How to determine the state of aggregation of matter. Aggregate states of matter
State of aggregation- a state of matter characterized by certain qualitative properties: the ability or inability to maintain volume and shape, the presence or absence of long-range and short-range order, and others. A change in the state of aggregation may be accompanied by a jump-like change in free energy, entropy, density, and other basic physical properties.
There are three main states of aggregation: solid, liquid and gas. Sometimes it is not entirely correct to classify plasma as a state of aggregation. There are other states of aggregation, for example, liquid crystals or Bose-Einstein condensate. Changes in the state of aggregation are thermodynamic processes called phase transitions. The following varieties are distinguished: from solid to liquid - melting; from liquid to gaseous - evaporation and boiling; from solid to gaseous - sublimation; from gaseous to liquid or solid - condensation; from liquid to solid - crystallization. A distinctive feature is the absence of a sharp boundary of the transition to the plasma state.
Aggregate state definitions are not always strict. So, there are amorphous bodies that retain the structure of a liquid and have little fluidity and the ability to retain shape; liquid crystals are fluid, but at the same time they have some properties of solids, in particular, they can polarize electromagnetic radiation passing through them. To describe various states in physics, a broader concept of a thermodynamic phase is used. Phenomena that describe transitions from one phase to another are called critical phenomena.
The aggregate state of a substance depends on the physical conditions in which it is located, mainly on temperature and pressure. The determining quantity is the ratio of the average potential energy of the interaction of molecules to their average kinetic energy. So, for a solid body this ratio is greater than 1, for gases it is less than 1, and for liquids it is approximately equal to 1. The transition from one state of aggregation of a substance to another is accompanied by an abrupt change in the value of this ratio, associated with an abrupt change in intermolecular distances and intermolecular interactions. In gases, the intermolecular distances are large, the molecules almost do not interact with each other and move almost freely, filling the entire volume. In liquids and solids - condensed media - molecules (atoms) are located much closer to each other and interact more strongly.
This leads to the preservation of liquids and solids of their volume. However, the nature of the movement of molecules in solids and liquids is different, which explains the difference in their structure and properties.
In solids in a crystalline state, atoms only vibrate near the nodes of the crystal lattice; the structure of these bodies is characterized by a high degree of order - long-range and short-range order. The thermal motion of molecules (atoms) of a liquid is a combination of small fluctuations around equilibrium positions and frequent jumps from one equilibrium position to another. The latter determine the existence in liquids of only short-range order in the arrangement of particles, as well as their inherent mobility and fluidity.
A. Solid- a state characterized by the ability to maintain volume and shape. Atoms of a solid body make only small vibrations around the state of equilibrium. There is both long-range and short-range order.
b. Liquid- a state of matter in which it has low compressibility, that is, it retains its volume well, but is not able to retain its shape. The liquid easily takes the shape of the vessel in which it is placed. Atoms or molecules of a liquid vibrate near the equilibrium state, locked by other atoms, and often jump to other free places. There is only short-range order.
Melting- this is the transition of a substance from a solid state of aggregation (see Aggregate states of matter) to a liquid. This process occurs during heating, when a certain amount of heat +Q is imparted to the body. For example, the low-melting metal lead passes from a solid state to a liquid state if it is heated to a temperature of 327 ° C. Lead easily melts on a gas stove, for example, in a stainless steel spoon (it is known that the flame temperature of a gas burner is 600-850 ° C, and the temperature melting of steel - 1300-1500°C).
If, while melting lead, its temperature is measured, then it can be found that at first it gradually increases, but after a certain moment it remains constant, despite further heating. This moment corresponds to melting. The temperature is held constant until all the lead has melted, and only then does it begin to rise again. When liquid lead is cooled, the opposite is observed: the temperature drops until solidification begins and remains constant all the time until the lead passes into the solid phase, and then decreases again.
All pure substances behave in the same way. The constancy of temperature during melting is of great practical importance, since it allows calibrating thermometers, making fuses and indicators that melt at a strictly specified temperature.
Atoms in a crystal vibrate about their equilibrium positions. As the temperature rises, the oscillation amplitude increases and reaches a certain critical value, after which the crystal lattice is destroyed. This requires additional thermal energy, so during the melting process the temperature does not rise, although heat continues to flow.
The melting point of a substance depends on pressure. For substances whose volume increases during melting (and the vast majority of them), an increase in pressure increases the melting point and vice versa. At water, the volume decreases during melting (therefore, when it freezes, water breaks pipes), and when pressure increases, ice melts at a lower temperature. Bismuth, gallium and some grades of cast iron behave in a similar way.
V. Gas- a condition characterized by good compressibility, the lack of the ability to maintain both volume and shape. Gas tends to occupy the entire volume provided to it. Atoms or molecules of a gas behave relatively freely, the distances between them are much greater than their size.
Plasma, often referred to as a state of aggregation of matter, differs from gas in a high degree of ionization of atoms. Most of the baryonic matter (by mass approx. 99.9%) in the Universe is in the plasma state.
g. C supercritical fluid- Occurs with a simultaneous increase in temperature and pressure to a critical point, at which the density of the gas is compared with the density of the liquid; in this case, the boundary between the liquid and gaseous phases disappears. The supercritical fluid has an exceptionally high dissolving power.
d. Bose-Einstein condensate- is obtained by cooling the Bose gas to temperatures close to absolute zero. As a result, some of the atoms are in a state with strictly zero energy (that is, in the lowest possible quantum state). The Bose-Einstein condensate exhibits a number of quantum properties such as superfluidity and Fischbach resonance.
e. Fermionic condensate- is a Bose-condensation in the BCS mode of "atomic Cooper pairs" in gases consisting of fermion atoms. (In contrast to the traditional mode of Bose-Einstein condensation of compound bosons).
Such fermionic atomic condensates are "relatives" of superconductors, but with a critical temperature of the order of room temperature and above.
Degenerate matter - Fermi gas 1st stage Electron degenerate gas, observed in white dwarfs, plays an important role in the evolution of stars. The 2nd stage is the neutron state where matter passes under ultrahigh pressure, which is unattainable in the laboratory yet, but exists inside neutron stars. During the transition to the neutron state, the electrons of matter interact with protons and turn into neutrons. As a result, matter in the neutron state consists entirely of neutrons and has a density of the order of nuclear. The temperature of the substance in this case should not be too high (in energy equivalent, not more than a hundred MeV).
With a strong increase in temperature (hundreds of MeV and above), in the neutron state, various mesons begin to be born and annihilate. With a further increase in temperature, deconfinement occurs, and the matter passes into the state of quark-gluon plasma. It no longer consists of hadrons, but of constantly born and disappearing quarks and gluons. Perhaps deconfinement occurs in two stages.
With a further unlimited increase in pressure without an increase in temperature, the matter collapses into a black hole.
With a simultaneous increase in both pressure and temperature, other particles are added to quarks and gluons. What happens to matter, space and time at temperatures close to the Planck temperature is still unknown.
Other states
During deep cooling, some (by no means all) substances pass into a superconducting or superfluid state. These states, of course, are separate thermodynamic phases, but they hardly deserve to be called new aggregate states of matter due to their non-universality.
Inhomogeneous substances such as pastes, gels, suspensions, aerosols, etc., which under certain conditions exhibit the properties of both solids and liquids and even gases, are usually classified as dispersed materials, and not to any specific aggregate states of matter .
Depending on temperature and pressure, any substance is capable of taking on various states of aggregation. Each such state is characterized by certain qualitative properties that remain unchanged within the framework of temperatures and pressures required for a given state of aggregation.
The characteristic properties of aggregate states include, for example, the ability of a body in a solid state to maintain its shape, or vice versa, the ability of a liquid body to change shape. However, sometimes the boundaries between different states of matter are quite blurred, as in the case of liquid crystals, or the so-called "amorphous bodies", which can be elastic like solids and fluid like liquids.
The transition between states of aggregation can occur with the release of free energy, changes in density, entropy, or other physical quantities. The transition from one state of aggregation to another is called a phase transition, and the phenomena accompanying such transitions are called critical phenomena.
List of known aggregate states
Solid |
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Solids whose atoms or molecules do not form a crystal lattice. |
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Solids whose atoms or molecules form a crystal lattice. |
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Mesophase |
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A liquid crystal is a phase state during which a substance simultaneously possesses both the properties of liquids and the properties of crystals. |
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Liquid |
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The state of matter at temperatures above the melting point and below the boiling point. |
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A liquid whose temperature exceeds its boiling point. |
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A liquid whose temperature is less than the crystallization temperature. |
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The state of a liquid substance under negative pressure caused by van der Waals forces (forces of attraction between molecules). |
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The state of a liquid at a temperature above the critical point. |
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A liquid whose properties are affected by quantum effects. |
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A state of matter that has very weak bonds between molecules or atoms. Does not lend itself to the mathematical description of an ideal gas. |
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A gas whose properties are affected by quantum effects. |
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Aggregate state, represented by a set of individual charged particles, the total charge of which in any volume of the system is equal to zero. |
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A state of matter in which it is a collection of gluons, quarks, and antiquarks. |
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A momentary state during which gluon force fields are stretched between nuclei. Preceded by quark-gluon plasma. |
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quantum gas |
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A gas composed of fermions whose properties are affected by quantum effects. |
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A gas composed of bosons whose properties are affected by quantum effects. |
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Everyone, I think, knows 3 basic aggregate states of matter: liquid, solid and gaseous. We encounter these states of matter every day and everywhere. Most often they are considered on the example of water. The liquid state of water is most familiar to us. We constantly drink liquid water, it flows from our tap, and we ourselves are 70% liquid water. The second aggregate state of water is ordinary ice, which we see on the street in winter. In gaseous form, water is also easy to meet in everyday life. In the gaseous state, water is, we all know, steam. It can be seen when we, for example, boil a kettle. Yes, it is at 100 degrees that water passes from a liquid state to a gaseous state.
These are the three aggregate states of matter familiar to us. But did you know that there are actually 4 of them? I think at least once everyone heard the word " plasma". And today I want you to also learn more about plasma - the fourth state of matter.
Plasma is a partially or fully ionized gas with the same density of both positive and negative charges. Plasma can be obtained from gas - from the 3rd state of matter by strong heating. The state of aggregation in general, in fact, completely depends on temperature. The first state of aggregation is the lowest temperature at which the body remains solid, the second state of aggregation is the temperature at which the body begins to melt and become liquid, the third state of aggregation is the highest temperature at which the substance becomes a gas. For each body, substance, the temperature of transition from one state of aggregation to another is completely different, for some it is lower, for some it is higher, but for everyone it is strictly in this sequence. And at what temperature does a substance become plasma? Since this is the fourth state, it means that the transition temperature to it is higher than that of each previous one. And indeed it is. In order to ionize a gas, a very high temperature is required. The lowest temperature and low ionized (about 1%) plasma is characterized by temperatures up to 100 thousand degrees. Under terrestrial conditions, such plasma can be observed in the form of lightning. The temperature of the lightning channel can exceed 30 thousand degrees, which is 6 times more than the surface temperature of the Sun. By the way, the Sun and all other stars are also plasma, more often still high-temperature. Science proves that about 99% of the entire matter of the Universe is plasma.
Unlike low-temperature plasma, high-temperature plasma has almost 100% ionization and temperatures up to 100 million degrees. This is truly stellar temperature. On Earth, such a plasma is found only in one case - for experiments on thermo-nuclear fusion. Con-tro-whether-ru-e-may the reaction is quite complex and energy-expensive, but non-con-tro-whether-ru-e-may is enough dawn-to-men-do -was itself like a weapon of an ear of greasy power - a thermo-nuclear bomb, tested by the USSR on August 12, 1953.
Plasma is classified not only by temperature and degree of ionization, but also by density and quasi-neutrality. phrase plasma density usually means electron density, that is, the number of free electrons per unit volume. Well, with this, I think everything is clear. But not everyone knows what quasi-neutrality is. The quasi-neutrality of a plasma is one of its most important properties, which consists in the almost exact equality of the densities of its constituent positive ions and electrons. Due to the good electrical conductivity of the plasma, the separation of positive and negative charges is impossible at distances greater than the Debye length and at times greater than the period of plasma oscillations. Almost all plasma is quasi-neutral. An example of a non-quasi-neutral plasma is an electron beam. However, the density of non-neutral plasmas must be very low, otherwise they will quickly decay due to Coulomb repulsion.
We have considered very little terrestrial examples of plasma. But there are enough of them. Man has learned to use plasma for his own good. Thanks to the fourth aggregate state of matter, we can use gas-discharge lamps, plasma televisions zo-rami, electric arc-welding, lasers. Ordinary gas-discharge fluorescent lamps are also plasma. There is also a plasma lamp in our world. It is mainly used in science to study and, most importantly, to see some of the most complex plasma phenomena, including filamentation. A photo of such a lamp can be seen in the picture below:
In addition to household plasma devices, natural plasma can also often be seen on Earth. We have already talked about one of its examples. This is lightning. But in addition to lightning, plasma phenomena can be called the northern lights, “the fires of St. Elmo”, the Earth's ionosphere and, of course, fire.
Notice that both fire and lightning and other manifestations of plasma, as we call it, burn. What is the reason for such a bright emission of light by plasma? Plasma glow is due to the transition of electrons from a high-energy state to a low-energy state after recombination with ions. This process leads to radiation with a spectrum corresponding to the excited gas. This is why plasma glows.
I would also like to tell a little about the history of plasma. After all, once upon a time only such substances as the liquid component of milk and the colorless component of blood were called plasma. Everything changed in 1879. It was in that year that the famous English scientist William Crookes, investigating electrical conductivity in gases, discovered the phenomenon of plasma. True, this state of matter was called plasma only in 1928. And this was done by Irving Langmuir.
In conclusion, I want to say that such an interesting and mysterious phenomenon as ball lightning, which I wrote about more than once on this site, is, of course, also a plasmoid, like ordinary lightning. This is perhaps the most unusual plasmoid of all terrestrial plasma phenomena. After all, there are about 400 very different theories about ball lightning, but not one of them has been recognized as truly correct. Under laboratory conditions, similar but short-term phenomena have been obtained in several different ways, so the question of the nature of ball lightning remains open.
Ordinary plasma, of course, was also created in laboratories. Once it was difficult, but now such an experiment is not difficult. Since plasma has firmly entered our household arsenal, there are a lot of experiments on it in laboratories.
The most interesting discovery in the field of plasma was experiments with plasma in weightlessness. It turns out that plasma crystallizes in a vacuum. It happens like this: the charged particles of the plasma begin to repel each other, and when they have a limited volume, they occupy the space that is allotted to them, scattering in different directions. This is very similar to a crystal lattice. Doesn't this mean that plasma is the closing link between the first aggregate state of matter and the third? After all, it becomes a plasma due to the ionization of the gas, and in a vacuum, the plasma again becomes, as it were, solid. But that's just my guess.
Plasma crystals in space also have a rather strange structure. This structure can be observed and studied only in space, in a real space vacuum. Even if you create a vacuum on the Earth and place a plasma there, then gravity will simply squeeze the entire “picture” that forms inside. In space, however, plasma crystals simply take off, forming a volumetric three-dimensional structure of a strange shape. After sending the results of observations of plasma in orbit to earth scientists, it turned out that the swirls in the plasma mimic the structure of our galaxy in a strange way. And this means that in the future it will be possible to understand how our galaxy was born by studying plasma. The photographs below show the same crystallized plasma.
That's all I would like to say on the topic of plasma. I hope it intrigues and surprises you. After all, this is truly an amazing phenomenon, or rather a state - the 4th state of aggregation of matter.
In everyday practice, one has to deal not separately with individual atoms, molecules and ions, but with real substances - an aggregate of a large number of 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 |
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| liquid |
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| 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 result 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 a 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.
Any substance consists of molecules, and its physical properties depend 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 a gas at the molecular level, we will see molecules randomly rushing about 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 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 are attached to each other by 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 random heap - amorphous bodies (this is precisely the structure of polymers, which look like tangled 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. With further cooling, the water freezes, becoming a solid body, 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.