In nature, substances are found in three states: solid, liquid and gaseous. For example, water can be in a solid (ice), liquid (water) and gaseous (water vapor) state. In the thermometer you are familiar with, mercury is a liquid. There are mercury vapors above the surface, and at a temperature of -39 C, mercury turns into a solid.
In different states, substances have different properties. Most of the bodies around us are made of solids. These are houses, cars, tools, etc. The shape of a solid body can be changed, but this requires effort. For example, to bend a nail, you need to apply quite a lot of force.
IN normal conditions it is difficult to compress or stretch a solid body.
To give solids the desired shape and volume in plants and factories they are processed on special machines: lathes, planers, grinders.
A solid has its own shape and volume.
Unlike solids, liquids easily change their shape. They take the shape of the vessel in which they are located.
For example, the milk that fills a bottle is shaped like a bottle. When poured into a glass, it takes the shape of a glass (Fig. 13). But, changing shape, the liquid retains its volume.
Under normal conditions, only small droplets of liquid have their own shape - the shape of a ball. These are, for example, raindrops or drops into which a stream of liquid breaks up.
The production of objects from molten glass is based on the property of a liquid to easily change its shape (Fig. 14).
Liquids easily change their shape but retain their volume.
The air we breathe is a gaseous substance, or gas. Since most gases are colorless and transparent, they are invisible.
The presence of air can be felt when standing at the open window of a moving train. Its presence in the surrounding space can be felt if there is a draft in the room, and can also be proven using simple experiments.
If you turn a glass upside down and try to lower it into water, the water will not enter the glass because it is filled with air. Now let’s lower a funnel into the water, which is connected by a rubber hose to a glass tube (Fig. 15). The air from the funnel will begin to escape through this tube.
These and many other examples and experiments confirm that there is air in the surrounding space.
Gases, unlike liquids, easily change their volume. When we squeeze a tennis ball, we change the volume of air filling the ball. A gas placed in a closed container occupies the entire container. You cannot fill half a bottle with gas the way you can with liquid.
Gases do not have their own shape and constant volume. They take the shape of the vessel and completely fill the volume provided to them.
- What three states of matter do you know? 2. List the properties of solids. 3. Name the properties of liquids. 4. What properties do gases have?
Water and gas. They all differ in their properties. Liquids occupy a special place in this list. Unlike solids, liquids do not have molecules arranged in an orderly manner. Liquid is a special state of matter, intermediate between gas and solid. Substances in this form can only exist if certain temperature ranges are strictly observed. Below this interval, the liquid body will turn into a solid, and above - into a gaseous one. In this case, the boundaries of the interval directly depend on pressure.
Water
One of the main examples of a liquid body is water. Despite belonging to this category, water can take the form of a solid or gas - depending on the temperature environment. During the transition from a liquid to a solid state, the molecules of an ordinary substance are compressed. But water behaves completely differently. When it freezes, its density decreases, and instead of sinking, the ice floats to the surface. Water in its ordinary, fluid state has all the properties of a liquid - it always has a specific volume, however, there is no specific shape.
Therefore, water always retains heat under the surface of ice. Even if the ambient temperature is -50°C, under the ice it will still be around zero. However, in elementary school you don’t have to delve into the details of the properties of water or other substances. In grade 3, the simplest examples of liquid bodies can be given - and it is advisable to include water in this list. After all, the student primary school must have a general understanding of the properties of the surrounding world. At this stage it is enough to know that water in its normal state is a liquid.
Surface tension is a property of water
Water has a higher surface tension than other liquids. Thanks to this property, raindrops are formed, and, consequently, the water cycle in nature is maintained. Otherwise, water vapor could not so easily turn into drops and spill onto the surface of the earth in the form of rain. Water, indeed, is an example of a liquid body, on which the possibility of the existence of living organisms on our planet directly depends.
Surface tension is caused by the molecules of a liquid being attracted to each other. Each particle tends to surround itself with others and leave the surface of the liquid body. That is why soap bubbles and bubbles formed during boiling water tend to take a liquid form - with this volume, only a ball can have a minimum surface thickness.
Liquid metals
However, not only the substances familiar to humans, with which he deals in everyday life, belong to the class of liquid bodies. Among this category there are many various elements periodic table Mendeleev. An example of a liquid body is also mercury. This substance is widely used in the manufacture of electrical devices, metallurgy, chemical industry.
Mercury is a liquid, shiny metal that evaporates when room temperature. It is capable of dissolving silver, gold and zinc, thereby forming amalgams. Mercury is an example of what kinds of liquid bodies are classified as dangerous to human life. Its vapors are toxic and hazardous to health. The damaging effect of mercury usually appears some time after exposure to poisoning.
A metal called cesium is also a liquid. Already at room temperature it is in semi-liquid form. Cesium appears to be a golden-white substance. This metal is slightly similar in color to gold, however, it is lighter.
Sulfuric acid
Almost all inorganic acids are also an example of what kind of liquid bodies there are. Eg, sulfuric acid, which appears to be a heavy oily liquid. It has neither color nor smell. When heated, it becomes a very strong oxidizing agent. In the cold, it does not interact with metals - for example, iron and aluminum. This substance exhibits its characteristics only in pure form. Dilute sulfuric acid does not exhibit oxidizing properties.
Properties
What liquid bodies exist besides those listed? This is blood, oil, milk, mineral oil, alcohol. Their properties allow these substances to easily take the form of containers. Like other liquids, these substances do not lose their volume if they are poured from one vessel to another. What other properties are inherent in each of the substances in this state? Liquid bodies and their properties are well studied by physicists. Let's look at their main characteristics.
Fluidity
One of main characteristics of any body in this category is fluidity. This term refers to the body's ability to accept different shape, even if it is subject to relatively weak external influence. It is thanks to this property that each liquid can flow in streams, splash onto the surrounding surface in drops. If bodies of this category did not have fluidity, it would be impossible to pour water from a bottle into a glass.
Moreover, this property is expressed in different substances to varying degrees. For example, honey changes shape very slowly compared to water. This characteristic is called viscosity. This property depends on internal structure liquid body. For example, honey molecules are more like tree branches, while water molecules are more like balls with small bulges. When the liquid moves, honey particles seem to “cling to each other” - it is this process that gives it greater viscosity than other types of liquids.
Saving the form
We must also remember that no matter what example of liquid bodies we are talking about, they only change their shape, but do not change their volume. If you pour water into a beaker and pour it into another container, this characteristic will not change, although the body itself will take the shape of the new vessel into which it was just poured. The property of volume conservation is explained by the fact that both mutually attractive and repulsive forces act between molecules. It should be noted that liquids are almost impossible to compress through external influence due to the fact that they always take the shape of the container.
Liquid and solid bodies differ in that the latter do not obey. Let us recall that this rule describes the behavior of all liquids and gases, and lies in their property of transmitting the pressure exerted on them in all directions. However, it should be noted that those liquids that have lower viscosity do this faster than more viscous liquid bodies. For example, if you put pressure on water or alcohol, it will spread quite quickly.
Unlike these substances, pressure on honey or liquid oil will spread more slowly, however, just as evenly. In grade 3, examples of liquid bodies can be given without indicating their properties. Students will need more detailed knowledge in high school. However, if the student prepares additional material, this may help you get a higher grade in class.
Class 2 dangerous goods include pure gases, mixtures of gases, mixtures of one or more gases with one or more other substances, as well as products containing such substances. Substances and products of class 2 are divided into compressed gas; liquefied gas; refrigerated liquefied gas; dissolved gas; aerosol sprays and small containers containing gas (gas cartridges); other products containing gas under pressure; non-pressurized gases subject to special requirements (gas samples). Transporting Class 2 dangerous goods involves the risk of explosion, fire, suffocation, frostbite or poisoning.
Air- a natural mixture of gases consisting by volume of 78% nitrogen, 21% oxygen, 0.93% argon, 0.3% carbon dioxide and very small quantity noble gases, hydrogen, ozone, carbon monoxide, ammonia, methane, sulfur dioxide and others. Density of liquid air 0.96 g/cubic. cm (at -192°C and normal pressure). Air is necessary for many processes to occur: combustion of fuel, smelting of metals from ores, industrial production of various chemical compounds. Air is also used to produce oxygen, nitrogen and noble gases; as a refrigerant, heat and soundproofing material, working fluid in electrical insulating devices, pneumatic tires, jet and spray apparatus, pneumatic machines, etc.
Oxygen - chemical element, which has pronounced oxidizing properties. Oxygen is mainly used in medicine. In addition to medicine, oxygen is used in metallurgy and other industries, and liquid oxygen serves as an oxidizer for rocket fuel.
Propane– a colorless, flammable, odorless, explosive gas contained in natural and associated petroleum gases, in gases obtained from CO and H2, as well as during oil refining. Propane has a negative effect on the central nervous system; if liquid propane comes into contact with the skin, frostbite can occur.
Nitrogen- colorless gas, tasteless and odorless. Nitrogen is used in many industries: as an inert medium in various chemical and metallurgical processes, for filling free space in mercury thermometers, when pumping flammable liquids, etc. Liquid nitrogen is used in various refrigeration units. Nitrogen is used for industrial production ammonia, which is then processed into nitric acid, fertilizers, explosives, etc.
Chlorine- poisonous gas of yellow-green color. The main quantities of chlorine are processed at the site of its production into chlorine-containing compounds. Chlorine is also used for bleaching cellulose and fabrics, for sanitary needs and chlorinating water, as well as for chlorinating some ores to extract titanium, niobium, zirconium, etc. Chlorine poisoning is possible in the chemical, pulp and paper, textile, pharmaceutical industries, etc. d. Chlorine irritates the mucous membranes of the eyes and respiratory tract; often, a secondary infection joins the primary inflammatory changes. The concentration of chlorine in the air is 500 mg/m3. m. with fifteen minutes of exposure is fatal. In order to prevent poisoning, it is necessary: sealing production equipment, efficient ventilation, if necessary, use a gas mask.
Ammonia- colorless gas with a sharp characteristic odor. Ammonia is used to produce nitrogen fertilizers, explosives and polymers, nitric acid, soda and other chemical industry products. Liquid ammonia is used as a solvent. IN refrigeration technology ammonia is used as a refrigerant (717). Also widely used is a 10% ammonia solution ( ammonia) received in medicine. According to its physiological effect on the body, it belongs to the group of substances with asphyxiating and neurotropic effects, capable of causing toxic pulmonary edema and severe damage if inhaled. nervous system. Ammonia has both local and resorptive effects. Ammonia vapors strongly irritate the mucous membranes of the eyes and respiratory organs, as well as skin, cause excessive lacrimation, pain in the eyes, chemical burns of the conjunctiva and cornea, loss of vision, coughing attacks, redness and itching of the skin. When liquefied ammonia and its solutions come into contact with the skin, a burning sensation occurs, and a chemical burn with blisters and ulcerations is possible. In addition, liquefied ammonia absorbs heat when it evaporates, and when it comes into contact with the skin, frostbite of varying degrees occurs.
Gaseous state of matter
Polymers are of natural (plant and animal tissues) and artificial (plastics, cellulose, fiberglass, etc.) origin.
Just as in the case of ordinary molecules, a system of macromolecules. forming a polymer tends to the most probable state - a stable equilibrium corresponding to a minimum free energy. Therefore, in principle, polymers should also have a crystal lattice structure. However, due to the bulk and complexity of macromolecules, only in a few cases it was possible to obtain perfect macromolecular crystals. In most cases, polymers consist of crystalline and amorphous regions.
Liquid state characterized by the fact that the potential energy of attraction of molecules slightly exceeds their kinetic energy in absolute value. The force of attraction between molecules in a liquid ensures that the molecules are held in the volume of the liquid. At the same time, the molecules in a liquid are not connected to each other by stationary stable bonds, as in crystals. They densely fill the space occupied by the liquid, so liquids are practically incompressible and have sufficient high density. Groups of molecules can change their relative position, which ensures the fluidity of liquids. The property of a liquid to resist flow is called viscosity. Liquids are characterized by diffusion and Brownian motion, but to a much lesser extent than gases.
The volume occupied by a liquid is limited by the surface. Since, for a given volume, a sphere has the minimum surface area, the liquid in a free state (for example, in weightlessness) takes the shape of a sphere.
Liquids have some structure, which, however, is much less pronounced than that of solids. The most important property of liquids is isotropy of properties. Simple perfect model liquid has not yet been created.
There is an intermediate state between liquids and crystals, which is called liquid crystalline. A feature of liquid crystals from a molecular point of view is the elongated, spindle-shaped shape of their molecules, which leads to anisotropy of their properties.
There are two types of liquid crystals - nematics and smectics. Smectics are characterized by the presence of parallel layers of molecules that differ from each other in the order of their structure. In nematics, order is ensured by the orientation of molecules. The anisotropy of the properties of liquid crystals determines their important optical properties. Liquid crystals can, for example, be transparent in one direction and opaque in another. It is important that the orientation of liquid crystal molecules and their layers can be easily controlled using external influences(eg temperature, electric and magnetic fields).
Gaseous state of matter occurs when
The kinetic energy of the thermal motion of molecules exceeds the potential energy of their binding. The molecules tend to move away from each other. The gas has no structure, occupies the entire volume provided to it, and is easily compressed; Diffusion occurs easily in gases.
The properties of substances in a gaseous state are explained by the kinetic gas theory. Its main postulates are as follows:
All gases are made up of molecules;
The sizes of molecules are negligible compared to the distances between them;
Molecules are constantly in a state of chaotic (Brownian) motion;
Between collisions, the molecules maintain a constant speed of motion; trajectories between collisions are straight line segments;
The collision between molecules and molecules with the walls of the vessel are ideally elastic, i.e. the total kinetic energy of the colliding molecules remains unchanged.
Let us consider a simplified model of a gas that obeys the above postulates. Such a gas is called an ideal gas. Let an ideal gas consist of N identical molecules, each of which has a mass m, is in a cubic vessel with an edge length l(Fig. 5.14). Molecules move chaotically; their average speed<v>. To simplify, let us divide all the molecules into three equal groups and assume that they move only in directions perpendicular to the two opposite walls of the vessel (Fig. 5.15).
Rice. 5.14.
Each gas molecule moving at a speed<v> in case of an absolutely elastic collision with the wall of the vessel, it will change the direction of movement to the opposite without changing the speed. Molecular Momentum<R> = m<v> becomes equal to - m<v>. The change in momentum in each collision is obviously . The force acting during this collision is equal to F= -2m<v>/Δ t. Complete change in momentum upon collision with the walls of all N/3 molecules equals 
. Let's define the time interval Δ t, during which all N/3 collisions will occur: D t = 2//< v >. Then the average value of the force acting on any wall is
Pressure R define the gas on the wall as the force ratio<F> to the wall area l 2:
Where V = l 3 – volume of the vessel.
Thus, the pressure of a gas is inversely proportional to its volume (recall that this law was empirically established by Boyle and Marriott).
Let us rewrite expression (5.4) in the form
Here is the average kinetic energy of gas molecules. it is proportional to absolute temperature T:
Where k– Boltzmann constant.
Substituting (5.6) into (5.5), we obtain
It is convenient to go from the number of molecules N to the number of moles n gas, we recall that ( N A is Avogadro’s number), and then
Where R = kN A - is the universal gas constant.
Expression (5.8) is the equation of state of a classical ideal gas for n moles. This equation, written for an arbitrary mass m gas
Where M - molar mass gas is called the Clapeyron-Mendeleev equation (see (5.3)).
Real gases obey this equation to a limited extent. The fact is that equations (5.8) and (5.9) do not take into account the intermolecular interaction in real gases - van der Waals forces.
Phase transitions. A substance, depending on the conditions in which it is located, can change its state of aggregation, or, as they say, move from one phase to another. This transition is called a phase transition.
As stated above, the most important factor, which determines the state of a substance is its temperature T, characterizing the average kinetic energy of thermal motion of molecules and pressure R. Therefore, states of matter and phase transitions are analyzed using a state diagram, where the values are plotted along the axes T And R, and each point on the coordinate plane determines the state of a given substance corresponding to these parameters. Let's analyze a typical diagram (Fig. 5.16). Curves OA, AB, AK separate states of matter. When enough low temperatures Almost all substances are in a solid crystalline state.
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The diagram highlights two characteristic points: A And TO. Dot A called triple point; at appropriate temperatures ( T t) and pressure ( R r) it contains gas, liquid and solid in equilibrium at the same time.
Dot TO indicates a critical condition. At this point (at T cr and R cr) the difference between liquid and gas disappears, i.e. the latter have the same physical properties.
Curve OA is a sublimation (sublimation) curve; at appropriate pressure and temperature, a gas-solid transition (solid-gas) occurs, bypassing the liquid state.
Under pressure R T< R < R The transition from the gaseous to the solid state (and vice versa) can only occur through the liquid phase.
Curve AK corresponds to evaporation (condensation). At appropriate pressure and temperature, the transition “liquid – gas” (and vice versa) occurs.
Curve AB is the liquid-solid transition curve (melting and crystallization). This curve has no end, since the liquid state always differs from the crystalline state in structure.
To illustrate, we present the shape of the surfaces of states of matter in variables p, v, t(Fig. 5.17), where V- volume of substance
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The letters G, F, T indicate areas of surfaces whose points correspond to gaseous, liquid or solid states, and areas surfaces T-G, Zh-T, T-Zh - two-phase states. Obviously, if we project the dividing lines between the phases onto the coordinate plane RT, we obtain phase diagram(see Fig. 5.16).
Quantum liquid - helium. At ordinary temperatures in macroscopic bodies, due to pronounced chaotic thermal motion, quantum effects are imperceptible. However, with decreasing temperature, these effects can come to the fore and manifest themselves macroscopically. For example, crystals are characterized by the presence of thermal vibrations of ions located at the nodes of the crystal lattice. As the temperature decreases, the amplitude of the oscillations decreases, but even when approaching absolute zero, the oscillations, contrary to classical ideas, do not stop.
The explanation for this effect follows from the uncertainty relation. A decrease in the amplitude of oscillations means a decrease in the localization area of the particle, i.e., the uncertainty of its coordinates. According to the uncertainty relation, this leads to an increase in the uncertainty of the momentum. Thus, the “stopping” of a particle is prohibited by the laws of quantum mechanics.
This purely quantum effect manifests itself in the existence of matter remaining in liquid state even at temperatures close to absolute zero. Such a “quantum” liquid is helium. The energy of zero-point oscillations is enough to destroy crystal lattice. However, at a pressure of about 2.5 MPa, liquid helium still crystallizes.
Plasma. The imparting of significant energy to the atoms (molecules) of a gas from the outside leads to ionization, i.e., the disintegration of atoms into ions and free electrons. This state of matter is called plasma.
Ionization occurs, for example, when a gas is strongly heated, which leads to a significant increase in the kinetic energy of atoms, during an electrical discharge in the gas (impact ionization by charged particles), or when the gas is exposed to electromagnetic radiation (autoionization). Plasma obtained at ultra-high temperatures is called high-temperature.
Since ions and electrons in plasma carry uncompensated electric charges, their mutual influence is significant. Between charged plasma particles there is not a pair interaction (as in a gas), but a collective interaction. Due to this, plasma behaves as a kind of elastic medium in which various oscillations and waves are easily excited and propagated
Plasma actively interacts with electric and magnetic fields. Plasma is the most common state of matter in the Universe. Stars consist of high-temperature plasma, cold nebulae - of low-temperature plasma. Weakly ionized low-temperature plasma exists in the Earth's ionosphere.
References for Chapter 5
1. Akhiezer A. I., Rekalo Ya. P. Elementary particles. - M.: Nauka, 1986.
2. Azshlov A. The world of carbon. - M.: Chemistry, 1978.
3. Bronshtein M.P. Atoms and electrons. - M.: Nauka, 1980.
4. Benilovsky V. D. These amazing liquid crystals. - M: Enlightenment, 1987.
5. Vlasov N. A. Antimatter. - M.: Atomizdat, 1966.
6. Christie R., Pitti A. Structure of matter: an introduction to modern physics. - M.: Nauka, 1969.
7. Krejci V. The world through the eyes of modern physics. - M.: Mkr, 1984.
8. Nambu E. Quarks. - M.: Mir, 1984.
9. Okun L. B. α, β, γ, …,: an elementary introduction to the physics of elementary particles. - M.: Nauka, 1985.
10. Petrov Yu. I. Physics of small particles. - M.: Nauka, 1982.
11. I, Purmal A.P. et al. How substances are converted. - M.: Nauka, 1984.
12. Rosenthal I.M. Elementary particles and the structure of the universe. - M.: Nauka, 1984.
13. Smorodinsky Ya. A. Elementary particles. - M.: Knowledge, 1968.
H2O - water, Liquid metal - mercury! The liquid state is usually considered intermediate between a solid and a gas: a gas retains neither volume nor shape, but a solid retains both.
The shape of liquid bodies can be determined entirely or partly by the fact that their surface behaves like an elastic membrane. So, water can collect in drops. But liquid is capable of flowing even under its stationary surface, and this also means non-preservation of shape ( internal parts liquid body).
Liquid molecules do not have a definite position, but at the same time they do not have complete freedom of movement. There is an attraction between them, strong enough to keep them close.
A substance in a liquid state exists in a certain temperature range, below which it turns into a solid state (crystallization occurs or transformation into a solid-state amorphous state - glass), above which it turns into a gaseous state (evaporation occurs). The boundaries of this interval depend on pressure.
As a rule, a substance in the liquid state has only one modification. (The most important exceptions are quantum liquids and liquid crystals.) Therefore, in most cases, a liquid is not only a state of aggregation, but also a thermodynamic phase (liquid phase).
All liquids are usually divided into pure liquids and mixtures. Some liquid mixtures have great importance for life: blood, sea water etc. Liquids can act as solvents.
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Physical properties of liquids
Fluidity
The main property of liquids is fluidity. If you apply to a section of liquid that is in equilibrium external force, then a flow of liquid particles arises in the direction in which this force is applied: the liquid flows. Thus, under the influence of unbalanced external forces, the liquid does not retain its shape and relative arrangement of parts, and therefore takes the shape of the vessel in which it is located.
Unlike plastic solids, the liquid has no yield limit: it is enough to apply an arbitrarily small external force for the liquid to flow.
Volume conservation
One of characteristic properties liquid is that it has a certain volume (under constant external conditions). Liquids are extremely difficult to compress mechanically because, unlike gases, there is very little free space between the molecules. The pressure exerted on a liquid enclosed in a vessel is transmitted without change to each point in the volume of this liquid (Pascal’s law is also valid for gases). This feature, along with very low compressibility, is used in hydraulic machines.
Liquids generally increase in volume (expand) when heated and decrease in volume (contract) when cooled. However, there are exceptions, for example, water contracts when heated, at normal pressure and at temperatures from 0 °C to approximately 4 °C.
Viscosity
In addition, liquids (like gases) are characterized by viscosity. It is defined as the ability to resist the movement of one part relative to another - that is, as internal friction.
When adjacent layers of liquid move relative to each other, collisions of molecules inevitably occur in addition to that caused by thermal motion. Forces arise that inhibit orderly movement. In this case, the kinetic energy of ordered movement turns into thermal energy - the energy of chaotic movement of molecules.
The liquid in the vessel, set in motion and left to its own devices, will gradually stop, but its temperature will increase.
