Basic general education

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

Introduction: state of matter

The mysterious world around us never ceases to amaze. An ice cube thrown into a glass and left at room temperature will turn into liquid in a matter of minutes, and if you leave this liquid on the windowsill for a longer time, it will completely evaporate. This is the simplest way to observe transitions from one state of matter to another.

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

How and why do these amazing transformations happen? To understand this, remember that everything around is made up of. Atoms and molecules of various substances interact with each other, and it is the bond between them that determines what is the substance's state of aggregation?.

There are four types of aggregate substances:

gaseous

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

Gaseous state

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

Unfortunately, it is impossible to see gas molecules with the naked eye or even with a light microscope. However, you can touch the gas. Of course, if you just try to catch gas molecules flying around in the palm of your hand, then you will not succeed. But probably everyone has seen (or done it themselves) how someone pumped air into a car or bicycle tire, and from soft and wrinkled it became inflated and elastic. And the apparent “weightlessness” of gases will be refuted by the experience described on page 39 of the textbook “Chemistry 7th grade” edited by O.S. Gabrielyan.

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

But if the gas occupies the entire volume provided to it, Why then doesn’t it fly into space and spread throughout the universe, filling interstellar space? So, does something still hold and limit gases to the planet’s atmosphere?

Absolutely right. And this - gravity. In order to break away from a planet and fly away, molecules need to reach speeds greater than escape velocity, or escape velocity, and the vast majority of molecules move much slower.

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

The collection contains questions and tasks of various types: calculation, qualitative and graphic; technical, practical and historical nature. The tasks are distributed by topic in accordance with the structure of the textbook “Physics. 9th grade” by A.V. Peryshkina, E.M. Gutnik and make it possible to implement the requirements stated by the Federal State Educational Standard for meta-subject, subject and personal learning outcomes.

Liquid state

By increasing pressure and/or decreasing temperature, gases can be converted to a liquid state. At the dawn of the 19th century, the English physicist and chemist Michael Faraday managed to transform chlorine and carbon dioxide into a liquid state by compressing them at very low temperatures. However, some of the gases did not yield to scientists at that time, and, as it turned out, the problem was not insufficient pressure, but in the inability to reduce the temperature to the required minimum.

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

If a drop of water remains on the surface, it will disappear after some time. But we remember that thanks to the law of conservation of mass-energy, nothing disappears or disappears without a trace. The liquid will evaporate, i.e. will change its state of aggregation to gaseous.

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

Evaporation from the surface of solids is called sublimation or sublimation. The easiest way to observe sublimation is to use naphthalene to combat moths. If you smell a liquid or solid, evaporation is occurring. After all, the nose is what catches the fragrant molecules of the substance.

Liquids surround humans everywhere. The properties of liquids are also familiar to everyone - viscosity and fluidity. When it comes to talking about the shape of a liquid, many people say that the liquid does not have a specific shape. But this only happens on Earth. Due to the force of gravity, a drop of water is deformed.

However, many have seen how astronauts in zero gravity conditions catch water balls of different sizes. In the absence of gravity, the liquid takes the shape of a sphere. And the force of surface tension provides the liquid with a spherical shape. Soap bubbles are a great way to become familiar with the force of surface tension on Earth.

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

Solid state

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

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

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

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

molecular,

metal.

For some substances change in states of aggregation occurs easily, as, for example, with water; other substances require special conditions (pressure, temperature). But in modern physics, scientists identify another independent state of matter - plasma.

Plasma - ionized gas with equal densities of both positive and negative charges. In living nature, plasma occurs in the sun or during a flash of lightning. The Northern Lights and even the familiar fire that warms us with its warmth during an outing into nature also belong to plasma.

Artificially created plasma adds brightness to any city. Neon lights are just low-temperature plasma in glass tubes. Our usual fluorescent lamps are also filled with plasma.

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

Low-temperature plasma in our usual fluorescent lamps is widely used in everyday life.

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

Buy

To check your understanding of the material, we offer a short test.

1. What does not apply to states of aggregation:

liquid

light +

2. The viscosity of Newtonian liquids obeys:

Boyle-Mariotte law

Archimedes' law

Newton's law of viscosity +

3. Why doesn’t the Earth’s atmosphere escape into outer space:

because gas molecules cannot reach escape velocity

because the gas molecules are affected by the force of gravity +

both answers are correct

4. What does not apply to amorphous substances:

sealing wax
iron +

5.When cooling, the volume increases at:

ice +

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Aggregate states of matter (from the Latin aggrego - I attach, connect) - these are states of the same substance, transitions between which correspond to abrupt changes in free energy, entropy, density and other physical parameters of the substance.

Gas (French gaz, derived from the Greek chaos - chaos) is a state of aggregation of a substance in which the forces of interaction of its particles, filling the entire volume provided to them, are negligible. In gases, intermolecular distances are large and molecules move almost freely.

Gases can be considered as significantly superheated or undersaturated vapors.
There is vapor above the surface of each liquid due to evaporation. When the vapor pressure increases to a certain limit, called saturated vapor pressure, the evaporation of the liquid stops, since the pressure of the vapor and liquid becomes the same.
A decrease in the volume of saturated steam causes condensation of part of the steam, rather than an increase in pressure. Therefore, the vapor pressure cannot be higher than the saturated vapor pressure. The saturation state is characterized by the saturation mass contained in 1m mass of saturated vapor, which depends on temperature. Saturated steam can become unsaturated if its volume is increased or its temperature is increased. If the temperature of the steam is much higher than the boiling point corresponding to a given pressure, the steam is called superheated.

Plasma is a partially or fully ionized gas in which the densities of positive and negative charges are almost equal. The sun, stars, clouds of interstellar matter consist of gases - neutral or ionized (plasma). Unlike other states of aggregation, plasma is a gas of charged particles (ions, electrons), which electrically interact with each other over large distances, but have neither short-range nor long-range orders in the arrangement of particles.

Liquid - this is the state of aggregation of a substance, intermediate between solid and gaseous.

Liquids have some features of a solid (retains its volume, forms a surface, has a certain tensile strength) and a gas (takes the shape of the vessel in which it is located).
The thermal motion of molecules (atoms) of a liquid is a combination of small vibrations around equilibrium positions and frequent jumps from one equilibrium position to another.
At the same time, slow movements of molecules and their vibrations occur within small volumes, frequent jumps of molecules disrupt the long-range order in the arrangement of particles and determine the fluidity of liquids, and small vibrations around equilibrium positions determine the existence of short-range order in liquids.

Liquids and solids, unlike gases, can be considered highly condensed media. In them, molecules (atoms) are located much closer to each other and the interaction forces are several orders of magnitude greater than in gases. Therefore, liquids and solids have significantly limited possibilities for expansion; they obviously cannot occupy an arbitrary volume, and at constant pressure and temperature they retain their volume, no matter what volume they are placed in. Transitions from a more structurally ordered state of aggregation to a less ordered state can also occur continuously. In this regard, instead of the concept of a state of aggregation, it is advisable to use a broader concept - the concept of phase.

Phase is the collection of all parts of a system that have the same chemical composition and are in the same state. This is justified by the simultaneous existence of thermodynamically equilibrium phases in a multiphase system: liquid with its saturated vapor; water and ice at melting point; two immiscible liquids (a mixture of water with triethylamine), differing in concentrations; the existence of amorphous solids that retain the structure of a liquid (amorphous state).

Amorphous solid state of matter is a type of supercooled state of liquid and differs from ordinary liquids in its significantly higher viscosity and numerical values of kinetic characteristics.

Crystalline solid state of matter is a state of aggregation that is characterized by large interaction forces between particles of matter (atoms, molecules, ions). Particles of solids oscillate around average equilibrium positions, called lattice nodes; the structure of these substances is characterized by a high degree of order (long- and short-range order) - order in the arrangement (coordination order), in the orientation (orientational order) of structural particles, or order in physical properties (for example, in the orientation of magnetic moments or electric dipole moments). The region of existence of the normal liquid phase for pure liquids, liquid and liquid crystals is limited from low temperatures by phase transitions, respectively, into the solid (crystallization), superfluid and liquid-anisotropic state.

State	Properties
Gaseous	1. The ability to take on the volume and shape of a vessel. 2. Compressibility. 3. Fast diffusion (chaotic movement of molecules). 4. E kinetic. > E potential
	1. The ability to take the shape of that part of the vessel that the substance occupies. 2. Failure to expand to fill the vessel. 3. Low compressibility. 4. Slow diffusion. 5. Fluidity. 6. E kinetic. = E potential
	1. The ability to maintain the characteristic shape and volume. 2. Low compressibility (under pressure). 3. Very slow diffusion due to oscillatory movements of particles. 4. No turnover. 5. E kinetic.< Е потенц.

The state of aggregation of a substance is determined by the forces acting between molecules, the distance between particles and the nature of their movement.

IN hard state, the particles occupy a certain position relative to each other. It has low compressibility and mechanical strength, since the molecules do not have freedom of movement, but only vibration. The molecules, atoms, or ions that form a solid are called structural units. Solids are divided into amorphous and crystalline(Table 27 ).

Table 33

Comparative characteristics of amorphous and crystalline substances

Substance

Characteristic

Amorphous

1. Short-range order of particle arrangement.

2. Isotropy of physical properties.

3. No specific melting point.

4. Thermodynamic instability (large reserve of internal energy).

5. Fluidity.

Examples: amber, glass, organic polymers, etc.

Crystalline

1. Long-range order of particle arrangement.

2. Anisotropy of physical properties.

3. Specific melting point.

4. Thermodynamic stability (low internal energy reserve).

5. There are elements of symmetry.

Examples: metals, alloys, solid salts, carbon (diamond, graphite), etc.

Crystalline substances melt at a strictly defined temperature (Tm), amorphous substances do not have a clearly defined melting point; when heated, they soften (characterized by a softening interval) and pass into a liquid or viscous state. The internal structure of amorphous substances is characterized by a random arrangement of molecules . The crystalline state of a substance presupposes the correct arrangement in space of the particles that make up the crystal, and the formation crystalline (spatial)grates. The main feature of crystalline bodies is their anisotropy - dissimilarity of properties (thermal and electrical conductivity, mechanical strength, dissolution rate, etc.) in different directions, while amorphous bodies isotropic .

Solidcrystals- three-dimensional formations characterized by strict repeatability of the same structural element (unit cell) in all directions. Unit cell- represents the smallest volume of a crystal in the form of a parallelepiped, repeated in the crystal an infinite number of times.

Basic parameters of the crystal lattice:

Energy of the crystal lattice (E cr. , kJ/mol) – This is the energy that is released during the formation of 1 mole of a crystal from microparticles (atoms, molecules, ions) that are in a gaseous state and separated from each other at a distance that precludes their interaction.

Lattice constant ( d , [ A 0 ]) – the smallest distance between the center of two particles in a crystal connected by a chemical bond.

Coordination number (c.n.) – the number of particles surrounding the central particle in space, connected to it by a chemical bond.

The points at which crystal particles are located are called crystal lattice nodes

Despite the variety of crystal shapes, they can be classified. Systematization of crystal forms was introduced A.V. Gadolin(1867), it is based on the features of their symmetry. In accordance with the geometric shape of crystals, the following systems (systems) are possible: cubic, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal and rhombohedral (Fig. 18).

The same substance can have different crystalline forms, which differ in internal structure, and therefore in physical and chemical properties. This phenomenon is called polymorphism . Isomorphism – two substances of different nature form crystals of the same structure. Such substances can replace each other in the crystal lattice, forming mixed crystals.

Rice. 18. Basic crystal systems.

Depending on the type of particles located at the nodes of the crystal lattice and the type of bonds between them, crystals are of four types: ionic, atomic, molecular and metallic(rice . 19).

Rice. 19. Types of crystals

Characteristics of crystal lattices are presented in table. 34.

A feature of hydraulic and pneumatic drives is that to create forces, torques and movements in machines, these types of drives use the energy of liquid, air or other gas, respectively.

The fluid used in the hydraulic drive is called working fluid (WF).

To understand the features of the use of liquids and gases in drives, it is necessary to recall some basic information about the aggregate states of matter, known from a physics course.

According to modern views, aggregate states of matter (from the Latin aggrego - I attach, bind) are understood as states of the same substance, transitions between which correspond to abrupt changes in free energy, entropy, density and other physical parameters of this substance.

In physics, it is customary to distinguish between four aggregate states of matter: solid, liquid, gaseous and plasma.

SOLID STATE(crystalline solid state of matter) is a state of aggregation that is characterized by large interaction forces between particles of matter (atoms, molecules, ions). Particles of solids oscillate around average equilibrium positions, called lattice nodes; the structure of these substances is characterized by a high degree of order (long- and short-range order) - order in the arrangement (coordination order), in the orientation (orientational order) of structural particles or order in physical properties.

LIQUID STATE- this is the state of aggregation of a substance, intermediate between solid and gaseous. Liquids have some features of a solid (retains its volume, forms a surface, has a certain tensile strength) and a gas (takes the shape of the vessel in which it is located). The thermal motion of molecules (atoms) of a liquid is a combination of small vibrations around equilibrium positions and frequent jumps from one equilibrium position to another. At the same time, slow movements of molecules and their vibrations occur within small volumes. Frequent jumps of molecules disrupt the long-range order in the arrangement of particles and determine the fluidity of liquids, and small vibrations around equilibrium positions determine the existence of short-range order in liquids.

GASEOUS STATE(from the French gaz, which in turn came from the Greek chaos - chaos) is a state of aggregation of a substance in which the forces of interaction of its particles, filling the entire volume provided to them, are negligible. In gases, intermolecular distances are large and molecules move almost freely.

Gases can be considered as significantly superheated or low-saturated vapors of liquids. There is vapor above the surface of each liquid due to evaporation. When the vapor pressure increases to a certain limit, called saturated vapor pressure, the evaporation of the liquid stops, since the pressure of the vapor and liquid becomes the same. A decrease in the volume of saturated steam causes condensation of part of the steam, rather than an increase in pressure. Therefore, the vapor pressure cannot be higher than the saturated vapor pressure. The saturation state is characterized by the saturation mass contained in 1 m3 of saturated steam mass, which depends on temperature. Saturated steam can become unsaturated if its volume is increased or its temperature is increased. If the temperature of the steam is much higher than the boiling point corresponding to a given pressure, the steam is called superheated.

PLASMA is a partially or fully ionized gas in which the densities of positive and negative charges are almost equal. The sun, stars, clouds of interstellar matter consist of gases - neutral or ionized (plasma). Unlike other states of aggregation, plasma is a gas of charged particles (ions, electrons), which electrically interact with each other over large distances, but have neither short-range nor long-range orders in the arrangement of particles.

As can be seen from the above, liquids are capable of maintaining volume, but are not able to independently maintain shape. The first property brings liquid closer to a solid, the second - to a gas. Both of these properties are not absolute. All liquids are compressible, although much less so than gases. All liquids resist changing shape, the displacement of one part of the volume relative to another, although less than solids.

Depending on temperature and pressure, any substance is capable of taking on different states of aggregation. Each such state is characterized by certain qualitative properties that remain unchanged within the temperatures and pressures required for a given state of aggregation.

The characteristic properties of states of aggregation include, for example, the ability of a body in a solid state to retain 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 so-called “amorphous solids”, which can be elastic like solids and fluid like liquids.

The transition between states of aggregation can occur with the release of free energy, a change 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 states of aggregation

Solid
	Solids whose atoms or molecules do not form a crystal lattice.
	Solids whose atoms or molecules form a crystal lattice.
Mesophase
	A liquid crystal is a phase state during which a substance simultaneously possesses both the properties of liquids and the properties of crystals.
Liquid
	The state of a substance at temperatures above the melting point and below the boiling point.
	A liquid whose temperature exceeds its boiling point.
	A liquid whose temperature is less than the crystallization temperature.
	The state of a liquid substance under negative pressure caused by van der Waals forces (forces of attraction between molecules).
	The state of a liquid at a temperature above the critical point.
	A liquid whose properties are influenced by quantum effects.
		The state of a substance that has very weak bonds between molecules or atoms. An ideal gas cannot be described mathematically.
	A gas whose properties are influenced by quantum effects.
		A state of aggregation represented by a set of individual charged particles, the total charge of which in any volume of the system is zero.
	A state of matter in which it is a collection of gluons, quarks and antiquarks.
	A short-lived state during which gluon force fields are stretched between nuclei. Precedes quark-gluon plasma.
Quantum gas
	A gas composed of fermions whose properties are influenced by quantum effects.
	A gas composed of bosons whose properties are influenced by quantum effects.