze water in it? When water freezes, it will expand not only upward, but also to the sides, and the glass will shrink. This will still lead to the destruction of the glass!

DID YOU KNOW

There is a known case when the contents of a well-chilled bottle of Narzan in the freezer, opened on a hot summer day, instantly turned into a piece of ice.

The metal “cast iron” behaves interestingly, which expands during crystallization. This allows it to be used as a material for the artistic casting of thin lace lattices and small tabletop sculptures. After all, when it hardens, expanding, cast iron fills everything, even the thinnest details of the mold.

In the Kuban in winter they prepare strong drinks - “vymorozki”. To do this, the wine is exposed to frost. The water freezes first, leaving a concentrated alcohol solution. It is drained and the operation is repeated until the desired strength is achieved. The higher the alcohol concentration, the lower the freezing point.

The largest hailstone recorded by humans fell in Kansas, USA. Its weight was almost 700 grams.

Oxygen in a gaseous state at a temperature of minus 183 degrees C turns into liquid, and at a temperature of minus 218.6 degrees C, solid oxygen is obtained from liquid

In the old days, people used ice to store food. Carl von Linde created the first home refrigerator, powered by a steam engine that pumped freon gas through pipes. Behind the refrigerator, the gas in the pipes condensed and turned into liquid. Inside the refrigerator, liquid freon evaporated and its temperature dropped sharply, cooling the refrigerator compartment. Only in 1923, Swedish inventors Balzen von Platen and Karl Muntens created the first electric refrigerator, in which freon turns from a liquid into a gas and takes heat from the air in the refrigerator.

THIS IS YES

Several pieces of dry ice thrown into burning gasoline extinguish the fire.
There is ice that would burn your fingers if you could touch it. It is obtained under very high pressure, at which water turns into a solid state at a temperature well above 0 degrees Celsius.

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Lesson type: combined.

Lesson type: traditional.

Lesson objectives: find out what happens to a substance when it melts and solidifies.

Tasks:

• Educational:
• consolidate existing knowledge on the topic “Structure of Matter”.
• become familiar with the concepts of melting and solidification.
• continue to develop the ability to explain processes from the point of view of the structure of matter.
• explain the concepts of melting and solidification in terms of changes in internal energy
• Educational:
• formation of communicative qualities, communication culture
• developing interest in the subject being studied
• stimulating curiosity and activity in the classroom
• development of performance
• Developmental:
• development of cognitive interest
• development of intellectual abilities
• development of skills to highlight the main thing in the material being studied
• development of skills to generalize studied facts and concepts

Forms of work: frontal, work in small groups, individual.

Learning Tools:

1. Textbook “Physics 8” A.V. Peryshkin § 12, 13, 14.
2. Collection of problems in physics for grades 7-9, A.V. Peryshkin, 610 - 618.
3. Handouts (tables, cards).
4. Presentation.
5. Computer.
6. Illustrations on the topic.

Lesson plan:

1. Organizational moment.
2. Repetition of learned material. Filling the table: solid, liquid, gaseous.
3. Determining the topic of the lesson.
   1. Transition from solid to liquid state of aggregation and vice versa.
   2. Write down the topic of the lesson in your notebook.
4. Learning a new topic:
   1. Determination of the melting point of a substance.
   2. Working with the textbook table “Melting Point”.
   3. Solving the problem.
   4. View the melting and solidification animation.
   5. Working with the Melting and Solidification graph.
   6. Filling out the table: melting, solidification.
5. Consolidation of the studied material.
6. Summing up.
7. Homework.

Literature used:

1. Peryshkin A.V. textbook "Physics 7"
2. Peryshkin A.V. “Collection of problems in physics grades 7 – 9”, Moscow, “Exam”, 2006.
3. V.A. Orlov “Thematic tests in physics grades 7 – 8”, Moscow, “Verbum - M”, 2001.
4. G.N. Stepanova, A.P. Stepanov “Collection of questions and problems in physics grades 5 – 9”, St. Petersburg, “Valeria SPD”, 2001.
5. http://kak-i-pochemu.ru