Any substance consists of molecules, and its physical properties depend on how the molecules are ordered and how they interact with each other. V ordinary life we observe three aggregate states of matter - solid, liquid and gaseous.

For example, water can be in solid (ice), liquid (water), and gaseous (vapor) states.

Gas expands until it fills the entire volume allocated to it. If we consider the gas on molecular level, we will see molecules randomly tossing and colliding with each other and with the walls of the vessel, which, however, practically do not interact with each other. If the volume of the vessel is increased or decreased, the molecules will be evenly redistributed in the new volume.

Unlike a gas at a given temperature, it occupies a fixed volume, however, it also takes the form of a vessel to be filled - but only below its surface level. At the molecular level, a liquid is most easily represented in the form of spherical molecules, which, although they are in close contact with each other, have the freedom to roll relative to each other, like round beads in a jar. Pour liquid into the vessel - and the molecules will quickly spread and fill the lower part of the vessel volume, as a result, the liquid will take its shape, but will not spread to the full volume of the vessel.

Solid has its own shape, does not spread over the volume of the containerand does not take its form. At the microscopic level, atoms attach to each other. chemical bonds, and their position relative to each other is fixed. At the same time, they can form both rigid ordered structures - crystal lattices - and a disorderly heap - amorphous bodies (this is exactly the structure of polymers, which look like tangled and stuck together pasta in a bowl).

Above, three classical states of aggregation were described. There is, however, a fourth state, which physicists are inclined to attribute to the number of aggregates. This is a plasma state. Plasma is characterized by partial or complete stripping of electrons from their atomic orbits, while the free electrons themselves remain inside the substance.

We can observe the change in the aggregate states of matter with our own eyes in nature. Water from the surface of reservoirs evaporates and clouds form. This is how the liquid turns into gas. In winter, water in reservoirs freezes, turning into a solid state, and in spring it melts again, turning back into a liquid. What happens to the molecules of a substance when it passes from one state to another? Are they changing? For example, are ice molecules different from vapor molecules? The answer is unequivocal: no. The molecules remain exactly the same. Their kinetic energy changes, and, accordingly, the properties of the substance.

The energy of the vapor molecules is large enough to scatter in different directions, and when cooled, the vapor condenses into a liquid, and the molecules still have enough energy for almost free movement, but not enough to break away from the attraction of other molecules and fly away. With further cooling, the water freezes, becoming a solid, and the energy of the molecules is no longer enough even for free movement inside the body. They vibrate about one place, held by the forces of attraction of other molecules.

The main general education

UMK line A.V. Peryshkin. Physics (7-9)

Introduction: state of aggregation of matter

State of aggregation - state of a substance that has certain properties: the ability to maintain shape and volume, have long-range or short-range order, and others. When it changes aggregate state of matter there is a change physical properties, as well as density, entropy and free energy.

How and why do these amazing transformations take place? To understand this, remember that everything around consists of... Atoms and molecules of various substances interact with each other, and it is the connection between them that determines what is the state of aggregation of the substance.

There are four types of aggregate substances:

gaseous

It seems that chemistry reveals its secrets to us in these amazing transformations. However, it is not. The transition from one state of aggregation to another, as well as diffusion, refer to physical phenomena, since in these transformations there are no changes in the molecules of the substance and their chemical composition is preserved.

Gaseous state

At the molecular level, gas is a chaotically moving molecules that collide with the walls of the vessel and with each other, which practically do not interact with each other. Since the gas molecules are not connected with each other, the gas fills the entire volume provided to it, interacting and changing direction only when it hits each other.

Unfortunately, it is impossible to see gas molecules with the naked eye and even with the help of a light microscope. However, the gas can be touched. Of course, if you just try to catch gas molecules flying around in the palm of your hand, then you will not succeed. But surely everyone saw (or did it themselves) how someone inflated the tire of a car or bicycle, and from soft and wrinkled it became inflated and elastic. And the apparent "weightlessness" of gases will refute the experiment described on page 39 of the textbook "Chemistry Grade 7" edited by O.S. Gabrielyan.

This happens because the closed limited volume of the tire gets a large number of molecules, which becomes cramped, and they begin to strike more often against each other and against the walls of the tire, and as a result, the total effect of millions of molecules on the walls is perceived by us as pressure.

But if the gas occupies the entire volume provided to it, why then does it not fly into space and spread throughout the entire universe, filling interstellar space? Does it mean that something is still holding and restricting gases by the planet's atmosphere?

Quite right. And this - gravity... In order to break away from the planet and fly away, the molecules need to develop a speed exceeding the "escape speed" or the second space speed, and the vast majority of molecules move much more slowly.

Then the following question arises: why the gas molecules do not fall to the ground, but continue to fly? It turns out that thanks to solar energy, air molecules have a solid reserve of kinetic energy, which allows them to move against the forces of gravity.

The collection contains questions and tasks of various orientations: calculated, qualitative and graphic; technical, practical and historical. Tasks are distributed by topic in accordance with the structure of the textbook "Physics. Grade 9 "authors A. V. Peryshkin, E. M. Gutnik and allow you to implement the requirements stated by the Federal State Educational Standard for metasubject, personal results learning.

Liquid state

With increasing pressure and / or decreasing temperature, gases can be converted to a liquid state. At the dawn of the nineteenth century English physicist and chemist Michael Faraday succeeded in liquidizing chlorine and carbon dioxide compressing them at very low temperatures. However, some of the gases did not succumb to scientists at that time, and, as it turned out, it was not a lack of pressure, but the inability to reduce the temperature to the required minimum.

A liquid, unlike a gas, occupies a certain volume, but it also takes the form of a container to be filled below surface level. The liquid can be visualized as round beads or cereals in a jar. Liquid molecules are in close interaction with each other, but move freely relative to each other.

If a drop of water remains on the surface, after a while it will disappear. But we remember that thanks to the law of conservation of mass-energy, nothing disappears and does not disappear without a trace. The liquid will evaporate, i.e. will change its state of aggregation to gaseous.

Evaporation - this is the process of transformation of the state of aggregation of a substance, in which molecules, whose kinetic energy exceeds the potential energy of intermolecular interaction, rise from the surface of a liquid or solid.

Evaporation from the surface of solids is called sublimation or sublimation... Most in a simple way Observe sublimation is the use of mothballs to fight moths. If you smell a liquid or solid, then evaporation is occurring. After all, the nose just catches the aromatic molecules of the substance.

Fluids surround a person everywhere. The properties of liquids are also familiar to everyone - they are viscosity, fluidity. When talking about the shape of a liquid, many say that the liquid does not have a specific shape. But this only happens on Earth. Thanks to the force of gravity, a drop of water is deformed.

However, many have seen how astronauts catch water balls of different sizes in zero gravity. In the absence of gravity, the liquid takes the form of a ball. And the surface tension force provides the liquid with a spherical shape. Bubbles are a great way to get to know the forces of surface tension on Earth.

Another property of a liquid is viscosity. Viscosity depends on pressure, chemical composition and temperature. Most fluids obey Newton's law of viscosity, discovered in the 19th century. However, there are a number of liquids with high viscosity, which, under certain conditions, begin to behave like solids and do not obey Newton's law of viscosity. Such solutions are called non-Newtonian fluids. The simplest example of a non-Newtonian liquid is a suspension of starch in water. If you act on a non-Newtonian fluid by mechanical forces, the fluid will begin to take on the properties of solids and behave like a solid.

Solid state

If in a liquid, unlike a gas, the molecules no longer move chaotically, but around certain centers, then in the solid state of aggregation of matter the atoms and molecules have a clear structure and look like the built soldiers on the parade. And thanks to the crystal lattice solids occupy a certain volume and have a constant shape.

Under certain conditions, substances in the aggregate state of a liquid can turn into a solid, and solid bodies, on the contrary, melt and turn into a liquid when heated.

This happens because when heated, the internal energy increases, respectively, the molecules begin to move faster, and when the melting temperature is reached, the crystal lattice begins to collapse and the state of aggregation of the substance changes. Most crystalline bodies the volume increases during melting, but there are exceptions, for example, ice, cast iron.

Depending on the type of particles that form the crystal lattice of a solid, the following structure is distinguished:

molecular,

metal.

Some substances change of state of aggregation happens easily, as, for example, near water; other substances require special conditions (pressure, temperature). But in modern physics scientists distinguish another independent state of matter - plasma.

Plasma - ionized gas with the same density of both positive and negative charges... In living nature, plasma is in the sun, or during a flash of lightning. northern Lights and even the familiar bonfire, which warms us with its warmth during outings to nature, also refers to plasma.

Artificially created plasma adds brightness to any city. The neon signs are just low-temperature plasma in glass tubes. The fluorescent lamps we are used to are also filled with plasma.

Plasma is divided into low-temperature - with an ionization degree of about 1% and a temperature of up to 100 thousand degrees, and high-temperature - ionization of about 100% and a temperature of 100 million degrees (this is the state of plasma in stars).

Low-temperature plasma in fluorescent lamps familiar to us is widely used in everyday life.

High-temperature plasma is used in thermonuclear fusion reactions and scientists do not lose hope of using it as a replacement for atomic energy, but control in these reactions is very difficult. And the uncontrolled thermonuclear reaction has established itself as a weapon of colossal power when the USSR tested a thermonuclear bomb on August 12, 1953.

Buy

To check the assimilation of the material, we offer a small test.

1. What does not apply to aggregate states:

liquid

light +

2. The viscosity of Newtonian fluids is subject to:

Boyle-Mariotte law

Archimedes' law

Newton's law of viscosity +

3. Why does the Earth's atmosphere not fly into outer space:

because gas molecules cannot develop the second cosmic speed

because gas molecules are affected by gravity +

both answers are correct

4. What does not apply to amorphous substances:

• sealing wax

• iron +

5.When cooling, the volume increases in:

• ice +

In order to understand what the state of aggregation of a substance is, remember or imagine yourself in the summer near a river with ice cream in your hands. Great picture, isn't it?

So, in this idyll, in addition to getting pleasure, you can also carry out physical observation. Pay attention to the water. In the river it is liquid, in the composition of ice cream in the form of ice it is solid, and in the sky in the form of clouds it is gaseous. That is, it is simultaneously in three different states. In physics, this is called the state of aggregation of matter. There are three states of aggregation - solid, liquid and gaseous.

Change in aggregate states of matter

We can observe the change in the aggregate states of matter with our own eyes in nature. Water from the surface of reservoirs evaporates and clouds form. This is how the liquid turns into gas. In winter, water in reservoirs freezes, turning into a solid state, and in spring it melts again, turning back into a liquid. What happens to the molecules of a substance when it passes from one state to another? Are they changing? For example, are ice molecules different from vapor molecules? The answer is unequivocal: no. The molecules remain exactly the same. Their kinetic energy changes, and, accordingly, the properties of the substance. The energy of the vapor molecules is large enough to scatter in different directions, and when cooled, the vapor condenses into a liquid, and the molecules still have enough energy for almost free movement, but not enough to break away from the attraction of other molecules and fly away. With further cooling, the water freezes, becoming a solid, and the energy of the molecules is no longer enough even for free movement inside the body. They vibrate about one place, held by the forces of attraction of other molecules.

The nature of the movement and state of molecules in various states of aggregation can be reflected in the following table:

Processes in which there is a change in the state of aggregation of substances, six in total.

The transition of a substance from a solid state to a liquid is called melting, the reverse process is crystallization... When a substance passes from a liquid to a gas, it is called vaporization, from gas to liquid - condensation... The transition from a solid state directly to a gas, bypassing a liquid state, is called sublimation, the reverse process is desublimation.

• 1. Melting
• 2. Crystallization
• 3. Steam generation
• 4. Condensation
• 5. Sublimation
• 6. Desublimation

Examples of all these transitions we have seen more than once in our life. Ice melts to form water, water evaporates to form steam. V reverse side steam, condensing, goes back into water, and water, freezing, becomes ice. And if you think that you do not know the processes of sublimation and desublimation, then do not rush to conclusions. The smell of any solid body is nothing more than sublimation. Some of the molecules are ejected from the body, forming a gas, which we can smell. And an example of the reverse process is the patterns on glass in winter, when vapor in the air, freezing, settles on the glass and forms bizarre patterns.

Definition 1

Aggregate states of matter(from Lat. “aggrego” means “attach”, “bind”) - these are states of the same substance in solid, liquid and gaseous form.

During the transition from one state to another, a jump-like change in energy, entropy, density and other properties of matter is observed.

Solid and liquid bodies

Solid bodies- these are bodies that are distinguished by the constancy of their shape and volume.

In solids, intermolecular distances are small, and the potential energy of molecules can be compared with kinetic energy.

Solids are divided into 2 types:

1. Crystalline;
2. Amorphous.

Only crystalline bodies are in a state of thermodynamic equilibrium. Amorphous bodies, in fact, are metastable states, which are similar in structure to nonequilibrium, slowly crystallizing liquids. An overly slow crystallization process takes place in an amorphous body, a process of gradual transformation of a substance into a crystalline phase. The difference between a crystal and an amorphous solid is, first of all, in the anisotropy of its properties. The properties of a crystalline body are determined depending on the direction in space. Various processes(for example, thermal conductivity, electrical conductivity, light, sound) propagate in different directions of a solid in different ways. But amorphous bodies (for example, glass, resins, plastics) are isotropic, like liquids. The difference between amorphous bodies and liquids lies only in the fact that the latter are fluid, static shear deformations do not occur in them.

Crystalline bodies have the correct molecular structure... It is due to the correct structure that the crystal has anisotropic properties. The correct arrangement of the crystal atoms creates the so-called crystal lattice. In different directions, the arrangement of atoms in the lattice is different, which leads to anisotropy. Atoms (ions or whole molecules) in the crystal lattice perform random vibrational motion near the middle positions, which are considered as the nodes of the crystal lattice. The higher the temperature, the higher the vibration energy, and hence the average vibration amplitude. The size of the crystal is determined depending on the vibration amplitude. An increase in the amplitude of vibrations leads to an increase in body size. This explains the thermal expansion of solids.

Definition 3

Liquid bodies- these are bodies that have a certain volume, but do not have an elastic shape.

For substance in liquid state strong intermolecular interaction and low compressibility are characteristic. The liquid takes an intermediate position between a solid and a gas. Liquids, like gases, have isotopic properties. In addition, the liquid has the property of flowability. In it, as in gases, there is no tangential stress (shear stress) of bodies. Liquids are heavy, that is, their specific gravity can be compared with the specific gravity of solids. Near crystallization temperatures, their heat capacity and other thermal properties are close to the corresponding properties of solids. In liquids, the correct arrangement of atoms is observed to a given degree, but only in small areas. Here, the atoms also oscillate around the nodes of the quasicrystalline cell, however, in contrast to the atoms of a solid, they periodically jump from one site to another. As a result, the motion of atoms will be very complex: vibrational, but at the same time the center of vibrations moves in space.

Gas- this is a state of matter in which the distances between molecules are enormous.

The forces of interaction between molecules at low pressures can be neglected. Gas particles fill the entire volume that is provided for the gas. Gases are considered as highly superheated or unsaturated vapors. A special type of gas is plasma (partially or fully ionized gas, in which the densities of positive and negative charges are almost the same). That is, plasma is a gas of charged particles that interact with each other using electrical forces at a great distance, but do not have a near and far location of particles.

As you know, substances are capable of passing from one state of aggregation to another.

Definition 5

Evaporation Is a process of changing the state of aggregation of a substance, in which molecules fly out from the surface of a liquid or solid body, the kinetic energy of which transforms the potential energy of the interaction of molecules.

Evaporation is a phase transition. When evaporated, part of the liquid or solid is converted to vapor.

Definition 6

A substance in a gaseous state that is in dynamic equilibrium with a liquid is called saturated ferry... In this case, the change in the internal energy of the body is equal to:

∆ U = ± m r (1),

where m is the body weight, r is the specific heat of vaporization (D l / k g).

Definition 7

Condensation is the reverse process of vaporization.

The change in internal energy is calculated by the formula (1).

Definition 8

Melting Is a process of transformation of a substance from a solid state into a liquid state, a process of changing the state of aggregation of a substance.

When a substance is heated, its internal energy grows, therefore, the rate of thermal movement of molecules increases. When a substance reaches its melting point, the crystal lattice of a solid is destroyed. The bonds between the particles are also destroyed, and the interaction energy between the particles increases. The heat that is transferred to the body is used to increase the internal energy of the given body, and part of the energy is spent on performing work on changing the volume of the body when it melts. In many crystalline bodies, the volume increases during melting, but there are exceptions (for example, ice, cast iron). Amorphous bodies do not have a specific melting point. Melting is a phase transition characterized by an abrupt change in heat capacity at the melting temperature. The melting point depends on the substance and remains unchanged during the process. Then the change in the internal energy of the body is equal to:

∆ U = ± m λ (2),

where λ is the specific heat of fusion (D liquid / kg g).

Definition 9

Crystallization is the reverse process of melting.

The change in internal energy is calculated by the formula (2).

The change in the internal energy of each body of the system during heating or cooling is calculated by the formula:

∆ U = m c ∆ T (3),

where c is the specific heat capacity of the substance, D l k g K, △ T is the change in body temperature.

Definition 10

When considering the transformations of substances from one state of aggregation to others, one cannot do without the so-called heat balance equations: the total amount of heat released in a heat-insulated system is equal to the amount of heat (total) that is absorbed in this system.

Q 1 + Q 2 + Q 3 +. ... ... + Q n = Q "1 + Q" 2 + Q "3 +... + Q" k.

In fact, the heat balance equation is the law of conservation of energy for heat transfer processes in thermally insulated systems.

Example 1

The insulated vessel contains water and ice with a temperature of t i = 0 ° C. The mass of water m υ and ice m i are respectively equal to 0.5 kg and 60 g. Water vapor with a mass of m p = 10 g is injected into the water at a temperature of t p = 100 ° C. What will be the temperature of the water in the vessel after thermal equilibrium is established? In this case, the heat capacity of the vessel does not need to be taken into account.

Picture 1

Solution

Let us determine what processes are carried out in the system, what aggregate states of matter we observed and what we received.

Water vapor condenses, giving off heat.

Thermal energy is used to melt the ice and, possibly, to heat the water available and obtained from the ice.

First of all, let's check how much heat is released during the condensation of the existing mass of steam:

Q p = - r m p; Q p = 2, 26 · 10 6 · 10 - 2 = 2, 26 · 10 4 (D g),

here, from the reference materials, we have r = 2, 26 · 10 6 J l k g - the specific heat of vaporization (it is also used for condensation).

The following amount of heat is required to melt the ice:

Q i = λ m i Q i = 6 10 - 2 3, 3 10 5 ≈ 2 10 4 (D g),

here, from the reference materials, we have λ = 3, 3 · 10 5 J l k g - the specific heat of melting of ice.

It turns out that the steam gives off more heat than necessary, only to melt the existing ice, which means that we write the heat balance equation as follows:

r m p + c m p (T p - T) = λ m i + c (m υ + m i) (T - T i).

Heat is released during the condensation of steam of mass m p and cooling of water formed from the steam from the temperature T p to the desired T. Heat is absorbed by melting ice of mass m i and heating water of mass m υ + m i from temperature T i to T. We denote T - T i = ∆ T for the difference T p - T we obtain:

T p - T = T p - T i - ∆ T = 100 - ∆ T.

The heat balance equation will be:

r m p + c m p (100 - ∆ T) = λ m i + c (m υ + m i) ∆ T; c (m υ + m i + m p) ∆ T = r m p + c m p 100 - λ m i; ∆ T = r m p + c m p 100 - λ m i c m υ + m i + m p.

Let's make calculations taking into account the fact that the heat capacity of water is tabular

c = 4.2 10 3 J l k g K, T p = tp + 273 = 373 K, T i = ti + 273 = 273 K: ∆ T = 2, 26 10 6 10 - 2 + 4, 2 · 10 3 · 10 - 2 · 10 2 - 6 · 10 - 2 · 3, 3 · 10 5 4, 2 · 10 3 · 5, 7 · 10 - 1 ≈ 3 (K),

then T = 273 + 3 = 276 K

Answer: The temperature of the water in the vessel after the establishment of thermal equilibrium will be equal to 276 K.

Example 2

Figure 2 shows a section of the isotherm that corresponds to the transition of a substance from a crystalline to a liquid state. What corresponds to this site on the p, T diagram?

Drawing 2

Answer: The entire set of states that are depicted on the p, V diagram by a horizontal line segment on the p, T diagram is shown by one point, which determines the values ​​of p and T at which the transformation from one state of aggregation to another occurs.

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Literature

1. Korovin N.V. general chemistry... - M .: Higher. shk. - 1990, 560 p.

2. Glinka N.L. General chemistry. - M .: Higher. shk. - 1983, 650 p.

Ugai Ya.A. General and inorganic chemistry... - M .: Higher. shk. - 1997, 550

Lecture 3-5 (6 h)

Topic 3. Physical state of matter

The purpose of the lecture: to consider the general characteristics of the state of aggregation of matter; to analyze in detail the gaseous state of matter, the laws of ideal gases (the equation of state of an ideal gas, the laws of Boyle-Mariotte, Gay-Lussac, Charles, Avogadro, Dalton); real gases, van der Waals equation; give a characterization of the liquid and solid state of the substance; types of crystal lattices: molecular, atomic-covalent, ionic, metallic and mixed type.

Issues under study:

3.1. general characteristics aggregate state of matter.

3.2. The gaseous state of matter. The laws of ideal gases. Real gases.

3.3. Characteristics of the liquid state of matter.

3.4. Solid state characteristic.

3.5. Types of crystal lattices.

Almost all known substances depending on conditions, they are in a gaseous, liquid, solid or plasma state. This is called state of aggregation ... The state of aggregation does not affect Chemical properties and the chemical structure of a substance, but affects the physical state (density, viscosity, temperature, etc.) and the rate of chemical processes. For example, water in a gaseous state is vapor, in a liquid state - a liquid, in a solid state - ice, snow, frost. Chemical composition the same, but the physical properties are different. The difference in physical properties is associated with different distances between the molecules of the substance and the forces of attraction between them.

Gases are characterized by long distances between molecules and small forces of attraction. Gas molecules are in chaotic motion. This explains the fact that the density of gases is low, they do not have their own shape, they occupy the entire volume provided to them, when the pressure changes, the gases change their volume.

In liquid state the molecules are closer together, the forces of intermolecular attraction increase, the molecules are in a chaotic translational motion. Therefore, the density of liquids is much higher than the density of gases, the volume is determined, almost does not depend on pressure, but the liquids do not have their own form, but take the form of the provided vessel. They are characterized by "short-range order", that is, the rudiments of a crystalline structure (to be discussed below).

In solids particles (molecules, atoms, ions) are so close to each other that the forces of attraction are balanced by the forces of repulsion, that is, the particles have oscillatory movements, and there are no translational ones. Therefore, the particles of solids are located at certain points in space, they are characterized by "long-range order" (to be discussed below), solids have a definite shape, volume.

Plasma Is any object in which electrically charged particles (electrons, nuclei or ions) move chaotically. The plasma state in nature is dominant and arises under the influence of ionizing factors: high temperature, electric discharge, high-energy electromagnetic radiation, etc. There are two types of plasma: isothermal and gas discharge . The first arises under the influence of high temperature, is quite stable, exists for a long time, for example, the sun, stars, ball lightning... The second arises under the action of an electric discharge and is stable only in the presence of an electric field, for example, in gas-lighting tubes. Plasma can be thought of as an ionized gas that obeys the laws of an ideal gas.