Presentation on "melting and solidification of crystalline substances." Presentation on the topic "change in the state of aggregation of matter"

“Aggregative state of matter” - Condensation Crystallization. Vaporization. Content. Tcrystallization = tmelting. Aggregate states of matter. Graph of processes of changes in the state of aggregation of a substance. Heating water. Water cooling. Melting. Warming up ice. Three states of matter. Tmelting=const. Processes involving the absorption and release of heat.

“Test “Thermal Phenomena”” - The phenomenon of heat transfer. The story of tea. Examination. Mistress of the house. An ancient aphorism. Convection. Heating curve of a crystalline substance. Solid body cooling. Let's start a story about warmth. Thanks to what method of heat transfer can you warm yourself by the fireplace? Visual gymnastics. Research work.

“Substance and its state” - Even steel steam above it is Observed then. They take the form of a vessel, Oxygen can be solid, and it can also be liquid. IN states of aggregation water will always show us different properties. They don't have their own. The whole world is made of molecules! Liquid, Solid, Molecule – the smallest particle of a substance. Forms and permanent.

“3 states of matter” - Matter. Crystallization. Ice. Examples of processes. Vaporization. States. Arrangement of molecules in liquids. Solve the crossword puzzle. Condensation. The nature of the movement and interaction of particles. The arrangement of molecules in gases. Interesting Facts. Properties of liquids. Questions for the crossword. Properties of solids. Change physical properties substances.

“Three states of matter” - Solid. Physics 7th grade. Why do solids retain their shape? Three states of matter. What does an increase in the temperature of a solid cause? What can you say about the arrangement of molecules when water is heated to boiling? The water evaporated and turned into steam. Questions: Is it possible to fill an open vessel with gas to 50%?

“Thermal phenomena grade 8” - 2. It’s not clear why...? The moon shines, but does not warm? Do you know how people take thermal phenomena into account in everyday life? Have you ever thought about the question: Why is it comfortable to live in a modern house? Is a mother right when she calls her child “My sunshine”? Thermal phenomena in your home. Is it hot in black clothes in summer?

A. S. Pushkin “Eugene Onegin”. In the morning Tatyana saw a whitened yard in the window, Chickens, roofs and a fence, Light patterns on the glass, Trees in winter silver...

Question: What do they represent from the point of view of physics?

There are light patterns on the glass,

Answer: Crystals of frozen water, its solid state.

. E. Baratynsky “Spring”. The streams are noisy! The streams are shining! Roaring, the river carries on the triumphant ridge the ice it raised!

Question: In what

Is water in a state of aggregation?

Answer: Water in liquid and solid state of aggregation.

Snow women are losing weight, melting. It must be their turn. Streams are ringing - spring messengers. And they awaken the ice drift. V. Kremnev.

What changes have occurred in nature?

2. What substance are we talking about?

What happens to the molecules of a substance when the substance is in different states of aggregation?

what is the speed of the molecules of the substance?
what is the distance between the molecules?
what is the relative arrangement of the molecules?

liquid

solid

The transition of a substance from solid to liquid is called melting

The body is given energy

When will the body start to melt?

Do the molecules of a substance change when it melts?

How does the temperature of a substance change when melting?

The transition of a substance from a liquid to a solid state is called crystallization

liquid releases energy

How does the internal energy of a substance change?

How do the energy of molecules and their arrangement change?

When will the body begin to crystallize?

Do the molecules of a substance change during crystallization?

How does the temperature of a substance change during crystallization?

heating

cooling

A physical quantity showing how much heat is needed to convert 1 kg of a crystalline substance taken at the melting point into a liquid of the same temperature is called the specific heat of fusion

Indicated by:

Unit of measurement:

Absorption Q

Selection Q

hardening

melting

t melting = t solidifying

“Reading the chart”

Describe the initial state of the substance

What transformations occur with the substance?

Which parts of the graph correspond to growth temperature of the substance? decrease ?

Which part of the graph corresponds to growth internal energy of matter? decrease ?

“Reading the chart”

At what point in time did the process of melting of the substance begin?

At what point in time did the substance crystallize?

What is the melting point of the substance? crystallization?

How long did it take: heating the solid;

melting of a substance;

liquid cooling?

Check yourself!

1. When a body melts...

a) heat can be both absorbed and released.

b) heat is not absorbed or released.

c) heat is absorbed.

d) heat is released.

2. When a liquid crystallizes...

a) the temperature can either rise or fall.

b) the temperature does not change.

c) the temperature decreases.

d) the temperature rises.

3. When a crystalline body melts...

a) the temperature decreases.

b) the temperature can either rise or fall.

c) the temperature does not change.

d) the temperature rises.

4. During aggregate transformations of a substance, the number of molecules of a substance...

a) does not change.

b) can both increase and decrease.

c) decreases.

d) increases.

Answer: 1-c 2-b 3-c 4-a

Homework:

3. My mood in class. Bad Good Excellent

The transition of a substance from a liquid to a gaseous state is called vaporization

How does the internal energy of a substance change during vaporization?

How do the energy of molecules and their arrangement change?

Do the molecules of a substance change during vaporization?

How does the temperature of a substance change during vaporization?

The transition of a substance from a gaseous state to a liquid state is called condensation

How does the internal energy of a substance change during condensation?

How do the energy of molecules and their arrangement change?

Do the molecules of a substance change during condensation?

Evaporation is the formation of vapor that occurs from the surface of a liquid.

1. What molecules leave the liquid during evaporation?

2. How does the internal energy of a liquid change during evaporation?

3. At what temperature can evaporation occur?

4. How does the mass of a liquid change during evaporation?

Explain why:

Did the water from the saucer evaporate faster?

Has the balance of the scales been disturbed?

after a few days the levels of different fluids became different.

Explain

How will evaporation occur if wind blows over the liquid?

Why does water evaporate faster from a plate than from a bowl?

1. What forms on the walls of a jar if it sits with water for a long time?

2. What is in these bubbles?

3. The surface of the bubbles is also the surface of the liquid. What will happen from the surface inside the bubbles?

Compare processes evaporation and boiling

evaporation

1. In what part of the liquid does vaporization occur?

2. What changes in liquid temperature occur during the process of vaporization?

3. How does the internal energy of a liquid change during vaporization?

4. What determines the speed of the process?

Work of gas and steam during expansion

1. Why does the lid of the kettle sometimes bounce when water is boiling in it?

2. When the steam pushes the lid of the kettle, what does it do?

3. What energy transformations occur when the lid bounces?

Dry ice

When coal is burned, it can be semi-

It’s not hot, but rather cold. To do this, coal is burned in boilers, the resulting smoke is cleaned and captured in it carbon dioxide. It is cooled and compressed to a pressure of 7*10 6 Pa. It turns out liquid carbon dioxide. It is stored in thick-walled cylinders.

When the tap is opened, liquid carbon dioxide expands sharply and cools, turning into hard

I blow carbon dioxide - “dry ice”.

Under the influence of heat, dry ice flakes immediately turn into gas, bypassing the liquid state.

cannot be in a solid state

at t above 0 0 C.

English physicist Bridgman

said that water under pressure p ~

2*10 9 Pa remains firm even with

t = 76 0 C. This is the so-called “go-

hot ice - 5". You can't pick it up

please, about the properties of this variety

The properties of ice were learned indirectly.

“Hot ice” is denser than water (1050

kg/m 3), it sinks in water.

Today, more than 10 different

sights of ice with amazing

Slide 2

What happens to the molecules of a substance when the substance is in different states of aggregation? what is the speed of the molecules of the substance? what is the distance between the molecules? what is the relative arrangement of the molecules? gas liquid solid

Slide 3

The transition of a substance from a solid to a liquid state is called melting. Energy is imparted to the body. How does the energy of molecules and their arrangement change? How does the internal energy of a substance change? Do the molecules of a substance change when it melts? How does the temperature of a substance change when melting? When will the body start to melt?

Slide 4

The transition of a substance from a liquid to a solid state is called crystallization; the liquid gives up energy. How does the energy of molecules and their arrangement change? How does the internal energy of a substance change? Do the molecules of a substance change during crystallization? How does the temperature of a substance change during crystallization? When will the body begin to crystallize?

Slide 5

melting heating solidification cooling A physical quantity showing how much heat is needed to convert 1 kg of a crystalline substance taken at the melting point into a liquid of the same temperature, called the specific heat of fusion Designated by: Unit of measurement: Absorption Q Release Q tmelting = t solidification 

Slide 6

“Reading the graph” Describe the initial state of the substance. What transformations occur in the substance? Which parts of the graph correspond to an increase in the temperature of the substance? decrease? Which part of the graph corresponds to the increase in the internal energy of the substance? decrease? 1 2 3 4

Slide 7

“Reading the graph” At what point in time did the process of melting of the substance begin? How long did it take: heating the solid; melting of a substance; liquid cooling? At what point in time did the substance crystallize? What is the melting point of the substance? crystallization?

Slide 8

Check yourself! 1. When a body melts... a) heat can be both absorbed and released. b) heat is not absorbed or released. c) heat is absorbed. d) heat is released. 2. When a liquid crystallizes... a) the temperature can either increase or decrease. b) the temperature does not change. c) the temperature decreases. d) the temperature rises. 3. When a crystalline body melts... a) the temperature decreases. b) the temperature can either rise or fall. c) the temperature does not change. d) the temperature rises. 4. During aggregate transformations of a substance, the number of molecules of a substance... a) does not change. b) can both increase and decrease. c) decreases. d) increases. Answer: 1-c 2-b 3-c 4-a

Slide 9

The transition of a substance from a liquid to a gaseous state is called vaporization. How does the energy of molecules and their arrangement change? How does the internal energy of a substance change during vaporization? Do the molecules of a substance change during vaporization? How does the temperature of a substance change during vaporization?

Slide 10

The transition of a substance from a gaseous state to a liquid state is called condensation. How does the energy of molecules and their arrangement change? How does the internal energy of a substance change during condensation? Do the molecules of a substance change during condensation?

Slide 11

Evaporation is the formation of vapor that occurs from the surface of a liquid 1. What molecules leave the liquid during evaporation? 2. How does the internal energy of a liquid change during evaporation? 3. At what temperature can evaporation occur? 4. How does the mass of a liquid change during evaporation?

Slide 12

Explain why:

Did the water from the saucer evaporate faster? Has the balance of the scales been disturbed? after a few days the levels of different fluids became different.

Slide 13

Explain

How will evaporation occur if wind blows over the liquid? Why does water evaporate faster from a plate than from a bowl?

Slide 14

boiling

1. What forms on the walls of a jar if it sits with water for a long time? boiling 2. What is in these bubbles? 3. The surface of the bubbles is also the surface of the liquid. What will happen from the surface inside the bubbles?

Slide 15

Compare the processes of evaporation and boiling

1. In what part of the liquid does vaporization occur? 2. What changes in liquid temperature occur during the process of vaporization? 3. How does the internal energy of a liquid change during vaporization? 4. What determines the speed of the process? evaporation boiling

Slide 16

Work of gas and steam during expansion

1. Why does the lid of the kettle sometimes bounce when water is boiling in it? ICE 2. When the steam pushes the lid of the kettle, what does it do? 3. What energy transformations occur when the lid bounces?

Slide 17

What kind of ice is there? Hot ice We are accustomed to thinking that water cannot be in a solid state at temperatures above 0 0C. The English physicist Bridgman showed that water under pressure p ~ 2*109 Pa remains solid even at t = 76 0C. This is the so-called “hot ice - 5”. It is impossible to pick it up; we learned about the properties of this type of ice indirectly. “Hot ice” is denser than water (1050 kg/m3), it sinks in water. Today, more than 10 varieties of ice with amazing qualities are known. Dry ice When burning coal, you can get not heat, but, on the contrary, cold. To do this, coal is burned in boilers, the resulting smoke is purified and carbon dioxide is captured in it. It is cooled and compressed to a pressure of 7*106 Pa. The result is liquid carbon dioxide. It is stored in thick-walled cylinders. When the tap is opened, liquid carbon dioxide expands sharply and cools, turning into solid carbon dioxide - “dry ice”. Under the influence of heat, dry ice flakes immediately turn into gas, bypassing the liquid state. Can the named varieties of ice be considered a new state of aggregation of matter?

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The ideal gas model, used in the molecular kinetic theory of gases, makes it possible to describe the behavior of rarefied real gases at sufficiently high temperatures And low pressures. When deriving the equation of state for an ideal gas, the sizes of molecules and their interactions with each other are neglected. An increase in pressure leads to a decrease in the average distance between molecules, so it is necessary to take into account the volume of molecules and the interaction between them. Thus, 1 m 3 of gas under normal conditions contains 2.68 × 10 25 molecules, occupying a volume of approximately 10 –4 m 3 (the radius of the molecule is approximately 10 –10 m), which can be neglected in comparison with the volume of gas (1 m 3 . At a pressure of 500 MPa (1 atm = 101.3 kPa), the volume of molecules will already be half the total volume of the gas. Thus, at high pressures and low temperatures, the specified ideal gas model is unsuitable.

By revising real gases- gases whose properties depend on the interaction of molecules must be taken into account forces of intermolecular interaction. They appear at distances of £ 10–9 m and quickly decrease with increasing distance between the molecules. Such forces are called short-acting.

As ideas about the structure of the atom and quantum mechanics developed, it was found that substances simultaneously act between molecules attractive and repulsive forces. In Fig. 88, A the qualitative dependence of the forces of intermolecular interaction on distance is given r between molecules, where F about and F n are the repulsive and attractive forces, respectively, a F- their resultant. Repulsive forces are considered positive, and the forces of mutual attraction - negative.

On distance r=r 0 resultant force F= 0, those. the forces of attraction and repulsion balance each other. So the distance r 0 corresponds to the equilibrium distance between the molecules at which they would be in the absence of thermal motion. At r< r 0 repulsive forces prevail ( F> 0), at r>r 0 - forces of attraction ( F<0). At distances r> 10 –9 m there are practically no intermolecular interaction forces ( F®0).

Elementary work dA strength F with increasing distance between molecules by d r occurs by reducing the mutual potential energy of the molecules, i.e.

(60.1)

From the analysis of the qualitative dependence of the potential energy of interaction of molecules on the distance between them (Fig. 88, b) it follows that if the molecules are located at a distance from each other at which intermolecular interaction forces do not act ( r®¥), then P=0. With the gradual approach of molecules between them, attractive forces appear ( F<0), которые совершают положительную работу (dA=F d r> 0).Then, according to (60.1), the potential interaction energy decreases, reaching a minimum at r=r 0 . At r<r 0 decreasing r repulsive forces ( F>0) increase sharply and the work done against them is negative ( dA=F d r<0). Потенциальная энергия начинает тоже резко возрастать и становится положительной. Из данной потенциальной кривой следует, что система из двух взаимодействующих молекул в состоянии устойчивого равновесия (r=r 0) has minimal potential energy.

The criterion for various states of aggregation of a substance is the ratio between the values of P min and kT. P min - the lowest potential energy of interaction between molecules - determines the work that needs to be done against the forces of attraction in order to separate molecules that are in equilibrium ( r=r 0); kT determines twice the average energy per degree of freedom of chaotic (thermal) motion of molecules.

If P min<<kT, then the substance is in a gaseous state, since the intense thermal movement of molecules prevents the connection of molecules that have come close to a distance r 0, i.e. the probability of the formation of aggregates from molecules is quite small. If P min >> kT, then the substance is in a solid state, since the molecules, being attracted to each other, cannot move away over significant distances and fluctuate around equilibrium positions determined by the distance r 0 . If P min » kT, then the substance is in a liquid state, since as a result of thermal motion the molecules move in space, exchanging places, but not diverging to a distance exceeding r 0 .

Thus, any substance, depending on the temperature, can be in a gaseous, liquid or solid state of aggregation, and the temperature of transition from one state of aggregation to another depends on the value of P min for a given substance. For example, for inert gases P min is small, but for metals it is large, therefore at ordinary (room) temperatures they are in gaseous and solid states, respectively.

Basic principles of molecular kinetic theory:

All substances are made up of molecules, and molecules are made up of atoms,

atoms and molecules are in constant motion,

· there are forces of attraction and repulsion between molecules.

IN gases molecules move chaotically, the distances between molecules are large, molecular forces are small, the gas occupies the entire volume provided to it.

IN liquids molecules are arranged in an orderly manner only at short distances, and at large distances the order (symmetry) of the arrangement is violated - “short-range order”. The forces of molecular attraction keep molecules close together. The movement of molecules is “jumping” from one stable position to another (usually within one layer. This movement explains the fluidity of a liquid. A liquid has no shape, but has volume.

Solids are substances that retain their shape, divided into crystalline and amorphous. Crystalline solids bodies have a crystal lattice, in the nodes of which there may be ions, molecules or atoms. They oscillate relative to stable equilibrium positions.. Crystal lattices have a regular structure throughout the entire volume - “long-range order” of arrangement.

Amorphous bodies retain their shape, but do not have a crystal lattice and, as a result, do not have a pronounced melting point. They are called frozen liquids, since they, like liquids, have a “short-range” order of molecular arrangement.

The vast majority of substances expand when heated. This is easily explained from the perspective of the mechanical theory of heat, since when heated, the molecules or atoms of a substance begin to move faster. In solids, atoms begin to vibrate with greater amplitude around their average position in the crystal lattice, and they require more free space. As a result, the body expands. Likewise, liquids and gases, for the most part, expand with increasing temperature due to an increase in the speed of thermal movement of free molecules ( cm. Boyle-Marriott's law, Charles's law, Equation of state of an ideal gas).

The basic law of thermal expansion states that a body with linear size L in the corresponding dimension when its temperature increases by Δ T expands by an amount Δ L, equal to:

Δ L = αLΔ T

Where α - so-called coefficient of linear thermal expansion. Similar formulas are available for calculating changes in area and volume of a body. In the simplest case presented, when the coefficient of thermal expansion does not depend on either the temperature or the direction of expansion, the substance will expand uniformly in all directions in strict accordance with the above formula.

For engineers, thermal expansion is a vital phenomenon. When designing a steel bridge across a river in a city with a continental climate, it is impossible not to take into account possible temperature changes ranging from -40°C to +40°C throughout the year. Such differences will cause a change in the total length of the bridge up to several meters, and so that the bridge does not heave in the summer and does not experience powerful tensile loads in the winter, designers compose the bridge from separate sections, connecting them with special thermal buffer joints, which are rows of teeth that engage, but are not rigidly connected, that close tightly in the heat and diverge quite widely in the cold. On a long bridge there may be quite a few of these buffers.

However, not all materials, especially crystalline solids, expand uniformly in all directions. And not all materials expand equally at different temperatures. The most striking example of the latter kind is water. When water cools, it first contracts, like most substances. However, from +4°C to the freezing point of 0°C, water begins to expand when cooled and contract when heated (from the point of view of the above formula, we can say that in the temperature range from 0°C to +4°C the coefficient of thermal expansion water α takes a negative value). It is thanks to this rare effect that the earth's seas and oceans do not freeze to the bottom even in the most severe frosts: water colder than +4°C becomes less dense than warmer water and floats to the surface, displacing water with a temperature above +4°C to the bottom.

The fact that ice has a specific density lower than the density of water is another (although not related to the previous one) anomalous property of water, to which we owe the existence of life on our planet. If not for this effect, the ice would sink to the bottom of rivers, lakes and oceans, and they, again, would freeze to the bottom, killing all living things.

34. Ideal gas laws. Equation of state of an ideal gas (Mendeleev-Clapeyron). Avogadro's and Dalton's laws.

The molecular kinetic theory uses the ideal gas model, in which it is considered:
1) the intrinsic volume of gas molecules is negligible compared to the volume of the container;
2) there are no interaction forces between gas molecules;
3) collisions of gas molecules with each other and with the walls of the vessel are absolutely elastic.

Real gases at low pressures and high temperatures are close in their properties to an ideal gas.

Let us consider the empirical laws that describe the behavior of ideal gases.

1. Boyle–Mariotte law: for a given mass of gas at a constant temperature, the product of the gas pressure and its volume is a constant:

pV=const at T=const, m=const (7)

A process occurring at a constant temperature is called isothermal. A curve depicting the relationship between the values p and V, which characterize the properties of a substance at a constant temperature, is called an isotherm. Isotherms are hyperbolas located higher, the higher the temperature at which the process occurs (Fig. 1).

Rice. 1. Dependence of ideal gas pressure on volume at constant temperature

2. Gay-Lussac’s law: the volume of a given mass of gas at constant pressure changes linearly with temperature:

V=V 0 (1+αt) at p=const, m=const (8)

Here t is the temperature on the Celsius scale, V 0 is the volume of gas at 0 o C, α = (1/273) K -1 is the temperature coefficient of volumetric expansion of the gas.

A process occurring at constant pressure and constant gas mass is called isobaric. During an isobaric process for a gas of a given mass, the ratio of volume to temperature is constant:

On the diagram in coordinates (V,t), this process is depicted by a straight line called an isobar (Fig. 2).

Rice. 2. Dependence of the volume of an ideal gas on temperature at constant pressure

3. Charles’s law: the pressure of a given mass of gas at a constant volume changes linearly with temperature:

p=p 0 (1+αt) at p=const, m=const (9)

Here t is the temperature on the Celsius scale, p 0 is the gas pressure at 0 o C, α = (1/273) K -1 is the temperature coefficient of volumetric expansion of the gas.

A process occurring at a constant volume and constant mass of gas is called isochoric. During an isochoric process for a gas of a given mass, the ratio of pressure to temperature is constant:

On the diagram in coordinates this process is depicted by a straight line called an isochore (Fig. 3).

Rice. 3. Dependence of ideal gas pressure on temperature at constant volume

By introducing the thermodynamic temperature T in formulas (8) and (9), the laws of Gay-Lussac and Charles can be given a more convenient form:

V=V 0 (1+αt)=V 0 =V 0 αT (10)
p=p 0 (1+αt)=p 0 =p 0 αT (11)

Avogadro's law: moles of any gases at the same temperature and pressure occupy the same volumes.

So, under normal conditions, one mole of any gas occupies a volume of 22.4 m -3. At the same temperature and pressure, any gas contains the same number of molecules per unit volume.

Under normal conditions, 1 m 3 of any gas contains a number of particles called the Loschmidt number:

N L =2.68·10 25 m -3.

Dalton's law: the pressure of a mixture of ideal gases is equal to the sum of the partial pressures p 1 , p 2 ,..., p n of the gases included in it:

p=p 1 +p 2 +....+p n

Partial pressure is the pressure that a gas included in a gas mixture would create if it occupied a volume equal to the volume of the mixture at the same temperature.

Melting heating solidifying cooling A physical quantity showing how much heat is needed to transform 1 kg of a crystalline substance taken at the melting point into a liquid of the same temperature, called the specific heat of fusion Designated by: Unit of measurement: Absorption Q Release Q t melting = t solidification

Reading the graph Describe the initial state of the substance What transformations occur in the substance? Which parts of the graph correspond to an increase in the temperature of the substance? decrease? Which part of the graph corresponds to the increase in the internal energy of the substance? decrease?

Reading the graph At what point in time did the process of melting the substance begin? How long did it take: heating the solid; melting of a substance; liquid cooling? At what point in time did the substance crystallize? What is the melting point of the substance? crystallization?

Compare the processes of evaporation and boiling 1. In what part of the liquid does vaporization occur? 2. What changes in liquid temperature occur during the process of vaporization? 3. How does the internal energy of a liquid change during vaporization? 4. What determines the speed of the process? evaporationboiling

Hot ice We are accustomed to thinking that water cannot be in a solid state at t above 0 0 C. And the English physicist Bridgman showed that water under pressure p ~ 2*10 9 Pa remains solid even at t = 76 0 C This is the so-called “hot ice - 5”. It is impossible to pick it up; we learned about the properties of this type of ice indirectly. “Hot ice” is denser than water (1050 kg/m3), it sinks in water. Today, more than 10 varieties of ice with amazing qualities are known. Dry ice When burning coal, you can get not heat, but, on the contrary, cold. To do this, coal is burned in boilers, the resulting smoke is purified and carbon dioxide is captured in it. It is cooled and compressed to a pressure of 7*10 6 Pa. The result is liquid carbon dioxide. It is stored in thick-walled cylinders. When the tap is opened, liquid carbon dioxide expands sharply and cools, turning into solid carbon dioxide - “dry ice”. Under the influence of heat, dry ice flakes immediately turn into gas, bypassing the liquid state.