The transformation of a liquid into a solid is called. Change in the state of aggregation of matter. Evaporation - vaporization that occurs from the surface

In this section, we will look at aggregate states, in which the matter around us resides and the forces of interaction between the particles of matter, characteristic of each of the aggregate states.

1. Solid State,

2. liquid state And

3. gaseous state.

Often a fourth state of aggregation is distinguished - plasma.

Sometimes, the plasma state is considered one of the types of gaseous state.

Plasma - partially or fully ionized gas, most often present at high temperatures.

Plasma is the most common state of matter in the universe, since the matter of stars is in this state.

For each state of aggregation characteristic features in the nature of the interaction between the particles of a substance, which affects its physical and chemical properties.

Each substance can be in different states of aggregation. When enough low temperatures all substances are in solid state. But as they heat up, they become liquids, then gases. Upon further heating, they ionize (the atoms lose some of their electrons) and pass into the state plasma.

Gas

gaseous state(from Dutch. gas, goes back to other Greek. Χάος ) characterized by very weak bonds between its constituent particles.

The molecules or atoms that form the gas move randomly and, at the same time, they are at large (in comparison with their sizes) distances from each other for the majority of the time. Consequently interaction forces between gas particles are negligible.

The main feature of the gas is that it fills all available space without forming a surface. Gases always mix. Gas is an isotropic substance, that is, its properties do not depend on direction.

In the absence of gravity pressure the same at all points in the gas. In the field of gravitational forces, density and pressure are not the same at each point, decreasing with height. Accordingly, in the field of gravity, the mixture of gases becomes inhomogeneous. heavy gases tend to settle lower and more lungs- to go up.

The gas has a high compressibility- when the pressure increases, its density increases. As the temperature rises, they expand.

When compressed, a gas can turn into a liquid., but condensation does not occur at any temperature, but at a temperature below the critical temperature. The critical temperature is a characteristic of a particular gas and depends on the forces of interaction between its molecules. So, for example, gas helium can only be liquefied at temperatures below 4.2K.

There are gases that, when cooled, turn into solid bypassing the liquid phase. The transformation of a liquid into a gas is called evaporation, and the direct transformation of a solid into a gas is called sublimation.

Solid

Solid State in comparison with other states of aggregation characterized by shape stability.

Distinguish crystalline And amorphous solids.

Crystalline state of matter

The stability of the shape of solids is due to the fact that most of the solids have crystalline structure.

In this case, the distances between the particles of the substance are small, and the interaction forces between them are large, which determines the stability of the form.

It is easy to verify the crystalline structure of many solids by splitting a piece of matter and examining the resulting fracture. Usually, at a break (for example, in sugar, sulfur, metals, etc.), small crystal faces located at different angles are clearly visible, gleaming due to the different reflection of light by them.

In cases where the crystals are very small, the crystal structure of the substance can be established using a microscope.

Crystal forms

Each substance forms crystals perfectly defined form.

The variety of crystalline forms can be summarized in seven groups:

1. Triclinic(parallelepiped),

2.Monoclinic(prism with a parallelogram at the base),

3. Rhombic (cuboid),

4. tetragonal(rectangular parallelepiped with a square at the base),

5. Trigonal,

6. Hexagonal(prism with the base of the right centered
hexagon),

7. cubic(cube).

Many substances, in particular iron, copper, diamond, sodium chloride, crystallize in cubic system. The simplest forms of this system are cube, octahedron, tetrahedron.

Magnesium, zinc, ice, quartz crystallize in hexagonal system. The main forms of this system are hexagonal prisms and bipyramid.

Natural crystals, as well as crystals obtained artificially, rarely correspond exactly to theoretical forms. Usually, when the molten substance solidifies, the crystals grow together and therefore the shape of each of them is not quite correct.

However, no matter how unevenly the crystal develops, no matter how distorted its shape, the angles at which the crystal faces converge in the same substance remain constant.

Anisotropy

Features of crystalline bodies are not limited to the shape of crystals. Although the substance in a crystal is perfectly homogeneous, many of its physical properties- strength, thermal conductivity, relation to light, etc. - are not always the same in different directions inside the crystal. This important feature of crystalline substances is called anisotropy.

Internal structure of crystals. Crystal lattices.

The external shape of a crystal reflects its internal structure and is due to the correct arrangement of the particles that make up the crystal - molecules, atoms or ions.

This arrangement can be represented as crystal lattice- a spatial frame formed by intersecting straight lines. At the points of intersection of the lines - lattice nodes are the centers of the particles.

Depending on the nature of the particles located at the nodes of the crystal lattice, and on what forces of interaction between them prevail in a given crystal, the following types are distinguished crystal lattices:

1. molecular,

2. atomic,

3. ionic And

4. metal.

Molecular and atomic lattices are inherent in substances with covalent bond, ionic - to ionic compounds, metallic - to metals and their alloys.

At the nodes of atomic lattices are atoms. They are connected to each other covalent bond.

There are relatively few substances that have atomic lattices. They belong to diamond, silicon and some don't organic compounds.

These substances are characterized by high hardness, they are refractory and practically insoluble in any solvents. These properties are due to their durability. covalent bond.

Molecules are located at the nodes of molecular lattices. They are connected to each other intermolecular forces.

There are a lot of substances with a molecular lattice. They belong to nonmetals, with the exception of carbon and silicon, all organic compounds with non-ionic bond and many inorganic compounds.

The forces of intermolecular interaction are much weaker than the forces of covalent bonds, therefore molecular crystals have low hardness, fusible and volatile.

In the nodes of ionic lattices, positively and negatively charged ions are located, alternating. They are connected to each other by forces electrostatic attraction.

Ionic compounds that form ionic lattices include most salts and a small number of oxides.

By strength ionic lattices inferior to atomic, but exceed molecular.

Ionic compounds have relatively high melting points. Their volatility in most cases is not great.

At the nodes of metal lattices there are metal atoms, between which electrons common to these atoms move freely.

The presence of free electrons in the crystal lattices of metals can explain many of their properties: plasticity, malleability, metallic luster, high electrical and thermal conductivity.

There are substances in whose crystals two kinds of interactions between particles play a significant role. So, in graphite, carbon atoms are connected to each other in the same directions. covalent bond, and in others metallic. Therefore, the graphite lattice can also be considered as nuclear, And How metal.

In many inorganic compounds, for example, in BeO, ZnS, CuCl, the connection between the particles located at the lattice sites is partially ionic, and partly covalent. Therefore, lattices of such compounds can be considered as intermediate between ionic And atomic.

Amorphous state of matter

Properties of amorphous substances

Among solid bodies there are those in which no signs of crystals can be found in the fracture. For example, if you break a piece of ordinary glass, then its break will be smooth and, unlike the breaks of crystals, it is limited not by flat, but by oval surfaces.

A similar picture is observed when splitting pieces of resin, glue and some other substances. This state of matter is called amorphous.

Difference between crystalline And amorphous bodies is particularly pronounced in their relation to heating.

While the crystals of each substance melt at a strictly defined temperature and at the same temperature a transition from a liquid state to a solid occurs, amorphous bodies do not have a constant melting point. When heated, the amorphous body gradually softens, begins to spread and, finally, becomes completely liquid. When cooled, it also gradually hardens.

Due to the lack of a specific melting point, amorphous bodies have a different ability: many of them flow like liquids, i.e. with prolonged action of relatively small forces, they gradually change their shape. For example, a piece of resin placed on a flat surface spreads in a warm room for several weeks, taking the form of a disk.

The structure of amorphous substances

Difference between crystalline and amorphous state of matter is as follows.

Ordered arrangement of particles in a crystal, reflected by the unit cell, is preserved in large areas of crystals, and in the case of well-formed crystals - in their entirety.

In amorphous bodies, order in the arrangement of particles is observed only in very small areas. Moreover, in a number of amorphous bodies even this local ordering is only approximate.

This difference can be summarized briefly in the following way:

• crystal structure is characterized by long-range order,
• structure of amorphous bodies - near.

Examples of amorphous substances.

Stable amorphous substances include glass(artificial and volcanic), natural and artificial resins, glues, paraffin, wax and etc.

Transition from an amorphous state to a crystalline one.

Some substances can be in both crystalline and amorphous states. Silicon dioxide SiO 2 occurs in nature in the form of well-formed quartz crystals, as well as in the amorphous state ( flint mineral).

Wherein the crystalline state is always more stable. Therefore, a spontaneous transition from a crystalline to an amorphous substance is impossible, and the reverse transformation - a spontaneous transition from an amorphous state to a crystalline one - is possible and sometimes observed.

An example of such a transformation is devitrification- spontaneous crystallization of glass at elevated temperatures, accompanied by its destruction.

amorphous state many substances are obtained with high speed solidification (cooling) of the liquid melt.

For metals and alloys amorphous state is formed, as a rule, if the melt is cooled for a time on the order of fractions or tens of milliseconds. For glasses, a much lower cooling rate is sufficient.

Quartz (SiO2) also has a low crystallization rate. Therefore, the products cast from it are amorphous. However, natural quartz, which had hundreds and thousands of years to crystallize during cooling earth's crust or deep layers of volcanoes, has a macrocrystalline structure, in contrast to volcanic glass, which is frozen on the surface and therefore amorphous.

Liquids

Liquid is an intermediate state between a solid and a gas.

liquid state is intermediate between gaseous and crystalline. According to some properties, liquids are close to gases, according to others - to solid bodies.

With gases, liquids are brought together, first of all, by their isotropy And fluidity. The latter determines the ability of the liquid to easily change its shape.

However high density And low compressibility liquids brings them closer to solid bodies.

The ability of liquids to easily change their shape indicates the absence of hard forces of intermolecular interaction in them.

At the same time, the low compressibility of liquids, which determines the ability to maintain a constant volume at a given temperature, indicates the presence, although not rigid, but still significant forces of interaction between particles.

The ratio of potential and kinetic energy.

Each state of aggregation is characterized by its own ratio between the potential and kinetic energies of the particles of matter.

In solids, the average potential energy of particles is greater than their average kinetic energy. Therefore, in solids, particles occupy certain positions relative to each other and only oscillate relative to these positions.

For gases, the energy ratio is reversed, as a result of which the gas molecules are always in a state of chaotic motion and there are practically no cohesive forces between the molecules, so that the gas always occupies the entire volume provided to it.

In the case of liquids, the kinetic and potential energies of particles are approximately the same, i.e. particles are connected to each other, but not rigidly. Therefore, liquids are fluid, but have a constant volume at a given temperature.

The structures of liquids and amorphous bodies are similar.

As a result of applying methods to liquids structural analysis found that the structure liquids are like amorphous bodies. Most liquids have short range order- the number of nearest neighbors for each molecule and their mutual arrangement are approximately the same throughout the entire volume of the liquid.

The degree of ordering of particles in different liquids is different. In addition, it changes with temperature.

At low temperatures, slightly exceeding the melting point of a given substance, the degree of order in the arrangement of the particles of a given liquid is high.

As the temperature rises, it decreases and as the liquid heats up, the properties of the liquid more and more approach the properties of the gas. When the critical temperature is reached, the distinction between liquid and gas disappears.

Due to the similarity in the internal structure of liquids and amorphous bodies, the latter are often considered as liquids with a very high viscosity, and only substances in the crystalline state are classified as solids.

Likening amorphous bodies liquids, however, it should be remembered that in amorphous bodies, unlike ordinary liquids, particles have a slight mobility - the same as in crystals.

It is important to know and understand how transitions between aggregate states of substances are carried out. The scheme of such transitions is depicted in Figure 4.

5 - sublimation (sublimation) - transition from a solid state to a gaseous state, bypassing the liquid state;

6 - desublimation - transition from a gaseous state to a solid state, bypassing the liquid state.

B. 2 Melting of ice and freezing of water (crystallization)
If you put ice in a flask and start heating it with a burner, you will notice that its temperature will begin to rise until it reaches its melting point (0 o C). Then the melting process will begin, but the temperature of the ice will not increase, and only after the end of the melting process of all the ice, the temperature of the formed water will begin to rise.

Definition. Melting- the process of transition from a solid to a liquid state. This process takes place at a constant temperature.

The temperature at which a substance melts is called the melting point and is a measured value for many solids and is therefore a tabular value. For example, the melting point of ice is 0 o C, and the melting point of gold is 1100 o C.

The reverse process of melting - the process of crystallization - is also conveniently considered by the example of freezing water and turning it into ice. If you take a test tube with water and begin to cool it, then at first there will be a decrease in the temperature of the water until it reaches 0 o C, and then it will freeze at a constant temperature), and after complete freezing, further cooling of the formed ice.
If the described processes are considered from the point of view of the internal energy of the body, then during melting, all the energy received by the body is spent on the destruction of the crystal lattice and the weakening of intermolecular bonds, thus, the energy is spent not on changing the temperature, but on changing the structure of the substance and the interaction of its particles. In the process of crystallization, the energy exchange takes place in reverse direction: the body gives off heat environment, And his internal energy decreases, which leads to a decrease in the mobility of particles, an increase in the interaction between them and solidification of the body.

Melting and crystallization chart

It is useful to be able to graphically depict the processes of melting and crystallization of a substance on a graph. Along the axes of the graph are located: the abscissa axis - time, the ordinate axis - the temperature of the substance. As the substance under study, we will take ice at a negative temperature, i.e., one that, upon receiving heat, will not immediately begin to melt, but will be heated to the melting point. Let us describe the sections on the graph, which represent separate thermal processes:
Initial state - a: heating ice to a melting temperature of 0 o C;
a - b: melting process at a constant temperature of 0 o C;
b - point with a certain temperature: heating the water formed from ice to a certain temperature;
Point with a certain temperature - c: cooling water to freezing point 0 o C;
c - d: the process of freezing water at a constant temperature of 0 o C;
d - final state: ice cooling down to some negative temperature.

Back forward

Attention! The slide preview is for informational purposes only and may not represent the full extent of the presentation. If you are interested in this work, please download the full version.

Goals: formation of the concept of melting and crystallization of bodies, the temperature of melting and crystallization; the development of skills to apply the knowledge gained to solving the simplest problems, the development of the horizons of students, the education of interest in the subject, the education of a comprehensively developed personality.

Necessary equipment: Teacher's workstation, physics lessons of Cyril and Methodius for grade 8, pieces of ice, candle, matches.

Explanations: Student responses are in italics in the text.

Lesson plan:

1. Organizing time.
2. Learning new material.
3. Consolidation.
4. Homework.
5. Lesson results.

DURING THE CLASSES

1. Organizational moment

- Today in the lesson we will talk about the different states of matter, find out under what conditions a substance can be in one state or another and what needs to be done to transform a substance from one state to another.

2. Learning new material

- Consider the pictures (slide 2). What do you think they have in common?

– The figures show water in three different states: solid, liquid and gaseous.

- Right. Not only water, but also any other substance has three states. What are these states called?

–

Can matter change from one state to another? For example, can you turn ice into water?

– Yes.

– How to do it?

– You need to heat it up.

– You are almost right. It would be more correct to say that we impart a certain amount of heat to the ice. Then what is the amount of heat?

– The amount of heat is the energy that the body receives or gives off in the process of heat transfer.

What is internal energy?

– Internal energy is the energy of movement and interaction of particles that make up the body.

- Let's do an experiment. Let's leave one piece of ice on a plate and see what will happen to it, and to the second we will transfer a certain amount of heat from the candle. Which piece of ice turns into water faster and why?

– In the second case, the process of transition of ice into water is faster, since the second piece of ice receives more heat from the candle than the first piece from the environment.

- Right. This means that the piece of ice to which more energy is given turns into water faster.

- Find in the textbook (p. 31), what is the name of the process of transition of a substance from a solid to a liquid state?

Process the transition of a substance from a solid to a liquid state is called melting (slide 3)

This is the topic of our lesson. Let's write in a notebook - Melting bodies.

– Consider the process of melting with the help of a fragment (physics lessons of Cyril and Methodius for grade 8). Your task is to pay attention to whether the temperature changes during this process.

– The temperature during the melting process does not change.

- Right. Now find in the textbook (p. 32), what is the name of the process of transition of a substance from a liquid to a solid state?

The transition of a substance from a liquid to a solid state is called solidification, or crystallization. (slide 4)

- Let's consider this process with the help of a fragment (electronic physics lessons of Cyril and Methodius for grade 8). Did the temperature change during the entire curing process?

– The temperature during the curing process did not change.

- Remember that in the process of melting and solidification the temperature of the substance does not change. Why this happens, we will look at the next lesson.

- In order for the melting process to begin, the body must have a certain temperature. What is it called?

The temperature at which a substance melts is called its melting point.

- Right! This means that the melting point is the temperature above which a substance cannot exist in the solid state. Find the melting point of ice in the table of melting points.

– It is equal to 0 O WITH.

At what temperature does water solidify?

– Water also hardens at 0 O WITH.

- Right. This means that substances solidify at the same temperature at which they melt.
Using the graph (slide 5), we will consider the process of transition of ice from a solid state to a liquid state (Peryshkin A.V., p. 33).
The observation of the process began from the moment when the temperature of the ice was -20 o C. With further heating, the temperature of the ice increased until it reached 0 o C. At this moment, the ice began to melt, and its temperature stopped rising. During the entire time of melting, the temperature of the ice did not change, although energy was continued to be imparted to it.
When 20 o C was reached, energy was no longer imparted to the substance: the water began to cool, and at 0 o C, the process of water crystallization began. During the entire time of solidification, the temperature of the substance again did not change. It can also be seen from the graph that the melting temperature is equal to the crystallization temperature.

3. Fixing

1. The graph (slide 6) shows how the temperature changes over time when heating and cooling lead. What state does each section of the graph correspond to?

AB, BC - solid state, CD - melting,
DE, EF - liquid state, FG - crystallization, GH - solid state.

2. In the experiment, aluminum, iron, copper, zinc, steel, silver and gold were separately heated to 1000 o C (slide 7, 8). In what state - liquid or solid - were these metals at the specified temperature?

3. The figures (slide 2) show water in three different states: solid, liquid and gaseous.

What are these states called?

– They are called aggregate states.

Can matter change from one state to another?
Yes. By transferring energy to the molecules of a solid, it is possible to transfer a substance from a solid state to a liquid state, and from a liquid state to a gas. By taking away energy from gas molecules, you can get a liquid, and from it - a solid body.

4. - We begin to heat the ice taken at a temperature of -10 o C. What happens to the temperature?

– The temperature of the ice will increase.

– The temperature of the ice has reached 0 o C. The ice is starting to melt. What happens to its temperature?

– The temperature stops changing until the end of the entire melting process.

The ice has completely turned into water. The heating process continues. Does the temperature change? How?

– Is the water temperature already rising again?

5. Does the temperature of a substance change during crystallization?

1. Solid state
2. liquid state
3. gaseous state
4. Change in the state of matter

Chemistry is the study of matter. What is a "substance"? Matter is anything that has mass and volume. A substance can be in one of three aggregate states: solid, liquid, gaseous.

1. Solid State

Particles (molecules) in a solid body are combined into a rigid repeating structure - crystal lattice. Particles in the crystal lattice make small vibrations around the centers of equilibrium. The solid has form And volume.

2. Liquid state

Unlike solids, a liquid does not have a definite shape, but has a volume. This is explained by the fact that in liquids the particles are at a greater distance from each other than in solids and move more actively.

Since the particles in liquids are less dense than in solids, they cannot form a crystal lattice, therefore liquids do not have a definite shape.

3. Gaseous state

In a gas, particles are still at greater distances than in liquids. Moreover, the particles are constantly in chaotic (random) motion. Therefore, gases tend to uniformly fill the volume provided to them (hence the fact that gases do not have a definite shape).

4. Change in the state of matter

Let's take a banal example and follow the process of changing the state of water.

In its solid state, water is ice. The temperature of the ice is less than 0 ° C. When heated, the ice begins to melt and turn into water. This is due to the fact that ice particles in the crystal lattice begin to move when heated, as a result of which the lattice is destroyed. The temperature at which a substance melts is called "melting point" substances. The melting point of water is 0 o C.

It should be noted that until the ice is completely melted, the temperature of the ice will be 0 o C.

After the ice has completely turned into water, we will continue heating. The temperature of the water will rise, and the movement of particles under the influence of heat will be accelerated more and more. This happens until the water reaches its next state change point - boiling.

This moment comes when the bonds of water particles are completely broken and their movement becomes free: water turns into steam.

The temperature at which a liquid boils is called "boiling point".

Note that the boiling point depends on pressure. At normal pressure (760 mm Hg), the boiling point of water is 100 o C.

By analogy with melting: until the water completely turns into steam, the temperature will be constant.

Summarize. As a result of heating, we obtained different phase states of water:

Ice → water → steam or H 2 0 (t) → H 2 0 (g) → H 2 0 (g)

What happens if we start to cool the water vapor? You don't have to be "seven spans in the forehead" to guess - the reverse process of phase changes in water will go on:

Steam → water → ice

There are some substances that go directly from a solid state to a gaseous state, bypassing the liquid phase. Such a process is called sublimation or sublimation. So, for example, behaves "dry ice" (nitrogen dioxide CO 2). When it is heated, you will not see a drop of water - the "dry ice" will seem to evaporate before your eyes.

The process that is the reverse of sublimation (the transition of a substance from a gas to a solid state) is called desublimation.

Aggregate transformations of matter.

Three states of matter.

aggregate transformations.

melting and solidification process.

• The transition from a solid to a liquid state is called melting. The reverse is called hardening. If a crystalline solid is obtained during solidification of a liquid, then such solidification is called crystallization.

Melting and crystallization temperature.

• melting point A given substance is called the temperature at which the solid and liquid states of this substance coexist simultaneously. The melting temperature does not depend on the heating rate. Until the end of melting, the temperature of the body and the melt remains the same.

• The temperature at which a substance changes from a liquid to a solid state is called crystallization temperature.

TEMPERATURE GRAPH OF CHANGES IN AGGREGATE STATES OF WATER.

Calculation of the amount of heat during melting (crystallization)

Explanation of the melting process.

• The liquid state of matter, compared to the solid crystalline state, is characterized by:

• high speed of movement of molecules;

• greater distance between molecules;

• the absence of a strict arrangement of molecules.

• Therefore, for the transformation of a solid body into a liquid, additional energy must be imparted to its molecules.

• The liquid state corresponds to a large internal energy.

Vaporization The transition of a substance from a liquid state to a gaseous state

• Evaporation - vaporization that occurs from the surface

• liquids at any temperature

vaporization conditions.

• free surface area is the first factor affecting the rate of vaporization.

Boiling.

• Vaporization occurring throughout the entire volume of the liquid due to the emergence and ascent to the surface of numerous bubbles of saturated vapor is called boiling.

Boiling is happening with takeover warmth. Most of input heat is spent on breaking ties between the particles of matter, the rest - for the work done during the expansion of steam. As a result, the interaction energy between vapor particles becomes greater than between liquid particles, so the internal energy of the vapor is greater than the internal energy of the liquid at the same temperature.

Specific heat of vaporization.

• The amount of heat required to transfer liquid to vapor during the boiling process can be calculated by the formula:

• where m is the mass of liquid (kg), L is the specific heat of vaporization.

• Specific heat of vaporization shows how much heat is needed to turn 1 kg of a given substance into steam at the boiling point. Unit specific heat of vaporization in the SI system: [ L ] = 1 J/kg

Boiling temperature.

During the boil temperature liquids does not change.. Boiling temperature depends from the pressure exerted on the liquid. Every substance at the same pressure has my boiling temperature. With an increase atmospheric pressure boiling begins at a higher temperature, with a decrease in pressure - vice versa .. For example, water boils at 100 ° C only at normal atmospheric pressure.