Evaporation and evaporation of water. Evaporation of water

For example, from the surface of an open vessel, from the surface of a reservoir, etc. Evaporation occurs at any temperature, but for any liquid its speed increases with increasing temperature. The volume occupied by a given mass of substance increases abruptly during evaporation.

Clouds in the sky, frost on the trees - these are all consequences of the processes of water evaporation and condensation of water vapor.

Two main cases must be distinguished. The first is when evaporation occurs in a closed vessel and the temperature at all points of the vessel is the same. For example, water evaporates inside a steam boiler or in a kettle closed with a lid if the temperature of the water and steam is below the boiling point. In this case, the volume of steam generated is limited by the space of the vessel. The vapor pressure reaches a certain limiting value at which it is in thermal equilibrium with the liquid; such steam called rich, and its pressure is steam pressure. The second case is when the space above the liquid is not closed; This is how water evaporates from the surface of the pond. In this case, equilibrium is almost never achieved, and the steam is unsaturated, and the rate of evaporation depends on many factors.

A measure of the rate of evaporation is the amount of substance escaping per unit time from a unit of free surface of the liquid. English physicist and chemist D. Dalton at the beginning of the 19th century. found that the rate of evaporation is proportional to the difference between the pressure of saturated vapor at the temperature of the evaporating liquid and the actual pressure of the real vapor that exists above the liquid. If liquid and vapor are in equilibrium, then the evaporation rate is zero. More precisely, it happens, but the reverse process also occurs at the same speed - condensation(transition of a substance from a gaseous or vaporous state to a liquid). The rate of evaporation also depends on whether it occurs in a calm or moving atmosphere; its speed increases if the resulting vapor is blown off by an air stream or pumped out by a pump.

If evaporation occurs from a liquid solution, then different substances evaporate at different rates. The rate of evaporation of a given substance decreases with increasing pressure of extraneous gases, such as air. Therefore, evaporation into emptiness occurs at the highest speed. On the contrary, by adding a foreign, inert gas to the vessel, evaporation can be greatly slowed down.

During evaporation, molecules escaping from a liquid must overcome the attraction of neighboring molecules and do work against the surface tension forces holding them in the surface layer. Therefore, for evaporation to occur, heat must be imparted to the evaporating substance, drawing it from the internal energy reserve of the liquid itself or taking it from surrounding bodies. The amount of heat that must be imparted to a liquid at a given temperature and a fixed pressure in order to convert it into vapor at the same temperature and pressure is called heat of vaporization. The vapor pressure increases with increasing temperature, the more strongly the higher the heat of evaporation.

If heat is not supplied from the outside to the evaporating liquid or it is not supplied sufficiently, then the liquid cools. That is why, leaving a wet hand in the air, we feel cold. By forcing a liquid placed in a vessel with non-heat-conducting walls to evaporate intensely, it can be significantly cooled. According to kinetic theory, the fastest molecules evaporate, the average energy of the molecules remaining in the liquid decreases - this is why the liquid cools.

Sometimes also called evaporation sublimation, or sublimation, i.e., the transition of a solid into a gaseous state. Almost all of their patterns are really similar. The heat of sublimation is greater than the heat of evaporation by approximately the heat of fusion.

At temperatures below the melting point, the saturated vapor pressure of most solids is very low, and their evaporation is practically absent. There are, however, exceptions. Thus, water at 0 °C has a saturated vapor pressure of 4.58 mm Hg. Art., and ice at −1 °C - 4.22 mm Hg. Art. and even at −10 °C - still 1.98 mmHg. Art. These relatively large water vapor pressures explain the easily observed evaporation of solid ice, in particular the well-known fact of wet laundry drying in the cold.

If you leave a container of water uncovered, the water will evaporate after a while. If you do the same experiment with ethyl alcohol or gasoline, the process occurs somewhat faster. If you heat a pot of water on a sufficiently powerful burner, the water will boil.

All these phenomena are a special case of vaporization, the transformation of liquid into vapor. There are two types of vaporization evaporation and boiling.

What is evaporation

Evaporation is the formation of vapor from the surface of a liquid. Evaporation can be explained as follows.

During collisions, the speeds of molecules change. Often there are molecules whose speed is so high that they overcome the attraction of neighboring molecules and break away from the surface of the liquid. (Molecular structure of matter). Since even in a small volume of liquid there are a lot of molecules, such cases occur quite often, and there is a constant process of evaporation.

Molecules separated from the surface of the liquid form steam above it. Some of them, due to chaotic movement, return back to the liquid. Therefore, evaporation occurs faster if there is wind, since it carries the vapor away from the liquid (here the phenomenon of “capture” and separation of molecules from the surface of the liquid by the wind also takes place).

Therefore, in a closed vessel, evaporation quickly stops: the number of molecules that “come off” per unit time becomes equal to the number that “returned” to the liquid.

Evaporation rate depends on the type of liquid: the less attraction between the molecules of the liquid, the more intense the evaporation.

The larger the surface area of a liquid, the more molecules have the opportunity to leave it. This means that the intensity of evaporation depends on the surface area of the liquid.

As the temperature increases, the speeds of the molecules increase. Therefore, the higher the temperature, the more intense the evaporation.

What is boiling

Boiling is intense vaporization that occurs as a result of heating a liquid, the formation of steam bubbles in it, floating to the surface and bursting there.

During boiling, the temperature of the liquid remains constant.

Boiling point is the temperature at which a liquid boils. Usually, when talking about the boiling point of a given liquid, we mean the temperature at which this liquid boils at normal atmospheric pressure.

During vaporization, the molecules that are separated from the liquid take away some of the internal energy from it. Therefore, as the liquid evaporates, it cools.

Specific heat of vaporization

A physical quantity characterizing the amount of heat required to evaporate a unit mass of a substance is called specific heat of vaporization. (follow the link for a more detailed analysis of this topic)

In the SI system, the unit of measurement for this quantity is J/kg. It is designated by the letter L.

Evaporation of a liquid occurs at any temperature and the faster the higher the temperature, the larger the free surface area of the evaporating liquid and the faster the vapors formed above the liquid are removed.

At a certain temperature, depending on the nature of the liquid and the pressure under which it is located, vaporization begins in the entire mass of the liquid. This process is called boiling.

This is a process of intense vaporization not only from the free surface, but also in the volume of the liquid. Bubbles filled with saturated steam form in the volume. They rise upward under the action of buoyant force and burst on the surface. The centers of their formation are tiny bubbles of foreign gases or particles of various impurities.

If the bubble has dimensions of the order of several millimeters or more, then the second term can be neglected and, therefore, for large bubbles at constant external pressure, the liquid boils when the saturated vapor pressure in the bubbles becomes equal to the external pressure.

As a result of chaotic movement above the surface of the liquid, the vapor molecule, falling into the sphere of action of molecular forces, returns to the liquid again. This process is called condensation.

Evaporation and boiling

Evaporation and boiling are two ways in which a liquid can change into a gas (steam). The process of such a transition is called vaporization. That is, evaporation and boiling are methods of vaporization. There are significant differences between these two methods.

Evaporation occurs only from the surface of the liquid. It is the result of the fact that the molecules of any liquid are constantly moving. Moreover, the speed of molecules is different. Molecules with sufficiently high speed, once on the surface, can overcome the force of attraction of other molecules and end up in the air. Water molecules, individually in the air, form steam. It is impossible to see the couples through their eyes. What we see as water fog is already the result of condensation (the process opposite to vaporization), when, when cooled, steam collects in the form of tiny droplets.

As a result of evaporation, the liquid itself cools as the fastest molecules leave it. As you know, temperature is precisely determined by the speed of movement of the molecules of a substance, that is, their kinetic energy.

The rate of evaporation depends on many factors. Firstly, it depends on the temperature of the liquid. The higher the temperature, the faster the evaporation. This is understandable, since the molecules move faster, which means it is easier for them to escape from the surface. The rate of evaporation depends on the substance. In some substances, the molecules are attracted more strongly, and therefore it is more difficult for them to fly out, while in others they are weaker, and therefore they leave the liquid more easily. Evaporation also depends on surface area, air saturation with steam, and wind.

The most important thing that distinguishes evaporation from boiling is that evaporation occurs at any temperature, and it occurs only from the surface of the liquid.

Unlike evaporation, boiling occurs only at a certain temperature. Each substance in a liquid state has its own boiling point. For example, water at normal atmospheric pressure boils at 100 °C, and alcohol at 78 °C. However, as atmospheric pressure decreases, the boiling point of all substances decreases slightly.

When water boils, air dissolved in it is released. Since the vessel is usually heated from below, the temperature in the lower layers of water is higher, and bubbles first form there. Water evaporates into these bubbles and they become saturated with water vapor.

Since the bubbles are lighter than the water itself, they rise upward. Due to the fact that the upper layers of water have not warmed up to the boiling point, the bubbles cool down and the steam in them condenses back into water, the bubbles become heavier and sink again.

When all layers of liquid are heated to boiling temperature, the bubbles no longer descend, but rise to the surface and burst. The steam from them ends up in the air. Thus, during boiling, the process of vaporization occurs not on the surface of the liquid, but throughout its entire thickness in the air bubbles that form. Unlike evaporation, boiling is possible only at a certain temperature.

It should be understood that when a liquid boils, normal evaporation from its surface also occurs.

What determines the rate of evaporation of liquid?

Sometimes evaporation is also called sublimation, or sublimation, i.e. the transition of a solid into a gaseous state. Almost all of their patterns are really similar. The heat of sublimation is greater than the heat of evaporation by approximately the heat of fusion.

So, the rate of evaporation depends on:

A kind of liquid. The liquid whose molecules attract each other with less force evaporates faster. Indeed, in this case, a larger number of molecules can overcome attraction and fly out of the liquid.
Evaporation occurs faster the higher the temperature of the liquid. The higher the temperature of a liquid, the greater the number of fast-moving molecules in it that can overcome the attractive forces of surrounding molecules and fly away from the surface of the liquid.
The rate of evaporation of a liquid depends on its surface area. This reason is explained by the fact that the liquid evaporates from the surface, and the larger the surface area of the liquid, the greater the number of molecules simultaneously flying from it into the air.
Evaporation of liquid occurs faster with wind. Simultaneously with the transition of molecules from liquid to vapor, the reverse process also occurs. Moving randomly over the surface of the liquid, some of the molecules that left it return to it again. Therefore, the mass of the liquid in a closed container does not change, although the liquid continues to evaporate.

conclusions

We say that water evaporates. But what does it mean? Evaporation is the process by which a liquid in air quickly becomes a gas or vapor. Many liquids evaporate very quickly, much faster than water. This applies to alcohol, gasoline, and ammonia. Some liquids, such as mercury, evaporate very slowly.

What causes evaporation? To understand this, you need to understand something about the nature of matter. As far as we know, every substance is made up of molecules. Two forces act on these molecules. One of them is cohesion, which attracts them to each other. The other is the thermal movement of individual molecules, which causes them to fly apart.

If the adhesive force is higher, the substance remains in a solid state. If the thermal motion is so strong that it exceeds cohesion, then the substance becomes or is a gas. If the two forces are approximately balanced, then we have a liquid.

Water, of course, is a liquid. But on the surface of a liquid there are molecules that move so fast that they overcome the force of adhesion and fly away into space. The process of molecules leaving is called evaporation.

Why does water evaporate faster when it is exposed to the sun or warmed up? The higher the temperature, the more intense the thermal movement in the liquid. This means that more and more molecules gain enough speed to fly away. As the fastest molecules fly away, the speed of the remaining molecules slows down on average. Why does the remaining liquid cool through evaporation?

So when water dries up, it means it has turned into gas or vapor and become part of the air.

student of 9B class Chernyshova Kristina MBOU Secondary School No. 27 in Stavropol.

The topic of this research work is to study the dependence of the evaporation rate on various external conditions. This problem remains relevant in various technological fields and in the nature around us. Suffice it to say that the water cycle in nature occurs through the phases of evaporation and volumetric condensation. The water cycle, in turn, determines such important phenomena as solar influence on the planet or simply the normal existence of living beings in general.

Hypothesis: the rate of evaporation depends on the type of substance, the surface area of the liquid and air temperature, the presence of moving air currents above its surface.

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MUNICIPAL BUDGETARY EDUCATIONAL INSTITUTION

SECONDARY SCHOOL No. 27

Research work:

“Evaporation and factors influencing this process”

Completed by: 9B grade student

Chernyshova Kristina.

Teacher: Vetrova L.I.

Stavropol

2013

I.Introduction…………………………………………………………………………………....…….3

II Theoretical part……………………………………………………….4

1. Basic principles of molecular kinetic theory…………………4

2. Temperature………………………………………………………..………...6

3. Characteristics of the liquid state of a substance…………………………….....7

4. Internal energy…………………………………………………….……..8

5. Evaporation………………………………………………………………………………..10

III.Research part……………………………..…………………..14

IV.Conclusion……………………………………………………………………………….…..21

V. Literature……………………………………………………………………………….22

Introduction

Evaporation is widely used in industrial practice for purifying substances, drying materials, separating liquid mixtures, and air conditioning. Evaporative water cooling is used in circulating water supply systems of enterprises.

In carburetor and diesel engines, the size distribution of fuel particles determines their combustion rate, and hence the process of engine operation. Condensation mists not only form water vapor during the combustion of various fuels, but many condensation nuclei are formed, which can serve as condensation centers for other vapors. These complex processes determine the efficiency of engines and fuel loss. Achieving the best results in the study of these phenomena could serve as information for the movement of technical progress in our country.

So , the purpose of this work- explore the dependence of the evaporation rate on various environmental factors and, using graphs and careful observations, notice patterns.

Hypothesis : the rate of evaporation depends on the type of substance, the surface area of the liquid and air temperature, the presence of moving air currents above its surface.

When conducting the research, we used various simple instruments, such as a thermometer, as well as Internet resources and other literature.

II Theoretical part.

1. Basic principles of molecular kinetic theory

The properties of substances found in nature and technology are diverse and varied: glass is transparent and fragile, and steel is elastic and opaque, copper and silver are good conductors of heat and electricity, but porcelain and silk are bad, etc.

What is the internal structure of any substance? Is it solid (continuous) or has a granular (discrete) structure, similar to the structure of a pile of sand?

The question of the structure of matter was posed back in Ancient Greece, but the lack of experimental data made its solution impossible, and for a long time (over two thousand years) it was not possible to verify the brilliant guesses about the structure of matter expressed by the ancient Greek thinkers Leucippus and Democritus (460-370 BC). AD), who taught that everything in nature consists of atoms in continuous motion. Their teaching was subsequently forgotten, and in the Middle Ages, matter was already considered continuous, and changes and states of bodies were explained with the help of weightless liquids, each of which personified a certain property of matter and could both enter and leave the body. For example, it was believed that adding caloric to a body causes it to heat up; on the contrary, cooling of the body occurs due to the flow of caloric, etc.

In the middle of the 17th century. French scientist P. Gassendi (1592-1655) returned to the views of Democritus. He believed that there are substances in nature that cannot be broken down into simpler components. Such substances are now called chemical elements, for example hydrogen, oxygen, copper, etc. According to Gassendi, each element consists of atoms of a certain type.

There are relatively few different elements in nature, but their atoms, combining into groups (among them there may be identical atoms), give the smallest particle of a new type of substance - a molecule. Depending on the number and type of atoms in a molecule, substances with various properties are obtained.

In the 18th century The works of M.V. Lomonosov appeared, laying the foundations of the molecular kinetic theory of the structure of matter. Lomonosov decisively fought for the expulsion from physics of weightless liquids like caloric, as well as atoms of cold, smell, etc., which were widely used at that time to explain the corresponding phenomena. Lomonosov proved that all phenomena are naturally explained by the movement and interaction of molecules of matter. - |At the beginning of the 19th century, the English scientist D. Dalton (1766-1844) showed that, using only ideas about atoms and molecules, it is possible to derive and explain chemical laws known from experiments. Thus, he scientifically substantiated the molecular structure of matter. After Dalton's work, the existence of atoms and molecules was recognized by the vast majority of scientists.

By the beginning of the 20th century. the sizes, masses and speeds of movement of molecules of matter were measured, the location of individual atoms in molecules was determined, in a word, the construction of a molecular kinetic theory of the structure of matter was finally completed, the conclusions of which were confirmed by many experiments.

The main provisions of this theory are as follows:

1) every substance consists of molecules between which there are intermolecular spaces;

2) molecules are always in continuous disorderly (chaotic) motion;

3) both attractive and repulsive forces act between molecules. These forces depend on the distance between the molecules. They are significant only at very short distances and quickly decrease as the molecules move away from each other. The nature of these forces is electrical.

2. Temperature.

If all bodies consist of continuously and randomly moving molecules, then how will the change in the speed of movement of the molecules, i.e., their kinetic energy, manifest itself, and what sensations will these changes cause in a person? It turns out that the change in the average kinetic energy of the translational motion of molecules is associated with heating or cooling of bodies.

Often a person determines the heat of the body by touch, for example, by touching a heating radiator with his hand, we say: the radiator is cold, warm or hot. However, determining whether a body is hot by touch is often deceptive. When in winter a person touches a wooden and metal body with his hand, it seems to him that the metal object is colder than the wooden one, although in reality their heating is the same. Therefore, it is necessary to establish a value that would evaluate the body’s heating objectively, and to create a device for measuring it.

The quantity characterizing the degree of heating of a body is called temperature. A device for measuring temperature is called a thermometer. The action of the most common thermometers is based on the expansion of bodies when heated and compression when cooled. When two bodies with different temperatures come into contact, an exchange of energy occurs between the bodies. In this case, a more heated body (with a high temperature) loses energy, and a less heated one (with a low temperature) gains it. This exchange of energy between bodies leads to equalization of their temperatures and ends when the temperatures of the bodies become equal.

A person’s feeling of warmth occurs when he receives energy from surrounding bodies, that is, when their temperature is higher than the temperature of a person. The feeling of cold is associated with the release of energy by a person to surrounding bodies. In the above example, a metal body seems colder to a person than a wooden one, because energy is transferred to metal bodies from the hand faster than to wooden ones, and in the first case the temperature of the hand decreases faster.

3. Characteristics of the liquid state of a substance.

The liquid molecules oscillate around a randomly occurring equilibrium position for some time t, and then jump to a new position. The time during which the molecule oscillates around the equilibrium position is called the “settled life” time of the molecule. It depends on the type of liquid and its temperature. When the liquid is heated, the “settled life” time decreases.

If a sufficiently small volume is isolated in a liquid, then during the time of “settled life” the ordered arrangement of liquid molecules is preserved in it, i.e. there is a semblance of a crystal lattice of solids. However, if we consider the arrangement of liquid molecules relative to each other in a large volume of liquid, it turns out to be chaotic.

Therefore, we can say that in a liquid there is a “short-range order” in the arrangement of molecules. The ordered arrangement of liquid molecules in small volumes is called quasicrystalline (crystal-like). With short-term effects on the liquid, less than the time of “settled life”, a great similarity of the properties of the liquid with the properties of the solid is revealed. For example, when a small stone with a flat surface hits water sharply, the stone bounces off it, i.e. the liquid exhibits elastic properties. If a swimmer jumping from a tower hits the surface of the water with his whole body, he will be seriously injured, since under these conditions the liquid behaves like a solid body.

If the time of exposure to the liquid is longer than the “settled life” time of the molecules, then the fluidity of the liquid is detected. For example, a person freely enters water from the bank of a river, etc. The main features of a liquid state are the fluidity of the liquid and the conservation of volume. The fluidity of a liquid is closely related to the “settled life” time of its molecules. The shorter this time, the greater the mobility of the liquid molecules, i.e., the greater the fluidity of the liquid, and its properties are closer to those of a gas.

The higher the temperature of a liquid, the more its properties differ from the properties of a solid and become closer to the properties of dense gases. Thus, the liquid state of a substance is intermediate between the solid and gaseous state of the same substance.

4. Internal energy

Every body is a collection of a huge number of particles. Depending on the structure of the substance, these particles are molecules, atoms or ions. Each of these particles, in turn, has a rather complex structure. Thus, a molecule consists of two or more atoms, atoms consist of a nucleus and an electron shell; the nucleus consists of protons and neutrons, etc.

The particles that make up a body are in continuous motion; in addition, they interact with each other in a certain way.

The internal energy of a body is the sum of the kinetic energies of the particles of which it consists and the energies of their interaction with each other (potential energies).

Let's find out under what processes the internal energy of a body can change.

1. First of all, it is obvious that the internal energy of a body changes when it deforms. In fact, during deformation the distance between particles changes; consequently, the energy of interaction between them also changes. Only in an ideal gas, where the forces of interaction between particles are neglected, is the internal energy independent of pressure.

2. Internal energy changes during thermal processes. Thermal processes are processes associated with changes in both the temperature of a body and its state of aggregation - melting or solidification, evaporation or condensation. When the temperature changes, the kinetic energy of movement of its particles changes. However, it should be emphasized that at the same time

The potential energy of their interaction also changes (except for the case of a rarefied gas). Indeed, an increase or decrease in temperature is accompanied by a change in the distance between equilibrium positions at the nodes of the crystal lattice of a body, which we register as thermal expansion of bodies. Naturally, the energy of particle interaction changes in this case. The transition from one state of aggregation to another is the result of a change in the molecular structure of the body, which causes a change in both the energy of interaction of particles and the nature of their movement.

3. The internal energy of the body changes during chemical reactions. In fact, chemical reactions are processes of rearrangement of molecules, their disintegration into simpler parts or, conversely, the emergence of more complex molecules from simpler ones or from individual atoms (reactions of analysis and synthesis). In this case, the forces of interaction between atoms and, accordingly, the energies of their interaction change significantly. In addition, the nature of both the movement of molecules and the interaction between them changes, because the molecules of the newly emerged substance interact with each other differently than the molecules of the original substances.

4. Under certain conditions, the nuclei of atoms undergo transformations that are called nuclear reactions. Regardless of the mechanism of the processes occurring in this case (and they can be very different), they are all associated with a significant change in the energy of interacting particles. Consequently, nuclear reactions are accompanied by a change in the internal energy of the body that contains these nuclei

5. Evaporation

The transition of a substance from a liquid to a gaseous state is called vaporization, and the transition of a substance from a gaseous to a liquid state is called condensation.

One type of vapor formation is evaporation. Evaporation is the formation of vapor that occurs only from the free surface of a liquid bordering a gaseous medium. Let's find out how evaporation is explained based on the molecular kinetic theory.

Since the molecules of a liquid move randomly, among the molecules of its surface layer there will always be molecules that move in the direction from the liquid to the gaseous medium. However, not all such molecules will be able to fly out of the liquid, since they are subject to molecular forces that pull them back into the liquid. Therefore, only those of its molecules that have a sufficiently high kinetic energy will be able to escape beyond the surface layer of the liquid.

Indeed, when a molecule passes through a surface layer, it must do work against the molecular forces due to its kinetic energy. Those molecules whose kinetic energy is less than this work are drawn back into the liquid, and only those molecules whose kinetic energy is greater than this work are pulled out of the liquid. Molecules released from a liquid form vapor above its surface. Since molecules escaping from a liquid acquire kinetic energy as a result of collisions with other molecules of the liquid, the average speed of the chaotic movement of molecules inside the liquid should decrease during its evaporation. Thus, a certain energy must be expended to transform the liquid phase of a substance into a gaseous one. Vapor molecules located above the surface of the liquid, during their chaotic movement, can fly back into the liquid and return to it the energy that they carried away during evaporation. Consequently, during evaporation, condensation of vapor always occurs simultaneously, accompanied by an increase in the internal energy of the liquid.

What reasons influence the rate of evaporation of liquid?

1. If you pour equal volumes of water, alcohol and ether into identical saucers and observe their evaporation, it will turn out that the ether will evaporate first, then the alcohol, and the water will evaporate last. Therefore, the speed

evaporation depends on the type of liquid.

2. The larger its free surface, the faster the same liquid evaporates. For example, if the same volumes of water are poured into a saucer and into a glass, then the water will evaporate from the saucer faster than from the glass.

3. It is easy to notice that hot water evaporates faster than cold water.

The reason for this is clear. The higher the temperature of the liquid, the greater the average kinetic energy of its molecules and, therefore, the greater the number of them leaving the liquid in the same time.

4. In addition, the rate of evaporation of a liquid is greater, the lower the external pressure on the liquid and the lower the vapor density of this liquid above its surface.

For example, when there is wind, laundry dries faster than in calm weather, since the wind carries away water vapor and this helps reduce steam condensation on the laundry.

Since energy is expended on the evaporation of a liquid due to the energy of its molecules, the temperature of the liquid decreases during the evaporation process. This is why a hand soaked in ether or alcohol noticeably cools. This also explains the feeling of cold in a person when he comes out of the water after swimming on a hot, windy day.

If a liquid evaporates slowly, then, due to heat exchange with surrounding bodies, the loss of its energy is compensated by the influx of energy from the environment, and its temperature actually remains equal to the temperature of the environment. However, if the liquid evaporates at a high rate, its temperature may be significantly lower than the ambient temperature. With the help of "volatile" liquids, such as ether, a significant decrease in temperature can be achieved.

Let us also note that many solids, bypassing the liquid phase, can directly pass into the gaseous phase. This phenomenon is called sublimation, or sublimation. The odor of solids (for example, camphor, naphthalene) is explained by their sublimation (and diffusion). Sublimation is typical for ice, for example, laundry dries at temperatures below 0° G.

6. Hydrosphere and atmosphere of the Earth

1. The processes of evaporation and condensation of water play a decisive role in the formation of weather and climate conditions on our planet. On a global scale, these processes come down to the interaction of the hydrosphere and the Earth's atmosphere.

The hydrosphere consists of all the water available on our planet in all its states of aggregation; 94% of the hydrosphere falls on the World Ocean, the volume of which is estimated at 1.4 billion m3. It occupies 71% of the total area of the earth's surface, and if the solid surface of the earth were a smooth sphere, then water would cover it with a continuous layer 2.4 km deep; 5.4% of the hydrosphere is occupied by groundwater, as well as glaciers, atmospheric and soil moisture. And only 0.6% comes from fresh water from rivers, lakes and artificial reservoirs. From this it is clear how important it is to protect fresh water from pollution from industrial and transport waste.

2. The Earth’s atmosphere is usually divided into several layers, each of which has its own characteristics. The lower, surface layer of air is called the troposphere. Its upper limit in equatorial latitudes passes at an altitude of 16-18 km, and in polar latitudes - at an altitude of 10 km. The troposphere contains 90% of the mass of the entire atmosphere, which is 4.8 1018 kg. The temperature in the troposphere decreases with height. First, by 1 °C for every 100 m, and then, starting from an altitude of 5 km, the temperature drops to -70 °C.

Air pressure and density are continuously decreasing. The outermost layer of the atmosphere at an altitude of about 1000 km gradually passes into interplanetary space.

3. Research has shown that every day about 7·10 3 km 3 water and about the same amount falls as precipitation.

Carried away by rising air currents, water vapor rises, falling into the cold layers of the troposphere. As the vapor rises, it becomes saturated and then condenses to form raindrops and clouds.

During the process of steam condensation in the atmosphere, on average per day, an amount of heat is released 1.6 10 22 J, which is tens of thousands of times greater than the energy generated on planet Earth during the same time. This energy is absorbed by water as it evaporates. Thus, between the hydrosphere and the Earth’s atmosphere there is a continuous exchange of not only matter (water cycle), but also energy.

III. RESEARCH PART.

To study evaporation processes and determine the dependence of the evaporation rate on various conditions, a number of experiments were carried out.

Experiment 1. Study of the dependence of evaporation rate on air temperature.

Materials: Glass plates, 3% hydrogen peroxide solution, vegetable oil, alcohol, water, stopwatch, thermometer, refrigerator.

Progress of the experiment:Using a syringe, we apply substances to glass plates and observe the evaporation of the substances.

Alcohol Volume 0.5·10 -6 m 3

Air temperature: +24.

The result of the experiment: it took 3 hours for the liquid to completely evaporate;

Water. Volume 0.5·10 -6 m 3

Air temperature: +24.

The result of the experiment: it took 5 hours for the liquid to completely evaporate;

Hydrogen peroxide solution. Volume 0.5·10 -6 m 3

Air temperature: +24.

The result of the experiment: it took 8 hours for the liquid to completely evaporate;

Vegetable oil. Volume 0.5·10 -6 m 3

Air temperature: +24.

The result of the experiment: it took 40 hours for the liquid to completely evaporate;

We change the air temperature. Place the glasses in the refrigerator.

Alcohol. Volume 0.5·10 -6 m 3

Air temperature: +6.

The result of the experiment: it took 8 hours for the liquid to completely evaporate;

Water. Volume 0.5·10 -6 m 3

Air temperature: +6.

The result of the experiment: it took 10 hours for the liquid to completely evaporate;

Hydrogen peroxide solution. Volume 0.5·10 -6 m 3

Air temperature: +6.

The result of the experiment: it took 15 hours for the liquid to completely evaporate;

Vegetable oil. Volume 0.5·10 -6 m 3

Air temperature: +6

The result of the experiment: it took 72 hours for the liquid to completely evaporate;

Conclusion: The results of the study show that at different temperatures the amount of time required for the evaporation of the same substances is different. For the same liquid, the evaporation process occurs much faster at a higher temperature. This proves the dependence of the process under study on this physical parameter. As the temperature decreases, the duration of the evaporation process increases and vice versa.

Experiment 2 . Study of the dependence of the rate of evaporation on the surface area of the liquid.

Target: Investigate the dependence of the evaporation process on the surface area of the liquid.

Materials: Water, alcohol, watch, medical syringe, glass plates, ruler.

Progress of the experiment:We measure surface area using the formula: S=P·D 2 :4.

Using a syringe, we apply different liquids to the plate, shape it into a circle and observe the liquid until it completely evaporates. The air temperature in the room remains unchanged (+24)

Alcohol. Volume 0.5·10 -6 m 3

Surface area:0.00422m 2

The result of the experiment: it took 1 hour for the liquid to completely evaporate;

Water. Volume 0.5·10 -6 m 3

The result of the experiment: it took 2 hours for the liquid to completely evaporate;

Hydrogen peroxide solution. Volume 0.5·10 -6 m 3

Surface area: 0.00422 m 2

The result of the experiment: it took 4 hours for the liquid to completely evaporate;

Vegetable oil. Volume 0.5·10 -6 m 3

Surface area: 0.00422 m 2

The result of the experiment: it took 30 hours for the liquid to completely evaporate;

We change the conditions. We observe the evaporation of the same liquids at a different surface area.

Alcohol. Volume 0.5·10 -6 m 3

The result of the experiment: it took 3 hours for the liquid to completely evaporate;

Water. Volume 0.5·10 -6 m 3

Surface area: 0.00283 m 2

The result of the experiment: it took 4 hours for the liquid to completely evaporate;

Hydrogen peroxide solution. Volume 0.5·10 -6 m 3

The result of the experiment: it took 6 hours for the liquid to completely evaporate;

Vegetable oil. Volume 0.5·10 -6 m 3

Surface area 0.00283 m 2

The result of the experiment: it took 54 hours for the liquid to completely evaporate;

Conclusion: From the results of the study it follows that from vessels with different surface areas, evaporation occurs for different times. As can be seen from the measurements, this liquid evaporates faster from a vessel with a larger surface area, which proves the dependence of the process under study on this physical parameter. As the surface area decreases, the duration of the evaporation process increases and vice versa.

Experiment 3. Study of the dependence of the evaporation process on the type of substance.

Target: Investigate the dependence of the evaporation process on the type of liquid.

Devices and materials:Water, alcohol, vegetable oil, hydrogen peroxide solution, watch, medical syringe, glass plates.

Progress of the experiment.Using a syringe, we apply different types of liquid to the plates and monitor the process until it evaporates completely. The air temperature remains unchanged. The temperatures of the liquids are the same.

We obtain the results of studies of the difference between the evaporation of alcohol, water, 3% hydrogen peroxide solution, and vegetable oil from data from previous studies.

Conclusion: Different liquids require different amounts of time to completely evaporate. From the results it is clear that the evaporation process proceeds faster for alcohol and water, and slower for vegetable oil, that is, it serves as proof of the dependence of the evaporation process on the physical parameter - the type of substance.

Experiment 4. Study of the dependence of the rate of liquid evaporation on the speed of air masses.

Target: investigate the dependence of the rate of evaporation on wind speed.

Devices and materials:Water, alcohol, vegetable oil, hydrogen peroxide solution, watch, medical syringe, glass plates, hair dryer.

Progress. We create artificial movement of air masses using a hairdryer, observe the process, and wait until the liquid evaporates completely. The hair dryer has two modes: simple mode, turbo mode.

In case of simple mode:

Alcohol. Volume: 0.5·10 -6 m 3

Surface area: 0.00283 m 2 The result of the experiment: it took about 2 minutes for the liquid to completely evaporate;

Water. Volume 0.5·10 -6 m 3

Surface area: 0.00283 m 2

The result of the experiment: it took about 4 minutes for the liquid to completely evaporate;

Hydrogen peroxide solution. Volume: 0.5·10 -6 m 3

Surface area: 0.00283 m 2

The result of the experiment: it took about 7 minutes for the liquid to completely evaporate;

Vegetable oil. Volume: 0.5·10 -6 m 3

Surface area: 0.00283 m 2 The result of the experiment: it took about 10 minutes for the liquid to completely evaporate;

In case of turbo mode:

Alcohol. Volume: 0.5·10 -6 m 3

Surface area: 0.00283 m 2 The result of the experiment: it took about 1 minute for the liquid to completely evaporate;

Water. Volume: 0.5·10 -6 m 3

Surface area: 0.00283 m 2

The result of the experiment: it took about 3 minutes for the liquid to completely evaporate;

Hydrogen peroxide solution. Volume: 0.5·10 -6 m 3

Surface area: 0.00283 m 2 The result of the experiment: it took about 5 minutes for the liquid to completely evaporate;

Vegetable oil. Volume: 0.5·10 -6 m 3

Surface area: 0.00283 m 2

The result of the experiment: it took about 8 minutes for the liquid to completely evaporate;

Conclusion: The evaporation process depends on the speed of movement of air masses above the surface of the liquid. The higher the speed, the faster this process proceeds and vice versa.

So, studies have shown that the intensity of liquid evaporation varies for different liquids and increases with increasing temperature of the liquid, increasing its free surface area, and the presence of wind above its surface.

Conclusion.

As a result of the work, various sources of information on the issue of the evaporation process and the conditions for its occurrence were studied. The physical parameters that influence the rate of the evaporation process are determined. The dependence of the evaporation process on physical parameters was investigated, and the results obtained were analyzed. The stated hypothesis turned out to be correct. Theoretical assumptions were confirmed during the research process - the dependence of the rate of the evaporation process on physical parameters is as follows:

As the temperature of the liquid increases, the rate of the evaporation process increases and vice versa;

With a decrease in the free surface area of the liquid, the rate of the evaporation process decreases and vice versa;

The rate of the evaporation process depends on the type of liquid.

Thus, the process of evaporation of liquids depends on such physical parameters as temperature, free surface area and type of substance.

This work is of practical importance, since it investigated the dependence of the intensity of evaporation, a phenomenon that we encounter in everyday life, on physical parameters. Using this knowledge, you can control the progress of the process.

Literature

Pinsky A. A., Grakovsky G. Yu. Physics: Textbook for students of institutions

Secondary vocational education/Under general. Ed. Yu.I.Dika, N.S.Puryshevoy.-M.:FORUM:INFRA_M, 2002.-560 p.

Milkovskaya L.B. Let's repeat physics. Textbook for those entering universities. M., "Higher School", 1985.608 p.

Internet resources:http://ru.wikipedia.org/wiki/;

http://class-fizika.narod.ru/8_l 3.htm;

http://e-him.ru/?page=dynamic§ion=33&article=208 ;

Textbook on physics G.Ya. Myakishev "Thermodynamics"

Occurring from the free surface of a liquid.

Sublimation, or sublimation, i.e. The transition of a substance from a solid to a gaseous state is also called evaporation.

From everyday observations it is known that the amount of any liquid (gasoline, ether, water) located in an open vessel gradually decreases. The liquid does not disappear without a trace - it turns into steam. Evaporation is one of the types vaporization. Another type is boiling.

Evaporation mechanism.

How does evaporation occur? The molecules of any liquid are in continuous and random motion, and the higher the temperature of the liquid, the greater the kinetic energy of the molecules. The average value of kinetic energy has a certain value. But for each molecule the kinetic energy can be either greater or less than the average. If there is a molecule near the surface with kinetic energy sufficient to overcome the forces of intermolecular attraction, it will fly out of the liquid. The same thing will be repeated with another fast molecule, with the second, third, etc. Flying out, these molecules form vapor above the liquid. The formation of this steam is evaporation.

Energy absorption during evaporation.

As faster molecules fly out of the liquid during evaporation, the average kinetic energy of the molecules remaining in the liquid becomes less and less. This means that the internal energy of the evaporating liquid decreases. Therefore, if there is no influx of energy to the liquid from the outside, the temperature of the evaporating liquid decreases, the liquid cools (this is why, in particular, a person in wet clothes is colder than in dry ones, especially in the wind).

However, when water poured into a glass evaporates, we do not notice a decrease in its temperature. How can we explain this? The fact is that evaporation in this case occurs slowly, and the water temperature is maintained constant due to heat exchange with the surrounding air, from which the required amount of heat enters the liquid. This means that in order for the evaporation of a liquid to occur without changing its temperature, energy must be imparted to the liquid.

The amount of heat that must be imparted to a liquid to form a unit mass of vapor at a constant temperature is called heat of vaporization.

Liquid evaporation rate.

Unlike boiling, evaporation occurs at any temperature, however, as the temperature of the liquid increases, the evaporation rate increases. The higher the temperature of the liquid, the more fast-moving molecules have sufficient kinetic energy to overcome the attractive forces of neighboring particles and fly out of the liquid, and the faster evaporation occurs.

The rate of evaporation depends on the type of liquid. Volatile liquids whose intermolecular interaction forces are small (for example, ether, alcohol, gasoline) evaporate quickly. If you drop such a liquid on your hand, you will feel cold. Evaporating from the surface of the hand, such a liquid will cool and take away some heat from it.

The rate of evaporation of a liquid depends on its free surface area. This is explained by the fact that the liquid evaporates from the surface, and the larger the free surface area of the liquid, the greater the number of molecules simultaneously flies into the air.

In an open vessel, the mass of liquid gradually decreases due to evaporation. This is due to the fact that most of the vapor molecules disperse into the air without returning to the liquid (unlike what happens in a closed vessel). But a small part of them returns to the liquid, thereby slowing down evaporation. Therefore, with the wind, which carries away vapor molecules, the evaporation of the liquid occurs faster.

Application of evaporation in technology.

Evaporation plays an important role in energy, refrigeration, drying processes, and evaporative cooling. For example, in space technology, descent vehicles are coated with rapidly evaporating substances. When passing through the planet's atmosphere, the body of the device heats up as a result of friction, and the substance covering it begins to evaporate. Evaporating, it cools the spacecraft, thereby saving it from overheating.

Condensation.

Condensation(from lat. condensatio- compaction, condensation) - the transition of a substance from a gaseous state (vapor) to a liquid or solid state.

It is known that in the presence of wind, liquid evaporates faster. Why? The fact is that simultaneously with evaporation from the surface of the liquid, condensation occurs. Condensation occurs due to the fact that some of the vapor molecules, moving randomly over the liquid, return to it again. The wind carries away the molecules that fly out of the liquid and does not allow them to return.

Condensation can also occur when the vapor is not in contact with the liquid. It is condensation that explains, for example, the formation of clouds: molecules of water vapor rising above the ground, in the colder layers of the atmosphere, are grouped into tiny droplets of water, the accumulations of which are clouds. The condensation of water vapor in the atmosphere also results in rain and dew.

During evaporation, the liquid cools and, becoming colder than the environment, begins to absorb its energy. During condensation, on the contrary, a certain amount of heat is released into the environment, and its temperature rises slightly. The amount of heat released during condensation of a unit mass is equal to the heat of evaporation.