Introduction
1. Aggregate state of matter - gas
2. Aggregate state of matter - liquid
3. Aggregate state of matter - solid
4. The fourth state of matter is plasma
Conclusion
List of used literature
Introduction
As you know, many substances in nature can be in three states: solid, liquid and gaseous.
The interaction of particles of matter in the solid state is most pronounced. The distance between molecules is approximately equal to their own sizes. This leads to a sufficiently strong interaction, which practically deprives the particles of the opportunity to move: they oscillate around a certain equilibrium position. They retain their shape and volume.
The properties of liquids are also explained by their structure. Particles of matter in liquids interact less intensively than in solids, and therefore they can change their location in leaps and bounds - liquids do not retain their shape - they are fluid.
A gas is a collection of molecules moving randomly in all directions independently of each other. Gases do not have their own shape, they occupy the entire volume provided to them and are easily compressed.
There is another state of matter - plasma.
The purpose of this work is to consider the existing aggregate states of matter, to identify all their advantages and disadvantages.
To do this, it is necessary to perform and consider the following aggregate states:
2. fluids
3. solids
3. Aggregate state of matter - solid
Solid, one of the four states of aggregation of matter, which differs from other states of aggregation (liquids, gases, plasmas) the stability of the form and the nature of the thermal motion of atoms that make small vibrations around the equilibrium positions. Along with the crystalline state of T. t., there is an amorphous state, including the glassy state. Crystals are characterized by long-range order in the arrangement of atoms. There is no long-range order in amorphous bodies.
Any substance is made up of molecules, and its physical properties depends on how the molecules are ordered and how they interact with each other. IN 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 (steam) states.
Gas expands until it fills the entire volume allotted to it. If we consider the gas molecular level, we will see molecules randomly rushing and colliding with each other and with the walls of the vessel, which, however, practically do not interact with each other. If you increase or decrease the volume of the vessel, the molecules will evenly redistribute in the new volume.
Unlike gas at a given temperature, it occupies a fixed volume, however, it also takes the form of a filled vessel - but only below its surface level. At the molecular level, the easiest way to think of a liquid is as spherical molecules that, although they are in close contact with each other, have the freedom to roll around each other, like round beads in a jar. Pour a liquid into a vessel - and the molecules will quickly spread and fill the lower part of the volume of the vessel, as a result, the liquid will take its shape, but will not spread in the full volume of the vessel.
Solid has its own shape, does not spread over the volume of the container
and does not take its form. At the microscopic level, atoms stick to each other chemical bonds, and their position relative to each other is fixed. At the same time, they can form as rigid ordered structures - crystal lattices, - and disorderly heap - amorphous bodies(This is exactly the structure of polymers, which look like mixed and sticky pasta in a bowl).
Three classical aggregate states of matter have been described above. There is, however, a fourth state, which physicists tend to classify as aggregate. This is the 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 water bodies evaporates and clouds form. So the liquid turns into a gas. In winter, the water in the reservoirs freezes, turning into a solid state, and in the spring it melts again, turning back into a liquid. What happens to the molecules of a substance when it changes from one state to another? Are they changing? Are, for example, 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. As it cools further, the water freezes, becoming solid, and the energy of the molecules is no longer enough even for free movement inside the body. They oscillate about one place, held by the attractive forces of other molecules.
In everyday practice, one has to deal not separately with individual atoms, molecules and ions, but with real substances - an aggregate a large number particles. Depending on the nature of their interaction, four types of aggregate state are distinguished: solid, liquid, gaseous and plasma. A substance can transform from one state of aggregation to another as a result of a corresponding phase transition.
The presence of a substance in a particular state of aggregation is due to the forces acting between the particles, the distance between them and the features of their movement. Each state of aggregation is characterized by a set of certain properties.
Properties of substances depending on the state of aggregation:
| state | property |
| gaseous |
|
| liquid |
|
| solid |
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In accordance with the degree of order in the system, each state of aggregation is characterized by its own ratio between the kinetic and potential energies of the particles. In solids, the potential predominates over the kinetic, since the particles occupy certain positions and only oscillate around them. For gases, there is an inverse relationship between potential and kinetic energies, as a consequence of the fact that gas molecules always move randomly, and there are almost no cohesive forces between them, so the gas occupies the entire volume. In the case of liquids, the kinetic and potential energies of the particles are approximately the same, a non-rigid bond acts between the particles, therefore fluidity and a constant volume are inherent in liquids.
When the particles of a substance form a regular geometric structure, and the energy of bonds between them is greater than the energy of thermal vibrations, which prevents the destruction of the existing structure, it means that the substance is in a solid state. But starting from a certain temperature, the energy of thermal vibrations exceeds the energy of bonds between particles. In this case, the particles, although they remain in contact, move relative to each other. As a result, the geometric structure is broken and the substance passes into a liquid state. If the thermal fluctuations increase so much that the connection between the particles is practically lost, the substance acquires a gaseous state. In an "ideal" gas, particles move freely in all directions.
When the temperature rises, the substance passes from an ordered state (solid) to a disordered state (gaseous); the liquid state is intermediate in terms of the ordering of particles.
The fourth state of aggregation is called plasma - a gas consisting of a mixture of neutral and ionized particles and electrons. Plasma is formed at ultrahigh temperatures (10 5 -10 7 0 C) due to the significant collision energy of particles that have the maximum disorder of motion. A mandatory feature of plasma, as well as other states of matter, is its electrical neutrality. But as a result of the disordered motion of particles in the plasma, separate charged microzones can appear, due to which it becomes a source of electromagnetic radiation. In the plasma state, there is matter on, stars, other space objects, as well as in thermonuclear processes.
Each state of aggregation is determined, first of all, by the range of temperatures and pressures, therefore, for a visual quantitative characteristic, a phase diagram of a substance is used, which shows the dependence of the state of aggregation on pressure and temperature.
Diagram of the state of matter with phase transition curves: 1 - melting-crystallization, 2 - boiling-condensation, 3 - sublimation-desublimation
The state diagram consists of three main areas, which correspond to the crystalline, liquid and gaseous states. Individual regions are separated by curves reflecting phase transitions:
- solid to liquid and vice versa, liquid to solid (melting-crystallization curve - dotted green graph)
- liquid to gaseous and reverse conversion of gas to liquid (boiling-condensation curve - blue graph)
- solid to gaseous and gaseous to solid (sublimation-desublimation curve - red graph).
The coordinates of the intersection of these curves are called the triple point, at which, under conditions of a certain pressure P \u003d P in and a certain temperature T \u003d T in, a substance can coexist in three states of aggregation at once, and the liquid and solid states have the same vapor pressure. The coordinates Pv and Tv are the only values of pressure and temperature at which all three phases can coexist simultaneously.
The point K on the phase diagram of the state corresponds to the temperature Tk - the so-called critical temperature, at which the kinetic energy of the particles exceeds the energy of their interaction and therefore the line of separation between the liquid and gas phases is erased, and the substance exists in the gaseous state at any pressure.
It follows from the analysis of the phase diagram that at a high pressure greater than at the triple point (P c), the heating of a solid ends with its melting, for example, at P 1, melting occurs at the point d. A further increase in temperature from T d to T e leads to the boiling of the substance at a given pressure P 1 . At a pressure Р 2 less than the pressure at the triple point Р в, heating the substance leads to its transition directly from the crystalline to the gaseous state (point q), that is, to sublimation. For most substances, the pressure at the triple point is lower than the saturation vapor pressure (P in
P saturated steam, therefore, when the crystals of such substances are heated, they do not melt, but evaporate, that is, they undergo sublimation. For example, iodine crystals or "dry ice" (solid CO 2) behave this way.
State Diagram Analysis gaseous state
Under normal conditions (273 K, 101325 Pa), both simple substances, the molecules of which consist of one (He, Ne, Ar) or several simple atoms (H 2, N 2, O 2), and complex substances with a low molar mass (CH 4, HCl, C 2 H 6).
Since the kinetic energy of gas particles exceeds their potential energy, the molecules in the gaseous state are constantly moving randomly. Due to the large distances between the particles, the forces of intermolecular interaction in gases are so small that they are not enough to attract particles to each other and keep them together. It is for this reason that gases do not have their own shape and are characterized by low density and high ability to compress and expand. Therefore, the gas constantly presses on the walls of the vessel in which it is located, equally in all directions.
To study the relationship between the most important gas parameters (pressure P, temperature T, amount of substance n, molar mass M, mass m), the simplest model of the gaseous state of matter is used - ideal gas, which is based on the following assumptions:
- the interaction between gas particles can be neglected;
- the particles themselves are material points that do not have their own size.
The most general equation describing the ideal gas model is considered to be the equations Mendeleev-Clapeyron for one mole of a substance:
However, the behavior of a real gas differs, as a rule, from the ideal one. This is explained, firstly, by the fact that between the molecules of a real gas there are still insignificant forces of mutual attraction that compress the gas to a certain extent. With this in mind, the total gas pressure increases by the value a/v2, which takes into account the additional internal pressure due to the mutual attraction of molecules. As a result, the total gas pressure is expressed by the sum P+ A/v2. Secondly, the molecules of a real gas have, albeit a small, but quite definite volume b , so the actual volume of all gas in space is V- b . When substituting the considered values into the Mendeleev-Clapeyron equation, we obtain the equation of state of a real gas, which is called van der Waals equation:
Where A And b are empirical coefficients that are determined in practice for each real gas. It is established that the coefficient a has a large value for gases that are easily liquefied (for example, CO 2, NH 3), and the coefficient b - on the contrary, the higher in size, the larger the gas molecules (for example, gaseous hydrocarbons).
The van der Waals equation describes the behavior of a real gas much more accurately than the Mendeleev-Clapeyron equation, which, nevertheless, is widely used in practical calculations due to its clear physical meaning. Although the ideal state of a gas is a limiting, imaginary case, the simplicity of the laws that correspond to it, the possibility of their application to describe the properties of many gases at low pressures and high temperatures, makes the ideal gas model very convenient.
Liquid state of matter
The liquid state of any particular substance is thermodynamically stable in a certain range of temperatures and pressures characteristic of the nature (composition) of the substance. The upper temperature limit of the liquid state is the boiling point above which a substance under conditions of stable pressure is in a gaseous state. The lower limit of the stable state of the existence of a liquid is the temperature of crystallization (solidification). Boiling and crystallization temperatures measured at a pressure of 101.3 kPa are called normal.
For ordinary liquids, isotropy is inherent - the uniformity of physical properties in all directions within the substance. Sometimes other terms are also used for isotropy: invariance, symmetry with respect to the choice of direction.
In the formation of views on the nature of the liquid state, the concept of the critical state, which was discovered by Mendeleev (1860), is of great importance:
A critical state is an equilibrium state in which the separation limit between a liquid and its vapor disappears, since the liquid and its saturated vapor acquire the same physical properties.
In the critical state, the values of both densities and specific volumes of the liquid and its saturated vapor become the same.
The liquid state of matter is intermediate between gaseous and solid. Some properties bring the liquid state closer to the solid. If solid substances are characterized by a rigid ordering of particles, which extends over a distance of hundreds of thousands of interatomic or intermolecular radii, then in the liquid state, as a rule, no more than a few tens of ordered particles are observed. This is explained by the fact that orderliness between particles in different places of a liquid substance quickly arises, and is just as quickly “blurred” again by thermal vibrations of particles. At the same time, the overall density of the “packing” of particles differs little from that of a solid, so the density of liquids does not differ much from the density of most solids. In addition, the ability of liquids to compress is almost as small as in solids (about 20,000 times less than that of gases).
Structural analysis confirmed that the so-called short range order, which means that the number of nearest "neighbors" of each molecule and their mutual arrangement are approximately the same throughout the volume.
A relatively small number of particles of different composition, connected by forces of intermolecular interaction, is called cluster . If all particles in a liquid are the same, then such a cluster is called associate . It is in clusters and associates that short-range order is observed.
The degree of order in various liquids depends on temperature. At low temperatures slightly above the melting point, the degree of order in the placement of particles is very high. As the temperature rises, it decreases and, as the temperature rises, the properties of the liquid approach the properties of gases more and more, and when the critical temperature is reached, the difference between the liquid and gaseous states disappears.
The proximity of the liquid state to the solid state is confirmed by the values of the standard enthalpies of vaporization DH 0 of evaporation and melting DH 0 of melting. Recall that the value of DH 0 evaporation shows the amount of heat that is needed to convert 1 mole of liquid into vapor at 101.3 kPa; the same amount of heat is spent on the condensation of 1 mole of vapor into a liquid under the same conditions (i.e. DH 0 evaporation = DH 0 condensation). The amount of heat required to convert 1 mole of a solid to a liquid at 101.3 kPa is called standard enthalpy of fusion; the same amount of heat is released during the crystallization of 1 mole of liquid under normal pressure conditions (DH 0 melting = DH 0 crystallization). It is known that DH 0 evaporation<< DН 0 плавления, поскольку переход из твердого состояния в жидкое сопровождается меньшим нарушением межмолекулярного притяжения, чем переход из жидкого в газообразное состояние.
However, other important properties of liquids are more like those of gases. So, like gases, liquids can flow - this property is called fluidity . They can resist the flow, that is, they are inherent viscosity . These properties are influenced by attractive forces between molecules, the molecular weight of the liquid substance, and other factors. The viscosity of liquids is about 100 times greater than that of gases. Just like gases, liquids can diffuse, but at a much slower rate because liquid particles are packed more densely than gas particles.
One of the most interesting properties of the liquid state, which is not characteristic of either gases or solids, is surface tension .
Diagram of the surface tension of a liquid A molecule located in a liquid volume is uniformly acted upon by intermolecular forces from all sides. However, on the surface of the liquid, the balance of these forces is disturbed, as a result of which the surface molecules are under the action of some resultant force, which is directed inside the liquid. For this reason, the liquid surface is in a state of tension. Surface tension is the minimum force that keeps the particles of a liquid inside and thereby prevents the surface of the liquid from contracting.
Structure and properties of solids
Most of the known substances, both natural and artificial, are in the solid state under normal conditions. Of all the compounds known today, about 95% are solids, which have become important, since they are the basis of not only structural, but also functional materials.
- Structural materials are solids or their compositions that are used to make tools, household items, and various other structures.
- Functional materials are solids, the use of which is due to the presence of certain useful properties in them.
For example, steel, aluminum, concrete, ceramics belong to structural materials, and semiconductors, phosphors belong to functional ones.
In the solid state, the distances between the particles of matter are small and have the same order of magnitude as the particles themselves. The interaction energies between them are large enough, which prevents the free movement of particles - they can only oscillate about certain equilibrium positions, for example, around the nodes of the crystal lattice. The inability of particles to move freely leads to one of the most characteristic features of solids - the presence of their own shape and volume. The ability to compress solids is very small, and the density is high and little dependent on temperature changes. All processes occurring in solid matter occur slowly. The laws of stoichiometry for solids have a different and, as a rule, broader meaning than for gaseous and liquid substances.
The detailed description of solids is too voluminous for this material and is therefore covered in separate articles:, and.
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. At sufficiently 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, pass into a solid body, 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(rectangular parallelepiped),
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 various directions within 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 a covalent bond, ionic - in ionic compounds, metallic - in 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 inorganic 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 as follows:
- 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 is obtained at a high rate of 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 the cooling of the earth's crust or deep layers of volcanoes, has a coarse-grained structure, in contrast to volcanic glass, which has frozen on the surface and is 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 the application of structural analysis methods to liquids, it was 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.
Definition 1
Aggregate states of matter(from the Latin “aggrego” means “I attach”, “I bind”) - these are the states of the same substance in solid, liquid and gaseous form.
During the transition from one state to another, an abrupt change in energy, entropy, density and other properties of matter is observed.
Solid and liquid bodies
Definition 2Solids- 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 the kinetic energy.
Solid bodies are divided into 2 types:
- crystalline;
- Amorphous.
Only crystalline bodies are in a state of thermodynamic equilibrium. Amorphous bodies, in fact, are metastable states, which are similar in structure to non-equilibrium, slowly crystallizing liquids. In an amorphous body, an excessively slow process of crystallization takes place, a process of gradual transformation of a substance into a crystalline phase. The difference between a crystal and an amorphous solid lies primarily 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 body 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 crystal atoms creates the so-called crystal lattice. In different directions, the location of atoms in the lattice is different, which leads to anisotropy. Atoms (ions or whole molecules) in the crystal lattice perform random oscillatory motion near the middle positions, which are considered as nodes of the crystal lattice. The higher the temperature, the higher the energy of oscillations, and hence the average amplitude of oscillations. Depending on the amplitude of oscillations, the size of the crystal is determined. An increase in the amplitude of oscillations leads to an increase in the size of the body. Thus, the thermal expansion of solids is explained.
Definition 3
liquid bodies- These are bodies that have a certain volume, but do not have an elastic shape.
A substance in the liquid state is characterized by strong intermolecular interaction and low compressibility. A liquid occupies an intermediate position between a solid and a gas. Liquids, like gases, have isotopic properties. In addition, the liquid has the property of fluidity. In it, as in gases, there is no shear stress (shear stress) bodies. Liquids are heavy, that is, their specific gravity can be compared with the specific gravity of solids. Near the crystallization temperatures, their heat capacities and other thermal properties are close to those of solids. In liquids, the correct arrangement of atoms is observed to a given extent, but only in small areas. Here, the atoms also perform an oscillatory motion around the nodes of the quasicrystalline cell, but, unlike the atoms of a solid body, they periodically jump from one node to another. As a result, the movement of atoms will be very complex: oscillatory, but at the same time, the center of oscillations moves in space.
Definition 4Gas This is a state of matter in which the distances between molecules are huge.
The forces of interaction between molecules at low pressures can be neglected. Gas particles fill the entire volume that is provided for gas. Gases are considered as highly superheated or unsaturated vapors. A special type of gas is plasma (a partially or fully ionized gas in which the densities of positive and negative charges are almost the same). That is, a plasma is a gas of charged particles interacting with each other using electrical forces at a great distance, but not having near and far particles.
As you know, substances are able to move from one state of aggregation to another.
Definition 5
Evaporation- this is the 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 converts the potential energy of the interaction of molecules.
Evaporation is a phase transition. During evaporation, part of the liquid or solid is converted into 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 mass of the body, r is the specific heat of vaporization (J / k g).
Definition 7
Condensation is the reverse process of vaporization.
The change in internal energy is calculated by formula (1) .
Definition 8
Melting- This is the process of converting a substance from a solid state to a liquid state, the process of changing the state of aggregation of a substance.
When a substance is heated, its internal energy increases, therefore, the speed of thermal movement of molecules increases. When a substance reaches its melting point, the crystal lattice of a solid is destroyed. Bonds between particles are also destroyed, and the energy of interaction between particles increases. The heat that is transferred to the body goes to increase the internal energy of this body, and part of the energy is spent on doing work to change the volume of the body when it melts. For many crystalline bodies, the volume increases when melted, but there are exceptions (for example, ice, cast iron). Amorphous bodies do not have a specific melting point. Melting is a phase transition, which is characterized by an abrupt change in heat capacity at the melting temperature. The melting point depends on the substance and remains constant 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 f / k g) .
Definition 9
Crystallization is the reverse process of melting.
The change in internal energy is calculated by 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, J to g K, △ T is the change in body temperature.
Definition 10
When considering the transformations of substances from one state of aggregation to another, one cannot do without the so-called heat balance equations: the total amount of heat released in a thermally 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 essence, the heat balance equation is the energy conservation law for heat transfer processes in thermally insulated systems.
Example 1
In a heat-insulated vessel are water and ice with a temperature t i = 0 ° C. The mass of water m υ and ice m i is respectively equal to 0.5 kg and 60 g. Water vapor of mass m p = 10 g is let into the water at a temperature 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 which processes are carried out in the system, which aggregate states of matter we observed and which ones we obtained.
Water vapor condenses, giving off heat.
Thermal energy is spent on melting ice and, perhaps, heating the water available and obtained from ice.
First of all, let's check how much heat is released during the condensation of the available mass of steam:
Q p = - r m p ; Q p \u003d 2, 26 10 6 10 - 2 \u003d 2, 26 10 4 (D w),
here from reference materials we have r = 2.26 10 6 J k g - the specific heat of vaporization (it is also used for condensation).
To melt ice, you need the following amount of heat:
Q i \u003d λ m i Q i \u003d 6 10 - 2 3, 3 10 5 ≈ 2 10 4 (D w),
here, from reference materials, we have λ = 3, 3 10 5 J k g - the specific heat of ice melting.
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 condensation of steam of mass m p and cooling of water formed from steam from temperature T p to the desired T . Heat is absorbed when ice with mass m i melts and water with mass m υ + m i is heated from temperature T i to T . Denote T - T i = ∆ T for the difference T p - T we get:
T p - T = T p - T i - ∆ T = 100 - ∆ T .
The heat balance equation will look like:
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 \u003d 4, 2 10 3 J k g K, T p \u003d t p + 273 \u003d 373 K, T i \u003d t i + 273 \u003d 273 K: ∆ T \u003d 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 276 K.
Example 2
Figure 2 shows a section of the isotherm, which corresponds to the transition of a substance from a crystalline to a liquid state. What corresponds to this section on the p, T diagram?
Drawing 2
Answer: The entire set of states that are shown on the p , V diagram as 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 takes place.
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