Definition

Aggregate states substances (from the Latin aggrego - I attach, bind) are states of the same substance - solid, liquid, gaseous.

When transitioning from one state to another, an abrupt change in energy, entropy, density and other characteristics of the substance occurs.

Solids and liquids

Definition

Solids are bodies that have a constant shape and volume.

In them, the intermolecular distances are small and the potential energy of the molecules is comparable to the kinetic energy. Solids are divided into two types: crystalline and amorphous. Able thermodynamic equilibrium only crystalline bodies remain. Amorphous bodies essentially represent metastable states, which in their structure are close to nonequilibrium, slowly crystallizing liquids. In an amorphous body there is a very slow process of crystallization, the process of gradual transition of a substance into the 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 depend on the direction in space. Various processes, such as thermal conductivity, electrical conductivity, light, sound, propagate in different directions of a solid in different ways. Amorphous bodies (glass, resins, plastics) are isotropic, like liquids. The only difference between amorphous bodies and liquids is that the latter are fluid and static shear deformations are impossible in them.

Crystalline bodies have the correct molecular structure. The anisotropy of its properties is due to the correct structure of the crystal. The correct arrangement of atoms in a crystal forms what is called a crystal lattice. In different directions, the arrangement of atoms in the lattice is different, which leads to anisotropy. Atoms (or ions, or entire molecules) in a crystal lattice undergo random oscillatory motion around average positions, which are considered as nodes of the crystal lattice. The higher the temperature, the greater the oscillation energy, and therefore the average amplitude of oscillations. The size of the crystal depends on the amplitude of the oscillations. An increase in the amplitude of oscillations leads to an increase in body size. This explains the thermal expansion of solids.

Definition

Liquids are bodies that have a certain volume, but do not have elasticity of shape.

Liquids are characterized by strong intermolecular interactions and low compressibility. A liquid occupies an intermediate position between a solid and a gas. Liquids, like gases, are isotropic. In addition, the liquid has fluidity. In it, as in gases, there are no tangential stresses (shear stresses) of bodies. Liquids are heavy, i.e. their specific gravities are comparable to the specific gravities of solids. Near crystallization temperatures, their heat capacities and other thermal characteristics are close to the corresponding characteristics of solids. In liquids there is a certain degree of regular arrangement of atoms, but only in small areas. Here the atoms also undergo oscillatory motion near the nodes of the quasicrystalline cell, but unlike atoms in a solid body, they jump from one node to another from time to time. As a result, the movement of atoms will be very complex: it is oscillatory, but at the same time the center of oscillations moves in space.

Gas, evaporation, condensation and melting

Definition

Gas is a state of matter in which the distances between molecules are large.

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

Substances can change from one state of aggregation to another.

Definition

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

Evaporation is a phase transition. During evaporation, part of a liquid or solid turns into vapor. A substance in a gaseous state that is in dynamic equilibrium with a liquid is called saturated vapor. At the same time, the change internal energy body:

\[\triangle \U=\pm mr\ \left(1\right),\]

where m is body mass, r is the specific heat of vaporization (J/kg).

Definition

Condensation is the reverse process of evaporation.

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

Definition

Melting is the process of transition of a substance from a solid to a liquid state, the process of changing the aggregate state of a substance.

When a substance is heated, its internal energy increases, therefore, the speed of thermal movement of molecules increases. If the melting temperature of a substance is reached, the crystal lattice of the solid begins to collapse. The bonds between particles are destroyed, and the energy of interaction between particles increases. The heat transferred to the body goes to increase the internal energy of this body, and part of the energy goes to doing work to change the volume of the body when it melts. Most crystalline bodies the volume increases when melting, 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 accompanied by an abrupt change in heat capacity at the melting temperature. The melting point depends on the substance and does not change during the process. In this case, the change in the internal energy of the body:

\[\triangle U=\pm m\lambda \left(2\right),\]

where $\lambda$ is the specific heat of fusion (J/kg).

The reverse process to melting is crystallization. The change in internal energy is calculated using formula (2).

The change in internal energy of each body of the system in the case of heating or cooling can be calculated using the formula:

\[\triangle U=mc\triangle T\left(3\right),\]

where c - specific heat substance, J/(kgK), $\triangle T$ - change in body temperature.

When studying the transitions of substances from one state of aggregation to another, it is impossible to do without the so-called heat balance equation, which states: the total amount of heat that is released in a thermally insulated system is equal to the amount of heat (total) that is absorbed in this system.

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

Example 1

Assignment: A thermally insulated vessel contains water and ice at a temperature $t_i= 0^oС$. The mass of water ($m_(v\ ))$ and ice ($m_(i\ ))$ are respectively equal to 0.5 kg and 60 g. Water vapor with a mass of $m_(p\ )=$10 g is introduced into the water. at temperature $t_p= 100^oС$. What will be the temperature of the water in the vessel after thermal equilibrium is established? Ignore the heat capacity of the vessel.

Solution: Let's determine what processes occur in the system, what states of matter we had and what we received.

Water vapor condenses, giving off heat.

This the heat is coming to melt the ice and possibly heat the water available and obtained from the ice.

Let's first check how much heat is released when the existing mass of steam condenses:

here from reference materials we have $r=2.26 10^6\frac(J)(kg)$ - specific heat of vaporization (also applicable for condensation).

Heat required to melt ice:

here from reference materials we have $\lambda =3.3\cdot 10^5\frac(J)(kg)$ - specific heat of melting of ice.

We find that the steam gives off more heat than is required only to melt the existing ice, therefore we write the heat balance equation in the form:

Heat is released during condensation of steam with mass $m_(p\ )$ and cooling of water, which is formed from steam from temperature $T_p$ to the desired T. Heat is absorbed during melting of ice with mass $m_(i\ )$ and heating of water with mass $m_v+ m_i$ from temperature $T_i$ to $T.\ $ Let us denote $T-T_i=\triangle T$, for the difference $T_p-T$ we obtain:

The heat balance equation will take the form:

\ \ \[\triangle T=\frac(rm_(p\ )+cm_(p\ )100-lm_(i\ ))(c\left(m_v+m_i+m_(p\ )\right))\left (1.6\right)\]

Let's carry out the calculations, taking into account that the heat capacity of water is tabulated $c=4.2\cdot 10^3\frac(J)(kgK)$, $T_p=t_p+273=373K,$ $T_i=t_i+273=273K$:

$\triangle T=\frac(2.26\cdot 10^6\cdot 10^(-2)+4.2\cdot 10^3\cdot 10^(-2)10^2-6\cdot 10^ (-2)\cdot 3.3\cdot 10^5)(4.2\cdot 10^3\cdot 5.7\cdot 10^(-1))\approx 3\left(K\right)$then T=273+3=276 (K)

Answer: The temperature of the water in the vessel after thermal equilibrium is established will be 276 K.

Example 2

Assignment: The figure shows a section of the isotherm corresponding to the transition of a substance from a crystalline to a liquid state. What does this section correspond to? p,T diagram?

The entire set of states shown in the diagram p,V horizontal The line segment on the diagram p, T is represented by one point that determines the values ​​of p and T at which the transition from one state of aggregation to another occurs.

Substances can be in different states of aggregation: solid, liquid, gaseous. Molecular forces in different states of aggregation are different: in the solid state they are greatest, in the gaseous state they are the smallest. The difference in molecular forces explains properties that appear in different states of aggregation:

In solids, the distance between molecules is small and interaction forces predominate. Therefore, solids have the property of maintaining shape and volume. The molecules of solids are in constant motion, but each molecule moves around an equilibrium position.

In liquids, the distance between molecules is larger, which means that the interaction force is smaller. Therefore, the liquid retains its volume, but easily changes shape.

In gases, the interaction forces are very small, since the distance between gas molecules is several tens of times greater than the size of the molecules. Therefore, the gas occupies the entire volume provided to it.

Transitions from one state of matter to another

Definition

Melting of matter$-$ transition of a substance from a solid to a liquid state.

This phase transition is always accompanied by the absorption of energy, i.e., heat must be supplied to the substance. At the same time, the internal energy of the substance increases. Melting occurs only at a certain temperature, called the melting point. Each substance has its own melting point. For example, ice has $t_(pl)=0^0\textrm(C)$.

While melting occurs, the temperature of the substance does not change.

What needs to be done to melt a substance of mass $m$? First, you need to heat it to the melting temperature $t_(melt)$, giving the amount of heat $c(\cdot)m(\cdot)(\Delta)T$, where $c$ $-$ is the specific heat capacity of the substance. Then it is necessary to add the amount of heat $(\lambda)(\cdot)m$, where $\lambda$ $-$ is the specific heat of fusion of the substance. The melting itself will occur at a constant temperature equal to the melting point.

Definition

Crystallization (solidification) of a substance$-$ transition of a substance from a liquid to a solid state.

This is the reverse process of melting. Crystallization is always accompanied by the release of energy, i.e., heat must be removed from the substance. In this case, the internal energy of the substance decreases. It occurs only at a certain temperature, coinciding with the melting point.

While crystallization occurs, the temperature of the substance does not change.

What needs to be done for a substance of mass $m$ to crystallize? First, you need to cool it to the melting temperature $t_(melt)$, removing the amount of heat $c(\cdot)m(\cdot)(\Delta)T$, where $c$ $-$ is the specific heat capacity of the substance. Then it is necessary to remove the amount of heat $(\lambda)(\cdot)m$, where $\lambda$ $-$ is the specific heat of fusion of the substance. Crystallization will occur at a constant temperature equal to the melting point.

Definition

Vaporization of a substance$-$ transition of a substance from a liquid to a gaseous state.

This phase transition is always accompanied by the absorption of energy, i.e., heat must be supplied to the substance. At the same time, the internal energy of the substance increases.

There are two types of vaporization: evaporation and boiling.

Definition

Evaporation$-$ vaporization from the surface of a liquid, occurring at any temperature.

The rate of evaporation depends on:

    temperature;

    surface area;

    kind of liquid;

    wind.

Definition

Boiling$-$ vaporization throughout the entire volume of liquid, which occurs only at a certain temperature, called the boiling point.

Each substance has its own boiling point. For example, water has $t_(boiling)=100^0\textrm(C)$. While boiling occurs, the temperature of the substance does not change.

What must be done for a substance of mass $m$ to boil away? First you need to heat it to the boiling point $t_(boiling)$, giving the amount of heat $c(\cdot)m(\cdot)(\Delta)T$, where $c$ $-$ is the specific heat capacity of the substance. Then it is necessary to add the amount of heat $(L)(\cdot)m$, where $L$ $-$ is the specific heat of vaporization of the substance. The boiling itself will occur at a constant temperature equal to the boiling point.

Definition

Condensation of matter$-$ transition of a substance from a gaseous state to a liquid state.

This is the reverse process of vaporization. Condensation is always accompanied by the release of energy, i.e., heat must be removed from the substance. In this case, the internal energy of the substance decreases. It occurs only at a certain temperature, coinciding with the boiling point.

While condensation occurs, the temperature of the substance does not change.

What must be done for a substance of mass $m$ to condense? First you need to cool it to the boiling point $t_(boiling)$, removing the amount of heat $c(\cdot)m(\cdot)(\Delta)T$, where $c$ $-$ is the specific heat capacity of the substance. Then it is necessary to remove the amount of heat $(L)(\cdot)m$, where $L$ $-$ is the specific heat of vaporization of the substance. Condensation will occur at a constant temperature equal to the boiling point.

Aggregate states. Liquids. Phases in thermodynamics. Phase transitions.

Lecture 1.16

All substances can exist in three states of aggregation - solid, liquid And gaseous. Transitions between them are accompanied by an abrupt change in the series physical properties(density, thermal conductivity, etc.).

The state of aggregation depends on the physical conditions in which the substance is located. The existence of several states of aggregation in a substance is due to differences in the thermal motion of its molecules (atoms) and in their interaction under different conditions.

Gas- the state of aggregation of a substance in which the particles are not connected or are very weakly connected by interaction forces; the kinetic energy of the thermal motion of its particles (molecules, atoms) significantly exceeds the potential energy of interactions between them, therefore the particles move almost freely, completely filling the vessel in which they are located and taking its shape. In the gaseous state, a substance has neither its own volume nor its own shape. Any substance can be converted into a gas by changing pressure and temperature.

Liquid- state of aggregation of a substance, intermediate between solid and gaseous. It is characterized by high mobility of particles and small free space between them. This causes liquids to maintain their volume and take the shape of the container. In a liquid, the molecules are located very close to each other. Therefore, the density of liquid is much greater than the density of gases (at normal pressure). The properties of a liquid are the same (isotropic) in all directions, with the exception of liquid crystals. When heated or the density decreases, the properties of the liquid, thermal conductivity, and viscosity change, as a rule, towards the properties of gases.

The thermal motion of liquid molecules consists of a combination of collective vibrational movements and jumps of molecules that occur from time to time from one equilibrium position to another.

Solid (crystalline) bodies- the state of aggregation of a substance, characterized by stability of shape and the nature of the thermal movement of atoms. This movement is the vibration of the atoms (or ions) that make up the solid. The vibration amplitude is usually small compared to the interatomic distances.

Properties of liquids.

The molecules of a substance in a liquid state are located almost close to each other. Unlike solid crystalline bodies, in which molecules form ordered structures throughout the entire volume of the crystal and can perform thermal vibrations around fixed centers, liquid molecules have greater freedom. Each molecule of a liquid, just like in a solid, is “sandwiched” on all sides by neighboring molecules and undergoes thermal vibrations around a certain equilibrium position. However, from time to time any molecule may move to a nearby vacant site. Such jumps in liquids occur quite often; therefore, the molecules are not tied to specific centers, as in crystals, and can move throughout the entire volume of the liquid. This explains the fluidity of liquids. Due to the strong interaction between closely located molecules, they can form local (unstable) ordered groups containing several molecules. This phenomenon is called close order.



Due to the dense packing of molecules, the compressibility of liquids, i.e., the change in volume with a change in pressure, is very small; it is tens and hundreds of thousands of times less than in gases. For example, to change the volume of water by 1%, you need to increase the pressure approximately 200 times. This increase in pressure compared to atmospheric pressure is achieved at a depth of about 2 km.

Liquids, like solids, change their volume with changes in temperature. For not very large temperature ranges, the relative change in volume Δ V / V 0 is proportional to the temperature change Δ T:

The coefficient β is called temperature coefficient of volumetric expansion. This coefficient for liquids is tens of times greater than for solids. For water, for example, at a temperature of 20 °C β ≈ 2 10 –4 K –1, for steel - β st ≈ 3.6 10 –5 K –1, for quartz glass - β kV ≈ 9 10 – 6 K –1.

The thermal expansion of water has an interesting and important anomaly for life on Earth. At temperatures below 4 °C, water expands as the temperature decreases (β< 0). Максимум плотности ρ в = 10 3 кг/м 3 вода имеет при температуре 4 °С.

When water freezes, it expands, so ice remains floating on the surface of a freezing body of water. The temperature of freezing water under the ice is 0 °C. In denser layers of water at the bottom of the reservoir, the temperature is about 4 °C. Thanks to this, life can exist in the water of freezing reservoirs.

Most interesting feature liquids is the presence free surface. Liquid, unlike gases, does not fill the entire volume of the container into which it is poured. An interface is formed between liquid and gas (or vapor), which is located in special conditions compared to the rest of the liquid. Molecules in the boundary layer of a liquid, unlike molecules in its depth, are not surrounded by other molecules of the same liquid on all sides. The forces of intermolecular interaction acting on one of the molecules inside a liquid from neighboring molecules are, on average, mutually compensated. Any molecule in the boundary layer is attracted by molecules located inside the liquid (the forces acting on a given liquid molecule from gas (or vapor) molecules can be neglected). As a result, a certain resultant force appears, directed deep into the liquid. Surface molecules are drawn into the liquid by forces of intermolecular attraction. But all molecules, including molecules of the boundary layer, must be in a state of equilibrium. This equilibrium is achieved by slightly reducing the distance between the molecules of the surface layer and their nearest neighbors inside the liquid. As the distance between molecules decreases, repulsive forces arise. If the average distance between molecules inside a liquid is r 0, then the molecules of the surface layer are packed somewhat more densely, and therefore they have an additional reserve potential energy compared to internal molecules. It should be borne in mind that due to the extremely low compressibility, the presence of a more densely packed surface layer does not lead to any noticeable change in the volume of the liquid. If a molecule moves from the surface into the liquid, the forces of intermolecular interaction will do positive work. On the contrary, in order to pull a certain number of molecules from the depth of the liquid to the surface (i.e., increase the surface area of ​​the liquid), external forces must do positive work A external, proportional to the change Δ S surface area:

A ext = σΔ S.

The coefficient σ is called the coefficient surface tension(σ > 0). Thus, the coefficient of surface tension is equal to the work required to increase the surface area of ​​a liquid at constant temperature by one unit.

In SI, the coefficient of surface tension is measured in joules per meter square (J/m2) or in newtons per meter (1 N/m = 1 J/m2).

Consequently, the molecules of the surface layer of a liquid have an excess of potential energy. Potential energy E p of the liquid surface is proportional to its area: (1.16.1)

It is known from mechanics that the equilibrium states of a system correspond to the minimum value of its potential energy. It follows that the free surface of the liquid tends to reduce its area. For this reason, a free drop of liquid takes on a spherical shape. The liquid behaves as if forces acting tangentially to its surface are contracting (pulling) this surface. These forces are called surface tension forces.

The presence of surface tension forces makes the surface of a liquid look like an elastic stretched film, with the only difference that the elastic forces in the film depend on its surface area (i.e., on how the film is deformed), and the surface tension forces do not depend on the surface area liquids.

Surface tension forces tend to reduce the surface of the film. Therefore we can write: (1.16.2)

Thus, the surface tension coefficient σ can be defined as the modulus of the surface tension force acting per unit length of the line bounding the surface ( l- the length of this line).

Due to the action of surface tension forces in drops of liquid and inside soap bubbles, excess pressure Δ arises p. If you mentally cut a spherical drop of radius R into two halves, then each of them must be in equilibrium under the action of surface tension forces applied to the cut boundary of length 2π R and excess pressure forces acting on the area π R 2 sections (Fig. 1.16.1). The equilibrium condition is written as

Near the boundary between a liquid, a solid and a gas, the shape of the free surface of the liquid depends on the forces of interaction between liquid molecules and solid molecules (interaction with gas (or vapor) molecules can be neglected). If these forces are greater than the forces of interaction between the molecules of the liquid itself, then the liquid wets surface of a solid. In this case, the liquid approaches the surface of the solid body at some acute angleθ, characteristic of a given liquid-solid pair. The angle θ is called contact angle. If the forces of interaction between liquid molecules exceed the forces of their interaction with solid molecules, then the contact angle θ turns out to be obtuse (Fig. 1.16.2(2)). In this case they say that the liquid does not wet surface of a solid. Otherwise (angle - acute) liquid wets surface (Fig. 1.16.2(1)). At full wettingθ = 0, at complete non-wettingθ = 180°.

Capillary phenomena called the rise or fall of liquid in small diameter tubes - capillaries. Wetting liquids rise through the capillaries, non-wetting liquids descend.

Figure 1.16.3 shows a capillary tube of a certain radius r, lowered at the lower end into a wetting liquid of density ρ. The upper end of the capillary is open. The rise of liquid in the capillary continues until the force of gravity acting on the column of liquid in the capillary becomes equal in magnitude to the resultant F n surface tension forces acting along the boundary of contact of the liquid with the surface of the capillary: F t = F n, where F t = mg = ρ hπ r 2 g, F n = σ2π r cos θ.

This implies:

With complete wetting θ = 0, cos θ = 1. In this case

With complete non-wetting θ = 180°, cos θ = –1 and, therefore, h < 0. Уровень несмачивающей жидкости в капилляре опускается ниже уровня жидкости в сосуде, в которую опущен капилляр.

Water almost completely wets the clean glass surface. On the contrary, mercury does not completely wet the glass surface. Therefore, the level of mercury in the glass capillary drops below the level in the vessel.

Questions about what the state of aggregation is, what features and properties solids, liquids and gases have, are considered in several training courses. There are three classical states of matter, with their own characteristic structural features. Their understanding is an important point in understanding the sciences of the Earth, living organisms, and industrial activities. These questions are studied by physics, chemistry, geography, geology, physical chemistry and other scientific disciplines. Substances that, under certain conditions, are in one of three basic types of state can change with an increase or decrease in temperature and pressure. Let us consider possible transitions from one state of aggregation to another, as they occur in nature, technology and Everyday life.

What is a state of aggregation?

The word of Latin origin "aggrego" translated into Russian means "to join". The scientific term refers to the state of the same body, substance. The existence of solids, gases and liquids at certain temperatures and different pressures is characteristic of all the shells of the Earth. In addition to the three basic states of aggregation, there is also a fourth. At elevated temperature and constant pressure, the gas turns into plasma. To better understand what a state of aggregation is, it is necessary to remember tiny particles ah, from which substances and bodies are made.

The diagram above shows: a - gas; b—liquid; c is a solid body. In such pictures, circles indicate the structural elements of substances. This symbol, in fact, atoms, molecules, ions are not solid balls. Atoms consist of a positively charged nucleus around which negatively charged electrons move at high speed. Knowledge about the microscopic structure of matter helps to better understand the differences that exist between different aggregate forms.

Ideas about the microworld: from Ancient Greece to the 17th century

The first information about the particles that make up physical bodies, appeared in Ancient Greece. The thinkers Democritus and Epicurus introduced such a concept as the atom. They believed that these smallest indivisible particles of different substances have a shape, certain sizes, and are capable of movement and interaction with each other. Atomism became the most advanced teaching of ancient Greece for its time. But its development slowed down in the Middle Ages. Since then scientists were persecuted by the Roman Inquisition catholic church. Therefore, until modern times, there was no clear concept of what the state of matter was. Only after the 17th century did scientists R. Boyle, M. Lomonosov, D. Dalton, A. Lavoisier formulate the provisions of the atomic-molecular theory, which have not lost their significance today.

Atoms, molecules, ions - microscopic particles of the structure of matter

A significant breakthrough in understanding the microworld occurred in the 20th century, when the electron microscope was invented. Taking into account the discoveries made by scientists earlier, it was possible to put together a coherent picture of the microworld. Theories that describe the state and behavior of the smallest particles of matter are quite complex; they relate to the field of To understand the characteristics of different aggregate states of matter, it is enough to know the names and characteristics of the main structural particles that form different substances.

  1. Atoms are chemically indivisible particles. Saved in chemical reactions, but are destroyed in nuclear ones. Metals and many other substances of atomic structure have a solid state of aggregation under normal conditions.
  2. Molecules are particles that are broken down and formed in chemical reactions. oxygen, water, carbon dioxide, sulfur. The physical state of oxygen, nitrogen, sulfur dioxide, carbon, oxygen under normal conditions is gaseous.
  3. Ions are the charged particles that atoms and molecules become when they gain or lose electrons—microscopic negatively charged particles. Many salts have an ionic structure, for example table salt, iron sulfate and copper sulfate.

There are substances whose particles are located in space in a certain way. The ordered mutual position of atoms, ions, and molecules is called a crystal lattice. Typically, ionic and atomic crystal lattices are characteristic of solids, molecular - for liquids and gases. Diamond is distinguished by its high hardness. Its atomic crystal lattice is formed by carbon atoms. But soft graphite also consists of atoms of this chemical element. Only they are located differently in space. The usual state of aggregation of sulfur is solid, but at high temperatures the substance turns into a liquid and an amorphous mass.

Substances in a solid state of aggregation

Solids under normal conditions retain their volume and shape. For example, a grain of sand, a grain of sugar, salt, a piece of rock or metal. If you heat sugar, the substance begins to melt, turning into a viscous brown liquid. Let's stop heating and we'll get a solid again. This means that one of the main conditions for the transition of a solid into a liquid is its heating or an increase in the internal energy of the particles of the substance. The solid state of aggregation of salt, which is used for food, can also be changed. But to melt table salt, a higher temperature is needed than when heating sugar. The fact is that sugar consists of molecules, and table salt consists of charged ions that are more strongly attracted to each other. Solids in liquid form do not retain their shape because the crystal lattices are destroyed.

The liquid aggregate state of the salt upon melting is explained by the breaking of bonds between the ions in the crystals. Charged particles are released that can carry electric charges. Molten salts conduct electricity and are conductors. In the chemical, metallurgical and engineering industries, solid substances are converted into liquids to obtain new compounds from them or to give them different shapes. Metal alloys have become widespread. There are several ways to obtain them, associated with changes in the state of aggregation of solid raw materials.

Liquid is one of the basic states of aggregation

If you pour 50 ml of water into a round-bottomed flask, you will notice that the substance will immediately take the shape of a chemical vessel. But as soon as we pour the water out of the flask, the liquid will immediately spread over the surface of the table. The volume of water will remain the same - 50 ml, but its shape will change. The listed features are characteristic of the liquid form of existence of matter. Many organic substances are liquids: alcohols, vegetable oils, acids.

Milk is an emulsion, i.e. a liquid containing droplets of fat. A useful liquid resource is oil. It is extracted from wells using drilling rigs on land and in the ocean. Sea water is also a raw material for industry. Its difference from fresh water rivers and lakes lies in the content of dissolved substances, mainly salts. When evaporating from the surface of reservoirs, only H 2 O molecules pass into a vapor state, dissolved substances remain. Methods for obtaining useful substances from sea ​​water and methods for cleaning it.

When the salts are completely removed, distilled water is obtained. It boils at 100°C and freezes at 0°C. Brines boil and turn into ice at other temperatures. For example, water in Northern Arctic Ocean freezes at a surface temperature of 2 °C.

The physical state of mercury under normal conditions is liquid. This silvery-gray metal is commonly used to fill medical thermometers. When heated, the mercury column rises on the scale and the substance expands. Why is alcohol tinted with red paint used, and not mercury? This is explained by the properties of liquid metal. At 30-degree frosts, the state of aggregation of mercury changes, the substance becomes solid.

If the medical thermometer breaks and the mercury spills out, then collecting the silver balls with your hands is dangerous. It is harmful to inhale mercury vapor; this substance is very toxic. In such cases, children need to turn to their parents and adults for help.

Gaseous state

Gases are unable to maintain either their volume or shape. Fill the flask to the top with oxygen (its chemical formula O 2). As soon as we open the flask, the molecules of the substance will begin to mix with the air in the room. This occurs due to Brownian motion. Even the ancient Greek scientist Democritus believed that particles of matter are in constant motion. In solids, under normal conditions, atoms, molecules, and ions do not have the opportunity to leave crystal lattice, free yourself from connections with other particles. This is only possible when a large amount of energy is supplied from outside.

In liquids, the distance between particles is slightly greater than in solids; they require less energy to break intermolecular bonds. For example, the liquid state of oxygen is observed only when the gas temperature decreases to −183 °C. At −223 °C, O 2 molecules form a solid. When the temperature rises above these values, oxygen turns into gas. It is in this form that it is found under normal conditions. Industrial enterprises operate special installations for separating atmospheric air and obtaining nitrogen and oxygen from it. First, the air is cooled and liquefied, and then the temperature is gradually increased. Nitrogen and oxygen turn into gases under different conditions.

The Earth's atmosphere contains 21% by volume oxygen and 78% nitrogen. These substances are not found in liquid form in the gaseous shell of the planet. Liquid oxygen is light blue in color and is used to fill cylinders at high pressure for use in medical settings. In industry and construction, liquefied gases are needed to carry out many processes. Oxygen is needed for gas welding and cutting of metals, in chemistry - for oxidation reactions of inorganic and organic matter. If you open the valve of an oxygen cylinder, the pressure decreases and the liquid turns into gas.

Liquefied propane, methane and butane are widely used in energy, transport, industry and household activities. These substances are obtained from natural gas or during cracking (splitting) of petroleum feedstock. Carbon liquid and gaseous mixtures play an important role in the economies of many countries. But oil and natural gas reserves are severely depleted. According to scientists, this raw material will last for 100-120 years. An alternative source of energy is air flow (wind). Fast-flowing rivers and tides on the shores of seas and oceans are used to operate power plants.

Oxygen, like other gases, can be in the fourth state of aggregation, representing a plasma. Unusual transition from solid to gaseous state - characteristic crystalline iodine. The dark purple substance undergoes sublimation - it turns into a gas, bypassing the liquid state.

How are transitions made from one aggregate form of matter to another?

Changes in the aggregate state of substances are not associated with chemical transformations; these are physical phenomena. As the temperature increases, many solids melt and turn into liquids. A further increase in temperature can lead to evaporation, that is, to the gaseous state of the substance. In nature and economy, such transitions are characteristic of one of the main substances on Earth. Ice, liquid, steam are states of water under different external conditions. The compound is the same, its formula is H 2 O. At a temperature of 0 ° C and below this value, water crystallizes, that is, turns into ice. As the temperature rises, the resulting crystals are destroyed - the ice melts, and liquid water is again obtained. When it is heated, evaporation is formed - the transformation of water into gas - even at low temperatures. For example, frozen puddles gradually disappear because the water evaporates. Even in frosty weather, wet laundry dries, but this process takes longer than on a hot day.

All of the listed transitions of water from one state to another are of great importance for the nature of the Earth. Atmospheric phenomena, climate and weather are associated with the evaporation of water from the surface of the World Ocean, the transfer of moisture in the form of clouds and fog to land, and precipitation (rain, snow, hail). These phenomena form the basis of the World water cycle in nature.

How do the aggregate states of sulfur change?

Under normal conditions, sulfur is bright shiny crystals or light yellow powder, i.e. it is a solid substance. The physical state of sulfur changes when heated. First, when the temperature rises to 190 °C, the yellow substance melts, turning into a mobile liquid.

If you quickly pour liquid sulfur into cold water, you get a brown amorphous mass. With further heating of the sulfur melt, it becomes more and more viscous and darkens. At temperatures above 300 °C, the state of aggregation of sulfur changes again, the substance acquires the properties of a liquid and becomes mobile. These transitions arise due to the ability of the atoms of an element to form chains of different lengths.

Why can substances be in different physical states?

Aggregate state of sulfur - simple substance- solid under normal conditions. Sulfur dioxide is a gas sulfuric acid- an oily liquid is heavier than water. Unlike salt and nitric acids it is not volatile, molecules do not evaporate from its surface. What state of aggregation does plastic sulfur have, which is obtained by heating crystals?

In its amorphous form, the substance has the structure of a liquid, with insignificant fluidity. But plastic sulfur simultaneously retains its shape (as a solid). There are liquid crystals that have a number of characteristic properties of solids. Thus, the state of a substance under different conditions depends on its nature, temperature, pressure and other external conditions.

What features exist in the structure of solids?

The existing differences between the basic aggregate states of matter are explained by the interaction between atoms, ions and molecules. For example, why does the solid state of matter lead to the ability of bodies to maintain volume and shape? In the crystal lattice of a metal or salt, structural particles are attracted to each other. In metals, positively charged ions interact with what is called an “electron gas,” a collection of free electrons in a piece of metal. Salt crystals arise due to the attraction of oppositely charged particles - ions. The distance between the above structural units of solids is much smaller than the sizes of the particles themselves. In this case, electrostatic attraction acts, it imparts strength, but repulsion is not strong enough.

To destroy the solid state of aggregation of a substance, effort must be made. Metals, salts, and atomic crystals melt at very high temperatures. For example, iron becomes liquid at temperatures above 1538 °C. Tungsten is refractory and is used to make incandescent filaments for light bulbs. There are alloys that become liquid at temperatures above 3000 °C. Many on Earth are in a solid state. These raw materials are extracted using technology in mines and quarries.

To separate even one ion from a crystal it is necessary to spend a large number of energy. But it is enough to dissolve salt in water for the crystal lattice to disintegrate! This phenomenon is explained amazing properties water as a polar solvent. H 2 O molecules interact with salt ions, destroying the chemical bond between them. Thus, dissolution is not a simple mixing of different substances, but a physicochemical interaction between them.

How do liquid molecules interact?

Water can be a liquid, a solid, and a gas (steam). These are its basic states of aggregation under normal conditions. Water molecules consist of one oxygen atom to which two hydrogen atoms are bonded. Polarization occurs chemical bond in a molecule, a partial negative charge appears on the oxygen atoms. Hydrogen becomes the positive pole in the molecule, attracted by the oxygen atom of another molecule. This is called "hydrogen bonding".

The liquid state of aggregation is characterized by distances between structural particles comparable to their sizes. Attraction exists, but it is weak, so the water does not retain its shape. Vaporization occurs due to the destruction of bonds that occurs on the surface of the liquid even at room temperature.

Do intermolecular interactions exist in gases?

The gaseous state of a substance differs from liquid and solid in a number of parameters. There are large gaps between the structural particles of gases, much larger than the sizes of molecules. In this case, the forces of attraction do not act at all. The gaseous state of aggregation is characteristic of substances present in the air: nitrogen, oxygen, carbon dioxide. In the picture below, the first cube is filled with gas, the second with liquid, and the third with solid.

Many liquids are volatile; molecules of the substance break off from their surface and go into the air. For example, if the opening of an open bottle with hydrochloric acid bring a cotton swab dipped in ammonia, white smoke appears. A chemical reaction between hydrochloric acid and ammonia occurs right in the air, producing ammonium chloride. What state of aggregation is this substance in? Its particles that form white smoke are tiny solid crystals of salt. This experiment must be carried out under a hood; the substances are toxic.

Conclusion

The state of aggregation of gas was studied by many outstanding physicists and chemists: Avogadro, Boyle, Gay-Lussac, Clayperon, Mendeleev, Le Chatelier. Scientists have formulated laws that explain the behavior of gaseous substances in chemical reactions when external conditions change. Open patterns were not only included in school and university textbooks on physics and chemistry. Many chemical industries are based on knowledge about the behavior and properties of substances in different states of aggregation.

I think everyone knows the 3 main states of matter: liquid, solid and gaseous. We encounter these states of matter every day and everywhere. Most often they are considered using 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 physical state of water is ordinary ice, which we see on the street in winter. Water is also easy to find in gaseous form in everyday life. In the gaseous state, water is, as we all know, steam. It can be seen when, for example, we boil a kettle. Yes, it is at 100 degrees that water changes from liquid to gaseous.

These are the three states of matter that are familiar to us. But did you know that there are actually 4 of them? I think everyone has heard the word “plasma” at least once. 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 equal densities of both positive and negative charges. Plasma can be obtained from gas - from the 3rd state of aggregation of a substance 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. At what temperature does a substance become plasma? Since this is the fourth state, it means that the temperature of transition 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 a temperature of 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 higher than the temperature of the surface of the Sun. By the way, the Sun and all other stars are also plasma, most often high-temperature. Science proves that about 99% of all matter in the Universe is plasma.

Unlike low-temperature plasma, high-temperature plasma has almost 100% ionization and a temperature of up to 100 million degrees. This is truly a stellar temperature. On Earth, such plasma is found only in one case - for thermonuclear fusion experiments. A controlled reaction is quite complex and energy-consuming, but an uncontrolled reaction has proven itself to be a weapon of colossal power - a thermonuclear 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. Collocation 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. Plasma quasineutrality is one of its most important properties, which consists in the almost exact equality of the densities of the positive ions and electrons included in its composition. Due to the good electrical conductivity of 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 small, otherwise they will quickly decay due to Coulomb repulsion.

We have looked at very few terrestrial examples of plasma. But there are quite a lot of them. Man has learned to use plasma for his own benefit. Thanks to the fourth state of matter, we can use gas-discharge lamps, plasma TVs, electric arc welding, and lasers. Conventional fluorescent discharge lamps are also plasma. There is also a plasma lamp in our world. It is mainly used in science to study and, most importantly, see some of the most complex plasma phenomena, including filamentation. A photograph 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 her examples. This is lightning. But in addition to lightning, plasma phenomena can be called the northern lights, “St. Elmo’s fire,” the Earth’s ionosphere and, of course, fire.

Notice that fire, lightning, and other manifestations of plasma, as we call it, burn. What causes such a bright light emission from plasma? Plasma glow is caused by the transition of electrons from a high-energy state to a low-energy state after recombination with ions. This process results in radiation with a spectrum corresponding to the excited gas. This is why plasma glows.

I would also like to talk 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, while studying 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 have written 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 different theories about ball lightning, but not one of them has been recognized as truly correct. In laboratory conditions, similar but short-term phenomena were obtained by several different ways, so the question about the nature of ball lightning remains open.

Ordinary plasma, of course, was also created in laboratories. This was once difficult, but now such an experiment is not particularly difficult. Since plasma has firmly entered our everyday arsenal, they are experimenting a lot on it in laboratories.

The most interesting discovery in the field of plasma was experiments with plasma in zero gravity. It turns out that plasma crystallizes in a vacuum. It happens like this: charged plasma particles 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 quite similar to a crystal lattice. Doesn't this mean that plasma is the closing link between the first 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 if solid. But this is just my guess.

Plasma crystals in space also have a rather strange structure. This structure can only be observed and studied in space, in the real vacuum of space. Even if you create a vacuum on Earth and place plasma there, gravity will simply compress the entire “picture” that forms inside. In space, plasma crystals simply take off, forming a three-dimensional three-dimensional structure strange shape. After sending the results of observing plasma in orbit to scientists on Earth, it turned out that the vortices in the plasma strangely repeat the structure of our galaxy. 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.