water vapor

Among real gases, water vapor occupies a special place. It has become very widespread in many fields of technology and is used as a coolant in power plants. Water vapor is typically used at pressures and temperatures where it must be treated as a real gas. Water vapor can be obtained in two ways: by evaporation and boiling water.

Evaporation is the process of formation of steam from water, occurring only from the free surface. This process occurs at any temperature. During evaporation, molecules with the highest kinetic energy break off from the surface of the water and fly into the surrounding space. As a result, water vapor forms above the liquid. The intensity of the evaporation process increases with increasing temperature.

Boiling is the process of formation of water vapor throughout the entire volume of liquid. When heated to a certain temperature, vapor bubbles form inside the liquid, which, connecting with each other, fly out into the surrounding space. In order for a vapor bubble to form and then grow, it is necessary that the process of vaporization occur inside the bubbles, and this is only possible if the kinetic energy of the water molecules is sufficient for this. Since the kinetic energy of molecules is determined by the temperature of the liquid, therefore, boiling at a given external pressure can begin only at a very specific temperature. This temperature is called the boiling point or saturation temperature and is denoted tb. The boiling point at a given pressure remains constant until all the liquid turns into vapor.

The steam formed above the surface of a boiling liquid is called saturated steam. Saturated steam can be dry or wet. Dry saturated steam is such steam that, being above the surface of a boiling liquid, does not contain suspended droplets of liquid. Wet saturated steam, or simply wet steam, is a mechanical mixture of dry saturated steam and boiling liquid. A characteristic of wet steam is its degree of dryness x. The degree of dryness is the proportion of dry saturated steam in wet steam, i.e. the ratio of the mass of dry saturated steam in wet steam to the mass of wet steam. The value 1-x is called the degree of humidity or the humidity of moist saturated steam, i.e. mass fraction boiling liquid in moist air. The parameters that completely determine the state of dry saturated steam or boiling liquid are temperature or pressure and the degree of dryness.

If heat is supplied to dry saturated steam in the absence of a boiling liquid at the same pressure as the pressure of dry saturated steam, then it will turn into superheated steam. His temperature will begin to rise. Superheated steam is steam that has more high temperature at a given pressure than dry saturated steam. The temperature of superheated steam is designated by the letter t, and the temperature difference t–t n is called the degree of superheat, or steam superheat. With increasing superheating of the steam, its volume will increase, the distance between the molecules will increase and, consequently, the forces of mutual attraction will decrease, i.e. superheated steam at high degrees of superheating will approach in its properties to an ideal gas. The parameters that determine the state of superheated steam will be pressure and temperature (or specific volume).

The process is the reverse of vaporization, i.e. The process of transition of vapor into liquid is called the condensation process.

When I hear the word "steam", I remember the times when I was still in primary school. Then, when parents came home from school, they started preparing lunch and put a pan of water on gas stove. And after ten minutes, the first bubbles began to appear in the saucepan. This process has always fascinated me, it seemed to me that I could look at it forever. And then, some time after the bubbles appeared, the steam itself began to flow. One day, I asked my mother: “Where are these white clouds coming from?” (That's what I used to call them). To which she answered me: “This all happens due to the heating of the water.” Although the answer did not give a complete picture of the process of steam formation, in my school physics lessons I learned everything I wanted about steam. So...

What is water vapor?

From a scientific point of view, water vapor is simply one of three physical states of the water itself. It is known to occur when water is heated. Like herself, the steam has no color, no taste, no smell. But not everyone knows that clouds of steam have their own pressure, which depends on its volume. And it is expressed in pascals(in honor of the well-known scientist).

Water vapor surrounds us not only when we cook something in the kitchen. It is constantly contained in the street air and atmosphere. And its content percentage is called "absolute humidity".

Facts about water vapor and its features

So, a few interesting points:

• the higher the temperature, which acts on water, the faster the evaporation process occurs;
• besides this, evaporation rate increases with area size the surface on which this water is located. In other words, if we start heating a small layer of water on a wide metal cup, then evaporation will occur very quickly;
• Plant life requires not only liquid water, but also gaseous water.. This fact can be explained by the fact that evaporation constantly flows from the leaves of any plant, cooling it. Try to touch a tree leaf on a hot day and you will notice that it is cool;
• the same applies to humans, the same system works with us as with plants above. The fumes cool our skin on a hot day.. Surprisingly, even with light loads, our body leaves about two liters of fluid per hour. What can we say about increased stress and hot summer days?

This is how we can describe the essence of steam and its role in our world. I hope you discovered a lot of interesting things!

What other substances, besides gases, are part of air?

1. Distribution of water vapor in the air. After the rain, you have all watched how the roofs of houses, tree trunks and leaves get wet, and puddles form everywhere. After the clouds dissipate, the Sun appears and everything around dries up. Where does it disappear without a trace? rainwater? It turns into water vapor. Since it is colorless, like air, we do not see it.
Any air contains a certain amount water in the form of water vapor. Water particles in the form of steam are also contained in the air in the room. This is not difficult to notice. In winter, pay attention to metal objects (briefcase lock, skates, etc.) brought home from the street. After a while they begin to “sweat.” This means that warm air in the room, in contact with a cold object, it releases droplets of water.
The moisture of the earth's surface evaporates from the soil, swamps, rivers, lakes, seas and oceans in the form of water vapor into the atmosphere. A large amount of water (86%) evaporates from the oceans and seas.
In nature, water vapor is in a continuous cycle. Water vapor rises above the oceans and land surfaces and enters the atmosphere. Air currents carry it with them to other places. Water vapor, in turn, cools, turns into clouds, and in the form of precipitation it returns to the surface of the Earth.

2. Dependence of water vapor in the air on temperature. The content of water vapor in the air depends on the state of the evaporated surface and temperature. There is a lot of water vapor in the air over the ocean, but little over land. In addition, the higher the temperature, the greater the water vapor content in the air.

As can be seen from the table, air can contain water vapor at a certain temperature. If the air contains as much water vapor as it can contain at a given temperature, then it is called saturated. For example, to saturate 1m3 of air with water vapor at a temperature of +30°C, 30 g of water vapor is required. If the amount of water vapor is only 25 g, then the air will be unsaturated and dry.
As the temperature rises, saturated air becomes unsaturated. For example, to saturate 1m3 of air at a temperature of 0°C, 5 g of water vapor is required. If the air temperature rises to +10°C, then 4 g of water vapor will not be enough to saturate the air.

3.Absolute and relative humidity. The content of water vapor in the air is determined by absolute and relative humidity.
Absolute humidity is the amount of water vapor in grams in 1 m3 of air (g/m3).
Relative humidity is the ratio of the amount of moisture present in 1 m3 of air to the amount of water vapor that saturates the air at a given temperature. Relative humidity is expressed as a percentage.
Relative humidity shows the degree of saturation of air with water vapor. For example, 1 m3 of air can contain 1 g of water vapor at a temperature of -20°C. The air contains 0.5 g of moisture. Then the relative humidity is 50%. When the air is saturated with water vapor, the relative humidity reaches 100%.

4. Condensation of water vapor. After the air is saturated with water vapor, the remaining amount of steam turns into water droplets. If 1 m3 of air at a temperature of -10°C instead of 2 g of water vapor collects 3 g, then the extra 1 g of steam turns into water droplets. When the temperature of saturated air decreases, it cannot hold as much water vapor. For example, to saturate 1 m3 of air at +10°C you need 9 g of water vapor. If the temperature drops to 0°, then the air can only hold 5 g of water vapor, the remaining 4 g turn into water droplets.
Under certain conditions, the transition of water vapor into a liquid state (water droplets) is called condensation (in Latin condensation- condensation). At a temperature of 0°C, water vapor turns into a solid state, i.e. turns into ice crystals.

5. Air humidity measurement. Relative humidity is measured using a device - hair hygrometer(in Greek hygros - wet, meter- measure). This device takes advantage of the property of human hair that lengthens when humidity increases. When humidity decreases, hair shortens. The hair is attached to the arrow of the dial; when lengthening or shortening the hair, the arrow, moving along the dial, shows relative humidity in percent (Fig. 54).

Rice. 54. Hair hygrometer.

The hygrometer, like a thermometer, is placed in a meteorological booth.
At weather stations, air humidity is determined using more accurate instruments and using special tables.

1. Why is the content of water vapor in the air above the equator greater than in the temperate zone?

2. What happens to water vapor in the air as altitude changes?
3. Air temperature +10°C. Absolute humidity 6 g/m3. Under what conditions will the air become saturated with water vapor? (Solve in 2 ways.)
4. Familiarize yourself with the structure of the hygrometer and measure the relative humidity.

5*. The air temperature is +30°C, and the absolute humidity is 20 g/m3. Calculate relative humidity.

Question 1. In what states of aggregation can water exist?

1) Solid - ice, 2) Liquid - water, 3) Gaseous - steam.

Question 2. How are they different? states of aggregation from each other?

The state of aggregation of a substance is determined by the location, nature of movement and interaction of molecules.

Question 3. Can precipitation fall from sources other than clouds?

No, since precipitation is water in a liquid or solid state that falls from clouds or settles from the air onto the earth's surface and any objects.

Question 4: Why does fog occur more often either early in the morning or in the evening?

It is associated with a cold flow of air that descends onto the warm surfaces of land or water.

Question 5. What is water vapor?

Water vapor is water molecules. That is, water vapor is a gas.

Question 6. What is a cloud?

A cloud is a collection of small water droplets or ice crystals in the atmosphere.

Question 7. What types of clouds are there?

The main types of clouds are: stratus, cumulus, cirrus.

Question 8. List the types of precipitation.

Rain, shower, drizzle, snow, fog, hail, dew, frost.

Question 9. Does precipitation always fall from clouds?

Precipitation can fall from the air in the form of frost and dew when warm air comes into contact with a cold surface.

Question 10. What is air humidity?

Air humidity is a quantity characterizing the content of water vapor in the Earth's atmosphere.

Question 11. How is water vapor formed?

Water vapor is formed by water molecules when it evaporates.

Question 12. What is the main pattern of moisture distribution on the Earth's surface?

Since air humidity depends on air temperature, the air above the equator and over the oceans is always more humid than the air above the poles and continents.

Question 13. Why, other things being equal, does warm air contain more water vapor than cold air?

Because as the temperature rises, the evaporation process accelerates.

Question 14. What is the essence of the process of fog formation?

Fog is formed by condensation. In the morning, the Earth's surface cools down greatly. The air above it also cools. When air cools, like other substances, it contracts. The molecules of water vapor become cramped, they come closer and closer together. Finally they begin to collide with each other and form tiny droplets. They are so small that we cannot see each one individually, but together they form a fog.

Question 15. Under what conditions does condensation of water vapor occur in nature?

Condensation is the transformation of water vapor into a droplet (liquid) state. Condensation occurs when air cools.

Question 16. What is the difference between a cloud and a cloud?

The amount of water in the clouds exceeds the amount of water in the clouds, as a result of which excess moisture falls in the form of various precipitation: rain, snow or hail.

Question 17. Create a classification scheme for precipitation based on the text of the paragraph.

Question 18. Using the data given in the table, calculate the annual amount of precipitation.

Amount of precipitation per year: 10+15+ 20+25+15+10+5+5+15+20+25 +20=185 mm.

You, of course, have noticed that if you leave the river and do not dry yourself with a towel, then after a while your skin will become dry.

This means that the water on the surface of your body has evaporated. The process of evaporation is the transition of the liquid state of water to the vapor state. You can observe this phenomenon everywhere in nature.

Evaporation constantly occurs from the surface layer of seas and oceans, and wet objects (for example, when you wipe a school board with a wet rag).

All living beings and plants also undergo the process of evaporation. Thanks to this phenomenon, living organisms are able to regulate their body temperature. You've probably noticed that water evaporates faster from the surface of the body if it's windy outside or the sun is shining brightly.

Indeed, with rising temperatures and the presence of wind, evaporation occurs more intensely, so puddles dry out faster in summer than in autumn. In winter, this process slows down completely, but does not stop. Even wet laundry hung outside and covered with a crust of ice will still become dry. The evaporation process, even under such conditions, still continues. At a temperature of +100°C liquid state boiling water turns into vapor. At this moment, the most active evaporation process is observed.

The resulting steam from the surface of the earth begins to rise. You know that warm air is much lighter than cold air, which is why it begins to rise, rushing upward. But with increasing altitude, the air temperature begins to drop sharply, and the water cools, forming small droplets of water. This is how clouds appear that you can see in the sky every day. They may contain numerous droplets of water. These are water clouds. Some of them may contain small crystals. Such clouds are called ice clouds. And if both water droplets and crystals are observed in the composition, then they are mixed. Ice clouds form at the highest altitudes.

The process of formation of water droplets from steam is reverse process evaporation, it received the name - condensation (from Latin - “condensation”). In nature, you can observe this process when dew falls and fogs occur.

The phenomenon of condensation is also actively used in pharmacology. This way the water used for laboratory research and in the manufacture of medicines. The process consists of three stages: water is converted into steam, the steam returns to a liquid state, and the resulting droplets are collected by drainage (distillation). The result was distilled water. But it is not absolutely pure, because atmospheric air particles are mixed with it. An almost similar composition is observed in purified snow or rain water.

COMBINE USEFUL WITH PLEASANT !

Where does water come from?

Target

Introduce the process of condensation.

Materials

• hot water container
• mirror.

I held the cooled mirror over the steam. I examined the droplets of water that appeared on it. Where did this water come from?

This steam settled on the mirror and cooled, turning into water. We repeated the same thing, but with a warm mirror - there were very few drops of water.

Why?

The process of turning steam into water occurs when the steam cools.

Where does the water go?

Target

Identify the process of water evaporation, the dependence of the evaporation rate on conditions (air temperature, presence of wind).

Materials

• Three identical containers with the same amount of water.

You need to pour the same amount of water into the container, make a level mark and place it in different conditions: on the radiator, near the window and in a cool place (stand).

Now we observe the process of water evaporation, recording it in an observation diary.

Why?

Water evaporates faster in the heat (near the radiator), then near the window (wind - draft), and lastly in the cabinet (it’s cool there, no draft).

Does water vapor turn into water droplets?

You will need:

• .Kettle
• .Burner
• .Water
• .Metal mug
• A few ice waders and ice water

Process:

1. Fill the kettle with water.
2. Let the water boil.
3. Place a few ice cubes and ice water in a metal mug.
4. When the kettle boils, direct the steam stream towards the metal mug.

What is the result?

Water droplets appear on the outer surface of the metal mug.

Why?

Water vapor turns into water droplets when it comes into contact with a cold surface. This process, during which water changes from a gaseous state to a liquid state, is called “condensation.” Because the metal mug is much cooler than the boiling water in the kettle, the stream of steam coming out of it turned into droplets of water as soon as it touched the surface of the mug.