For this task you can get 1 point on the exam in 2020
The thermal equilibrium and everything is connected with it, the task of 10 exam in physics is devoted. Tickets are built so that in about half of them there are questions dedicated to humidity (a typical example of such a task "how many times the concentration of steam molecules increased, if the pair volume is isothermally decreased by two times), the rest concern the heat capacity of the substances. Questions on heat capacity almost always contain a schedule that must be pre-examined for a correct answer to the question.
The task 10 of the physics in physics usually causes complexity among students, except for several options that are devoted to the definition of relative air humidity in psychrometric tables. Most often, schoolchildren begin to fulfill the tasks from this question, the solution of which is usually one or two minutes. Loss of the Ticket Student It is with such a type of task number 10 of the exam in physics will greatly facilitate all the test, since the time for its implementation is limited to a certain number of minutes.
Humidity is a measure that characterizes the content of water vapor in the air. Relative humidity is the amount of water contained in the air at a given temperature as compared with the maximum amount of water, which may be contained in the air at the same temperature as a pair.
In other words, relative humidity shows how much more moisture is missing that condensation began under these environmental conditions. This value characterizes the degree of air saturation with water vapor. When calculating the optimal humidity of air indoors, it is about relative humidity.
- For example, at a temperature of 21 ° C, one kilogram of dry air may contain up to 15.8 g of moisture. If 1 kg of dry air contains 15.8 g of water, they say that the relative humidity of the air is 100%. If the same amount of air contains 7.9 g of water at the same temperature, then, compared with the maximum possible amount of moisture, the ratio will be: 7.9 / 15.8 \u003d 0.50 (50%). Consequently, the relative humidity of such air will be 50%.
What moisture is optimal
The ideal humidity in the residential room is 40-60%. In the summer months, the air is sufficiently moistened (in particularly rainy weather, relative humidity can reach 80-90%), therefore there is no need for additional moisture methods.
However, in winter, central heating systems and other heating appliances lead to single air. This is because strong heating increases the temperature, but does not increase the amount of water vapor. It causes an increased evaporation of moisture from everywhere: with your skin and from your body, indoor plants and even furniture items. Relative humidity in winter apartments is usually no more than 15%. It is even less than in the Sahara desert! There relative air humidity is 25%.
Table optimal humidity Demonstrates how insufficient level is 15%:
How to achieve optimal humidity?
The only advice is to moisturize the room.
There are many "folk" moisture methods. You can, for example, hang wet towels and rags in the room. Put the tank with water on the heater. Water evaporation sooner or later will lead to an increase in air humidity. To protect the piano from drying, they used to be put to put inside a jar with water. An option for those who do not regret money - a decorative fountain in the room.
However, the listed methods are inconvenient and ineffective. To significantly increase the humidity of the air in the room using a jar with water will not work. In addition, the bank on the battery and towels on the ropes look not very aesthetic.
The most effective and practical way to increase the indoor moisture is to establish humidifier. This climatic device is able to maintain a precisely specified humidification level, besides, it is inexpensive and easy to use. And the new generation of moisturizers themselves control the optimal humidity.
Air to some extent filled with water vapor. Its amount is characterized by such an indicator as humidity. It can be absolute and relative. The first indicator indicates the volume of water contained in one cubic meter of air. The second term is used to determine the ratio between the maximum possible number of steam to the real. If the indoor air humidity is determined, there is a relative indicator.
Why measure and monitor moisture indoors?
Humidity in the house directly affects the health and well-being of all its inhabitants. If the indicators do not correspond to the norm, not only people, but also indoor plants, furniture and other things suffer. The amount of water vapor in the environment is not stable and all the time varies depending on the time of year.
What is dangerous to the air?
Low moisture in the room is very often observed in the heating season. This leads to the fact that a person quickly loses water through the skin and respiratory tract. As a result of such negative phenomena, the following effects are observed:
- reducing the elasticity and dryness of the skin, which is accompanied by the appearance of microcracks, leads to the development of dermatitis;
- the drying of the mucous eye leads to their redness, burning, tearing;
- blood loses part of the liquid component, which reduces the speed of its movement, creating an additional load on the heart;
- a person suffers from headaches, feels fatigue and loses its usual performance;
- the viscosity of the gastric juice increases, which worsens the digestion;
- there is a drying of the mucous membranes of the respiratory tract, which weakens local immunity;
- increased concentration in the air of pathogenic microorganisms, which are usually neutralized by air droplets.
To measure air indicators in the apartment, it is enough to buy the simplest device that is usually combined with a thermometer or a clock. It has a small error of 3-5%, which is not critical.
Using a glass with water
To determine the humidity of the air, it is necessary to dial water into an ordinary glass and send it to the refrigerator for 3 hours so that the liquid coil up to 3-5 ° C. The vessel is taken out and put on the table away from the heating devices. For a few minutes, there are glasses over the walls of the glass, where the appearance of condensate in the form of water droplets is found. The results of the experiment are expressed as follows:
- glass dried quickly - humidity lowered;
- the walls remained duned - in the room of humidity standards are observed;
- the water began to drain water - the humidity is increased.
Table Assman
The assum table is designed to determine humidity with a psychrometer. It consists of two thermometers - usual and with moisturizing function. The indicators measured by the second instrument will be slightly lower. According to the special table using the values \u200b\u200bobtained, the humidity of the air is determined.
Using fir bishi
Take a conventional spruce bump and put it away from heating devices. With dry air, it will open its flakes, and with wet - they will be densely degraded.
Generally accepted norms
The norms of humidity in the room depends on its purpose and the time of year. Compliance with the recommended parameters will ensure good health, and will not negatively affect the immunity of a person.
Norms for apartment
For the apartment, all the rules regarding climate parameters are listed in GOST 30494-96. According to this document, air humidity during the cold season should be fluctuated in the range of 30-45%, and in the warm - 30-60%. Despite the specified values, the index of 30% may be badly perceived by the human body. Therefore, doctors recommend maintaining parameters of 40-60%, which are considered optimal at any time of the year.
Norms for the children's room
The child's body is unable to work correctly at low humidity. This leads to a rapid dryness of the mucous membranes, which is fraught with a decrease in local immunity.
Workplace
The moisture rate in the workplace depends on the specifics of labor. For example, for office workers, it is 40-60%.
How to normalize the microclimate indoors?
So that the microclimate in the room was comfortable for living, you need to take advantage of such advice:
- the use of humidifiers. Indispensable to the heating season in any rooms;
- regular ventilation;
- an increase in the number of indoor plants;
- the presence of exhaust ventilation. The supply extractor will supply the room with fresh air and normalizes the amount of water vapor;
- in some cases, it is recommended to use special air dryers equipped with absorbent substances;
- in residential premises, it is forbidden to dry underwear, which negatively affects their microclimate.
Video: How to measure air humidity
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I-17 \u003d ""\u003e saturated couples, air humidity
Today's lesson we will dedicate to the discussion of such a concept as air humidity, and methods of its measurement. The main phenomenon affecting the humidity of the air will be the process of evaporation of water, which we have already spoken earlier, and the most important concept that we will use will be rich and unsaturated steam.
If you select various steam states, then they will be determined in which the pairs interacts with its liquid. If you imagine that some liquid is in a closed vessel and the process of its evaporation occurs, then sooner or later this process will come to a state when evaporation at equal intervals will be compensated by condensation and the so-called dynamic equilibrium of fluid with its steam will come (Fig. 1) .
Fig. 1. Saturated par
Definition.Saturated steam - It is a pair located in thermodynamic equilibrium with its liquid. If the pair is not saturated, there is no such thermodynamic equilibrium (Fig. 2).
Fig. 2. Unsaturated Par
With the help of these two concepts, we will describe such an important air characteristic as humidity.
Definition.Air humidity - The value indicating the content in the air of the water vapor.
The question arises: why the concept of humidity is important for consideration and how do water vapors enter the air? It is known that the water (world ocean) occupies most of the ground, from the surface of which the evaporation continuously occurs (Fig. 3). Of course, in various climatic zones, the intensity of this process is different, which depends on the average daily temperature, the presence of winds, etc. These factors determine the fact that in certain places the water vaporization process is more intense than its condensation, and in some - on the contrary. On average, it can be argued that the steam that is formed in the air is not saturated, and its properties must be able to describe.
Fig. 3. Fluid evaporation (source)
For a person, moisture is a very important environmental parameter, since our body reacts very actively to its changes. For example, such a mechanism for regulating the functioning of the body, as a sweating, is directly related to the temperature and humidity. With high humidity, the process of evaporation of moisture from the surface of the skin is virtually compensated for by the processes of its condensation and the heat dissipation is disturbed from the body, which leads to the thermoregulation disorders. With low humidity, moisture evaporation processes prevail over condensation processes and the body loses too much fluid, which can lead to dehydration.
The magnitude of humidity is important not only for humans and other living organisms, but also for the flow of technological processes. For example, due to the known properties of water, its electrical current is carried out in the air can seriously affect the correct operation of most electrical appliances.
In addition, the concept of humidity is the most important criterion for estimating weather conditions, which everyone is known to weather forecasts. It is worth noting that if we compare humidity at different times of the year in the usual climatic conditions, it is higher in summer and below in winter, which is due, in particular, with the intensity of evaporation processes at different temperatures.
Absolute humidity
The main characteristics of wet air are:
- water vapor density in the air;
- relative humidity.
Air is a composite gas, it contains many different gases, including water vapor. To estimate its quantity in the air, it is necessary to determine which weight there are water vapors in a certain dedicated volume - such a value characterizes the density. Water vapor density in the air is called absolute humidity.
Definition.Absolute humidity - the amount of moisture contained in one cubic air meter.
Designationabsolute humidity: (as well as an ordinary density designation).
Unitsabsolute humidity: img \u003d ""\u003e
mass of steam (water) in the air, kg (in C) or g;
I-19 \u003d ""\u003e relative air humidity
To describe such perception, this value is introduced as relative humidity.
Definition.Relative humidity - The value showing how far the par from saturation.
That is, the magnitude of relative humidity, simple words, shows the following: if the pairs are far from saturation, then the humidity is low, if close is high.
Designationrelative humidity: .
Unitsrelative humidity: %.
Formula calculations relative humidity:
Img \u003d "" i-20 \u003d ""\u003e condensation hygrometer
As can be seen from the formula, the absolute humidity appear in it, with which we are already familiar, and the density of the saturated pair at the same temperature. There is a question how to determine the last magnitude? For this there are special devices. We'll consider condensationhygrometer (Fig. 4) - a device that serves to determine the dew point.
Definition.Dew point - Temperature at which couple becomes saturated.
Fig. 4. Condensation hygrometer (source)
Inside the tank of the device poured an easy-to-sleep fluid, for example, the ether, the thermometer (6) is inserted and the air is poured through the container with a pear. As a result of enhanced air circulation, an intensive evaporation of the ether begins, the temperature of the capacity is reduced due to this and the mirror performs dew (the droplets of the condensed pair). At the time of the appearance of dew on the mirror using a thermometer, the temperature is measured, this temperature is also a dew point.
What to do with the resulting temperature value (dew point)? There is a special table in which the data is entered - which density of the saturated water vapor corresponds to each specific dew point. It should be noted a useful fact that with increasing the value of the dew point, the value of the corresponding saturated pair density is growing. In other words, the warmer air, the greater the amount of moisture it can contain, and vice versa, than the air is colder, the maximum content in it is less.
Hair hygrometer
We now consider the principle of action of other types of hygrometers, instruments for measuring humidity characteristics (from Greek. Hygros - "wet" and Metreo - "Measure").
Hair hygrometer (Fig. 5) - a device for measuring relative humidity in which hair acts as an active element, for example, human.
Fig. 5. Hair hygrometer (source)
The effect of the hairless hygrometer is based on the property of a skimped hair to change its length when the air humidity changes (with increasing moisture, the hair length increases, with a decrease - decreases), which allows measuring relative humidity. Hair is stretched on a metal frame. The change in the length of the hair is transmitted by the arrow moving along the scale. It should be remembered that the hair hygrometer does not give exact values \u200b\u200bof relative humidity, and is used mainly in domestic purposes.
Psychrometer
More convenient to use and accurately, such a device for measuring relative humidity, as a psychrometer (from Dr.-Greek. Ψυχρός - "Cold") (Fig. 6).
The psychrometer consists of two thermometers that are fixed on the general scale. One of the thermometers is called wet, since it is wrapped with a batter cloth, which is immersed in a water tank located on the back of the instrument. With wet fabric, water evaporates, which leads to cooling the thermometer, the process of reducing its temperature lasts until the step is reached until the pairs near the wet tissue reach saturation and the thermometer will not start showing the temperature of the dew point. Thus, a wet thermometer shows a temperature less than either equal to the real ambient temperature. The second thermometer is called dry and shows the real temperature.
On the instrument housing, as a rule, an even so-called psychrometric table is depicted (Table 2). Using this table by the value of the temperature that the dry thermometer shows, and on the temperature difference between dry and wet thermometers, the relative humidity of the surrounding air can be determined.
However, not even having such a table at hand, you can roughly determine the value of humidity using the following principle. If the testimony of both thermometers is close to each other, the evaporation of water from the wet is almost completely compensated by condensation, i.e. the humidity is high. If, on the contrary, the difference in thermometers is large, then evaporation from wet fabric prevails over condensation and dry air, and the humidity is low.
Tables characteristics of humidity
Turn to tables that allow you to determine the characteristics of air humidity.
Temperature,
Pressure, mm. RT. Art.
Pair density
A little water was poured into the glass flask and closed it with a plug. Water gradually evaporated. At the end of the process on the walls of the flask, only a few drops of water remained. The figure shows a concentration timeline n.water couple molecules inside the flask. What statement can be considered correct?
o 1) On a plot of 1 pairs, saturated, and in the section 2 - unsaturated
o 2) On the section 1 pairs, unsaturated, and in the section 2 - saturated
o 3) on both sections of couples saturated
2. Task No.D3360E.
Relative air humidity in a closed vessel 60%. What will be relative humidity, if the volume of the vessel at a constant temperature is 1.5 times?
5. TASK №4AA3E9
Relative indoor air humidity at 20 ° С
70% is equal. Using the table of pressure of saturated vapor water, determine the pressure of water vapor indoors.
o 1) 21.1 mm Hg. Art.
o 2) 25 mm RT. Art.
o 3) 17.5 mm Hg. Art.
o 4) 12.25 mm Hg. Art.
32. Task 230B9.
The relative humidity of air indoors at a temperature of 20 ° C is 70%. Using the table of density of saturated vapor water, determine the mass of water in the cubic meter of the room.
o 3) 1,73⋅10 -2 kg
o 4) 1,21 €10 -2 kg
33. Task number DDFF058
On Ri-Song-Ke-Ra-Ra-Sun: X-Tir-Tire Li-Ni-her - Gra-Fick in the V-Si-Mo Davréniya on-Syuchny Varia WATERS OF THE TE-PE-RA-TU-RL, and SPL-NO-NIH - PRO-CESS 1-2, due to par-qi-al-na-giving vapor water.
As the past due to the passage of Par-Qi-Al-na-giving vapor vapor AB-CO-Lyut-naya wetland
1) uve-li-chi-va
2) Reduz-Sha-ET-Xia
3) not from me - it
4) maybe it is uve-chi-to-y, so dechat-shat-sm
34. Task 230B9
For the defo-de leuya of the non-Si-tel moisture-ni-stub, the difference is the difference of the Sous-Ho and moist-no-th therm-MET-MOD (see Ri-Su-Nok). IS-Paul-Dan-Ri-Song and Psi-Chron-Met-Ri-Chelya Tab Li Tsu, OPRA-de-La-Th-Rou-Tu-Ru ( In GR-Du-Sah, a goal) in ka-zy-vasya, the terr-Mo-meter, if from-na-tel-naya wetland of WHO Du-HA in inherited 60%.
35. Task number DDFF034
In Co-Su-de Under Porsch-it, on-Ho-diet-Xia, non-na-schenny couples. It can be re-ve-pieces in on-son-puned
1) iso-bar, but in vya-la-ra-tu-ru
2) pre-Bav-Lyaya in the vessel of a friend gas
3) Utensu-Li-Chi-Way Couple
4) decreased steam
36. Task number 9C5165
From-no-tel-na wedliness of the WHO Du-ha in whose one is equal to 40%. Ko-co-in-one-niene con-price-traction n. Mo-le-cooler of water in the WHO Du-Hom-on-You and Kon-price-traction of the Mo-le-cooler of water in the Nas-Schuchenn-Mr. Pare at the same PE-RA-TU?
1) N mini 2.5 times
2) N pain 2.5 times
3) n mini-neck by 40%
4) N \u200b\u200bpain 5%
37. Task №DFF058.
From-no-tel-nai wedliness of the WHO Du-HA in the Qi-Lin-Dre Under Porsch is 60%. The WHO-Spirit of Iso Ter Mi-Che-Ski squeezed, reduced its volume twice. From-ni-tel-naya moisture
38. Task №1Be1aa.
In the suture of Qi-Lin-Drei-Che-SO-SU-DI-Ho-Dit-Si-Dita, the wet-oh spirit at the temperature of the PE-RA-Tu 100 ° C. In order for the walls of this co-su-yes you-pa-la Rosa, Tre-Buzz iso-ter-Mi-Che-Ski from me-thread volume co-su-yes at 25 time. What is the priest-zo-tel, but is equal to the per-in-law of the AB-SO-Lyut-Naya Waist of WHO Du-ha in So-Su-de? The response is the re-di in g / m 3, the district-lyu-same to the whole.
39. Task №0B1D50
In the cylindrical vessel under the piston for a long time there are water and its pairs. The piston begin to push the vessel. At the same time, the temperature of the water and the steam remains unchanged. How will the mass of fluid in the vessel change? Reply explain by specifying which physical laws you used to explain
40. Task №C32A09
In the cylindrical vessel under the piston for a long time there are water and its pairs. The piston is beginning to move into the vessel. At the same time, the temperature of the water and the steam remains unchanged. How will the mass of fluid in the vessel change? Reply explain, indicating which physical patterns you used to explain.
41. Task №AB4432.
In the experiment illustrating the dependence of the boiling point from air pressure (Fig. but ), Water boiling under the bell of the air pump occurs at room temperature, if the pressure is enough.
Using a pressure dependence schedule saturated para From temperature (fig. b. ), Specify which air pressure must be created under the bell of the pump so that water boils at 40 ° C. The answer explain, indicating which phenomena and patterns you used to explain.
| (but) | (b.) |
42. Task 2295d.
Relative air humidity with t. \u003d 36 o C is 80%. Saturated steam pressure at this temperature p. N \u003d 5945 Pa. What pair mass is contained in 1 m 3 of this air?
43. Task number 9C5165
A man in glasses entered the street in a warm room and discovered that his glasses were fucked. What should be the temperature on the street so that this phenomenon is observed? In the room, the air temperature is 22 ° C, and the relative air humidity is 50%. Explain how you got the answer. (When answering this question, use the table for the pressure of saturated vapor water.)
44. Task 2295d
In the Gran-Dyat-Su-de-Ho-Dyat-Si-Dya-Ho-Dyat-Xia, a non-co-human water. How is it from me-nyat, with an Izo-Mi-Che-Soy-Soy Nii of the E-Ma Co-Su-Da-Du-Du-resident three ve-li-chives: giving -He-su-de, water mass, steam mass? For each ve-Li-Opera-de-Li-Th-from-vet-the-human ha-rack-terrace:
1) uve-lei-cheat-xya;
2) reducer-shit-sm
3) not from me-nit-sm.
In the Pi-Shi-te, in tab-li-tsu youird numbers for each Fi-Zi-Thieve ve-li-chi. Figures in from-ve-those can do-ours.
45. Task number 8BE996
Ab-co-lyut-nai wedliness of the WHO Du-ha, on-home-in-th, in Qi-Lin-Dry-Chech Socy-Su-de Under Porsch, is equal. The temperature of gas in co-su-de is equal to 100 ° C. As at some time, the Tre-buzz is the iso-ter Mi-Che-Ski-thread volume of co-su-yes in order for its walls by Obro-Zo-Va Rose?
1) reduce-to-sew at pribe-zi-tel-but 2 times 2) uve-li-even at-prin-zi-tel-but 20 times
3) reduce-to-sew at the priest-zi-tel-but at 20 times 4) uve-li-even 2 times
46. \u200b\u200bTask # 8Be999.
In the ex-la-r-men-make-nov-les, which, with the temperature, in the com-on, on the walls of a hundred-ka-on Ho-Lodnoy Water on-Chi-on-Xia Con-Den-Casual Water Vapor from WAO Du-Hay, if you smoke theme-per-ra-tu-ru hundred-ka-to . According to the re-zul-ta-there, these ex-pe-men-sets of the defo-de-ten-e-but-century moisture of WAO Du-ha. For the re-neck, yes-Chi Re-Paul-Zuy Tab-Li Tsei. From me-nit-xya from-no-tel-naya moisture when there is a one-e-do-tro-t-in-rya in com-on Con-Den-Caution of Water Vapor from Was-Du Hay will be on-si-by-Xia at the same ne-the-Ta-Tu-rep? Davith and the carnival of the on-son-ny-na-dya-th a couple with a single-person-in-time-ta-re-order -I-tse:
| 7,7 | 8,8 | 10,0 | 10,7 | 11,4 | 12,11 | 12,8 | 13,6 | 16,3 | 18,4 | 20,6 | 23,0 | 25,8 | 28,7 | 51,2 | 130,5 |
« Physics - Grade 10 »
When solving tasks, it should be borne in mind that the pressure and density of the saturated pair do not depend on its volume, and depend on temperature only. The equation of the state of the perfect gas is approximately applicable to describing saturated steam. But when compressed or heated saturated pair, its mass remains constant.
When solving some tasks, the saturated pair pressure may be needed at some temperatures. This data must be taken from the table.
Task 1.
The closed vessel volume V 1 \u003d 0.5 m 3 contains water with a mass M \u003d 0.5 kg. The vessel was heated to the temperature T \u003d 147 ° C. How much should the volume of the vessel be changed so that only saturated steam contains in it? Pressure of saturated vapor. P at a temperature T \u003d 147 ° C is 4.7 10 5 PA.
Decision.
Rich steam at pressure r n. P covers an amount of where m \u003d 0.018 kg / mol - molar mass of water. The volume of the vessel V 1\u003e V, and therefore steam is not saturated. In order for steam to become saturated, the volume of the vessel should be reduced on
Task 2.
The relative humidity of the air in a closed vessel at a temperature T 1 \u003d 5 ° C is Φ 1 \u003d 84%, and at a temperature T 2 \u003d 22 ° C. Φ 2 \u003d 30%. How many times the pressure of a saturated pair of water at a temperature T 2 is greater than at a temperature T 1?
Decision.
Water vapor pressure in a vessel at T 1 \u003d 278 to equals 
where r n. P1 is a saturated pair pressure at a temperature T 1. At temperatures T 2 \u003d 295 to pressure 
As the volume is constant, then by the law of Charles
From here 
Task 3.
In the room with a volume of 40 m 3 air temperature 20 ° C, its relative humidity φ 1 \u003d 20%. How much water to evaporate water so that the relative humidity φ 2 reached 50%? It is known that at 20 ° C, the pressure of saturated vapors r n n \u003d 2330 pa.
Decision.
Relative humidity 
From here
Couple pressure at relative humidity φ 1 and φ 2
The density is associated with pressure equality ρ \u003d MP / RT, from where
Mass of water in the room with humidity φ 1 and φ 2
The mass of water to evaporate:
Task 4.
In the room with closed windows at a temperature of 15 ° C relative humidity φ \u003d 10%. What will be the relative humidity equal if the temperature in the room will rise by 10 ° C? Pressure of saturated steam at 15 ° C r. P1 \u003d 12.8 mm Hg. Art., and at 25 ° C p2 \u003d 23.8 mm Hg. Art.
Since the pair is unsaturated, the partial pressure of the steam changes under the law of the chall p 1 / t 1 \u003d p 2 / t 2. From this equation, it is possible to determine the pressure of an unsaturated pair P 2 at T 2: p 2 \u003d p 1 t 2 / t 1. Relative humidity at T 1 is equal.
Saturated steam.
If Vessel S. The liquid is tightly closed, then first the amount of fluid will decrease and then remain constant. With nonsensemenn. temperature system Liquid - pairs will come to a state of thermal equilibrium and will be in it how many things will be. Simultaneously with the process of evaporation, condensation occurs, both processes on average computerensure each other. At the first moment, after the fluid is poured into the vessel and close it, the fluid will beevaporate and the density of steam above it will increase. However, at the same time, the number of molecules returned to the liquid will grow. The greater the density of the steam, the greater the number of its molecules returns to the liquid. As a result, in a closed vessel, a dynamic (movable) equilibrium between liquid and steam, i.e., the number of molecules leaving the surface of the fluid for some kind of moleculesr after a period of time, it will be equal to an average number of steam molecules that returned during the same time in liquidb Par, na pandering in dynamic equilibrium with its liquid is called a saturated ferry. This is the definition of the underlineit makes that in this amount at this temperature there can be a greater number of steam.
Saturated Para Pressure .
What will happen to a saturated ferry if you reduce the volume occupied by it? For example, if you compress steam, located in equilibrium with a liquid in the cylinder under the piston, maintaining the temperature of the contents of the cylinder constant. When compressing a pair, the equilibrium will begin to break. The density of the steam at the first moment will slightly increase, and a larger number of molecules will begin from gas to the liquid than from the liquid in the gas. After all, the number of molecules leaving the liquid per unit of time depends only on temperature, and steam compression This number does not change. The process continues until the dynamic equilibrium and the pair density is not yet established, and therefore the concentration of its molecules will not take their previous values. Consequently, the concentration of rich steam molecules at a constant temperature does not depend on its volume. Since the pressure is proportional to the concentration of molecules (P \u003d NKT), then this definition follows that the pressure of the saturated pair does not depend on the volume occupied by it. Pressure P N.P. A pair in which the fluid is in equilibrium with its ferry, is called a pressing of a saturated pair.
The dependence of the pressure of saturated steam on temperature.
The status of a saturated steam, as the experience shows, is approximately described by the equation of the state of the ideal gas, and its pressure is determined by the formula P \u003d NCT with increasing temperature pressure grows. Since the pressure of a saturated pair does not depend on the volume, then, therefore, it depends only on temperature. However, dependence R N.P. From t, found experimentally, is not directly proportional to the ideal gas at a constant volume. With increasing temperature, the pressure of a real saturated pair grows faster than the pressure of the perfect gas (Fig.stock curve 12). Why is this happening? When the fluid is heated in a closed vessel, part of the fluid turns into steam. As a result, according to the formula P \u003d Nofto, the saturated steam pressure increases not only due to the increase in fluid temperature, but also due to an increase in the concentration of molecules (density) of steam. Basically, the increase in pressure with increasing temperature is determined precisely by an increaseentraz aI. (The main difference in behavior anddeal gas and a saturated pair is that when the temperature is changed in the closed vessel (or when the volume is changed at a constant temperature), the pair weight changes. The liquid is partially turning into pairs, or, on the contrary, pairs are partially condensedtsya. With perfect gas, nothing like this happens.). When all liquid evaporates, steam with further heating will cease to be saturated and its pressure at a constant volume will be ageit is directly proportional to absolute temperatures (see Fig., Curve 23).
Boiling.
Boiling is an intense transition of a substance from a liquid state into a gaseous, which occurs throughout the volume of fluid (and not only from its surface). (Condensation - reverse process.) As the fluid temperature increases, the evaporation intensity increases. Finally, the liquid begins to boil. When boiling throughout the volume of the liquid, rapidly growing steam bubbles are formed, which float to the surface. The boiling point of the liquid remains constant. This is because all the energy supplied to the fluid is spent on turning it into pairs. Under what conditions does boiling begins?
In the liquid there are always dissolved gases that are released at the bottom and walls of the vessel, as well as on the drains weighted in the liquid, which are vaporization centers. Pair of liquids inside bubbles are saturated. With increasing temperature, the pressure of saturated vapors increases and bubbles increase in size. Under the action of the pushing force, they pop up. If the upper layers of fluid have a lower temperature, then the steam condensation occurs in these layers in bubbles. Pressure falls rapidly, and bubbles slam. The slamming occurs so quickly that the walls of the bubble, facing something like an explosion. Many such microcrust creates a characteristic noise. When the fluid warms down enough, the bubbles will stop slapping and surfaced to the surface. Liquid boils. Watch carefully behind the kettle on the stove. You will find that before boiling he almost ceases to noise. The dependence of the pressure of a saturated steam on temperature explains why the boiling point of the fluid depends on the pressure on its surface. A pair bubble can grow when the saturated pair pressure inside it slightly exceeds the pressure in the liquid, which is from the pressure of the air to the surface of the fluid (external pressure) and the hydrostatic pressure of the liquid column. Boiling begins at a temperature at which the saturated vapor pressure in bubbles is compared with pressure in the liquid. The greater the external pressure, the higher the boiling point. Conversely, reducing the external pressure, we are therefore lowering the boiling point. Puming the air and pair of water from the flask, you can get the water boiled at room temperature. Each liquid has its own boiling point (which remains constant until all the liquid is popped by), which depends on the pressure of its saturated steam. The higher the saturated steam pressure, the lower the boiling point of the fluid.
Air humidity and its measurement.
In the surrounding air, there is almost always a certain amount of water vapor. Air humidity depends on the amount of water vapor contained in it. Raw air contains a greater percentage of water molecules than dry.Pain the relative humidity of the air has a difference, the reports of which every day sound in the reports of the meteoprognosis.
Titlethe poor humidity is the ratio of the density of the water vapor contained in the air, to the density of the saturated pair at a given temperature, expressed as a percentage (shows how much water vapor is close to saturation).
Dew point
The dryness or humidity of the air depends on how close is its water vapor to saturation. If the wet air is cooling, then the steam located in it can be brought to saturation, and then it will be condensed. A sign that steam was saturated is the appearance of the first droplets of the condensed liquid - dew. The temperature in which steam in the air becomes saturated, is called a dew point. The dew point also characterizes air humidity. Examples: dew loss in the morning, fogging cold glass, if you breathe on it, the formation of water drops on a cold water pipe, dampness in the basements of houses. Measuring instruments are used to measure air humidity - hygrometers. There are several types of hygrometers, but the main: hair and psychrometric.
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