Saturated steam air humidity test. Physics test: “Evaporation, boiling and condensation, vapors, air humidity
Lesson type: combined.
Lesson form: lesson-game
Class: 8th grade.
Lesson objectives:
didactic- create conditions for learning new material on this topic, using elements of problem-based learning;
educational- to give students knowledge about the features of the physical processes of the transition of a substance from a liquid state to a gaseous state and vice versa, to teach schoolchildren to understand the micromechanism of these phenomena, to explain these processes from the point of view of molecular kinetic theory;
developing- to form an idea of the process of scientific knowledge, the development of logical thinking, and the development of practical skills in understanding the laws of physics;
educational- to develop the ability to apply acquired knowledge in practice to explain natural phenomena.
Lesson type: combined, using information technology.
Lesson form: lesson - game
Presentation.
Frontal experiments:
1. Dependence of evaporation rate on temperature, surface area, type of liquid, air movement
2. Cooling of liquid by evaporation.
Lesson plan.
I. Organizational moment.
II. Survey
1. Testing students’ knowledge (solving problems at the board)
2.Work with formula cards, checking knowledge of definitions.
3.Working with the dough.
III. Learning new material
1. Explanation of the phenomenon of evaporation from the point of view of MCT.
2. Evaporation as a physical phenomenon, its signs.
3. Factors affecting the rate of evaporation.
4. Condensation.
5.Saturated steam.
6. Evaporation in nature and technology.
IV. Consolidating new material
VI. Homework
VII. Lesson summary
I.Organizing time
“Good afternoon, guys and dear guests!
Today we have an unusual lesson.
Today in the lesson, you guys and I will go on an exciting journey to the “Land of Knowledge”
“Moment after moment, hour after hour,
Be amazed.
Everything will be like this and everything will be wrong,
In one moment.
We will take luggage for the trip:
Textbook, pen, pencil"
Teacher: We begin our journey on a magnificent, comfortable bus, boarding has already been announced, we enter the bus interior, we are greeted by calm music, we take our seats, the bus moves off and our exciting journey to the “Land of Knowledge” begins. But here is the first stop called "Did you know that..."
II. Survey:
Teacher: At this stop, 5 students will visit the pavilion "Solve the problem", but first they will receive tickets (children go to the board, take tickets with problems and solve them)
The rest will visit the pavilion with me " Did you know?"
You have cards laid out on your table, let’s work with them. Let's recall the previously studied material.
1). Please show me a card with a formula that calculates the amount of heat required to heat a body to a certain temperature.
Suggested answer: (Q= cm· (t2 - t1 ) )
Teacher: Read it, where: Q-... (amount of heat), C-...(specific heat capacity), m -... (body mass), (t2 - t1)-..., (temperature at which the body is heated). Please formulate the definitions : amount of heat, specific heat capacity.
Teacher: Please show me a card with a formula that calculates the amount of heat released during fuel combustion
Suggested answer : (Q = q· m)
Teacher: Read it, where Q- ... (amount of heat), q- ... (specific heat of combustion), and now please formulate the definition specific heat of combustion.
Teacher: Please show me a card with a formula that calculates the amount of heat required to melt a substance at its melting point.
Suggested answer : (Q = ۸ · m)
Teacher: Read it, where Q-...(amount of heat), ۸-...(specific heat of fusion). Please formulate a definition: specific heat of fusion.
Teacher: And now we will visit the pavilion "Definitions" and we will do the following type of work: I will show you the word written on the card, and you will give me the definition of this phenomenon or physical quantity. (On the card the teacher shows the words - internal energy, heat transfer, convection, radiation, thermal conductivity, melting, melting point, crystallization, crystallization temperature,)
Students give definitions.
For each correct answer, students receive a token - 1 token is 1 point.
Teacher: ..... will comment on the solution to his problem as the most difficult.
Students who have finished working at the board sit down and listen to her.
Okay, have a seat. Students put their grades in points on the evaluation sheet, which is on everyone’s desk. (for the correct solution of the problem 5 points, (for solving the problem with shortcomings 4 points)
Teacher: On the way there is a pavilion "Test" Let's visit it, we only have 3 minutes to visit this pavilion.
Teacher: And now we got up and stretched (a student conducts a physical education session)
Teacher: Our stop time has expired, let's hurry to our bus and continue our exciting journey. But then a cloud rolled in, blocked out the sun, and the rain pattered on the windows of the bus, and rivulets of water flowed down the windows. The rain suddenly stopped, just as it had started, the Sun came out and the streams of water on the windows disappeared. Where did the water go, what happened to it? (formulation of the problem)
Suggested answer: dried up, evaporated
III.Learning new material
Teacher: You will learn to answer this question and many other questions if you pay attention today in our travel lesson, the topic of which we will see on the slide (slide number 1 is shown - Lesson topic: “Evaporation.”Saturated and unsaturated steam.Condensation")
We open the notebooks, write down the number, class work and the topic of the lesson “Evaporation and condensation.”) Guys, open the dictionaries and write new words in your dictionary - evaporation, condensation.Today you guys and I will study these wonderful phenomena and get acquainted with their manifestations in life.
The bus pulls up to a chic stop called "Physical phenomenon" We enter the pavilion and see on the board questions that need to be answered. (slide 2).
1. In what states of aggregation can the same substance exist?
2.What is the difference between substances that are in different states of aggregation from the point of view of MCT? Slide 3.
3. What is the transition of a substance from solid to liquid called?
4. Under what conditions does melting occur?
5. What process is called hardening?
Teacher. And today our task is to consider the process of transition of a substance from a liquid state to a gaseous state (vaporization) and vice versa. Slide 4
But depending on the conditions, two methods of vaporization are considered: evaporation and boiling. Today we will look at one of them - evaporation and its reverse process - condensation.
Teacher. What does the word “evaporate” the water from the bus window mean? How does the evaporation process occur? This is the phenomenon that we will consider today.
What do you guys think, what do all substances consist of?
Suggested answer: Substances are made up of molecules, molecules constantly move and interact.
Teacher. Do the molecules move at the same speeds?
Suggested answer: Molecules move at different speeds.
Teacher. What molecules leave the liquid?
Suggested answer: The fastest molecules leave the liquid.
Teacher: Can any “fast” molecules leave the liquid?
Suggested answer: In all likelihood, not all “fast” molecules can leave the liquid, but only those that are located at the surface of the liquid.
Teacher: Absolutely right, only those “fast” molecules can leave the liquid that are located at the surface of the liquid and that can overcome the attraction of neighboring molecules. The escaping molecules form vapor above the liquid.
What do you guys think, the speeds of the remaining molecules can change?
Suggested answer: The remaining molecules collide with other molecules as they move, causing their speed to change. Some molecules can gain enough speed to fly out of the liquid once they reach the surface.
Teacher: Let's conclude:
Evaporation is the formation of vapor that occurs from the surface of a liquid
The fastest molecules that leave the liquid are those that can overcome the attractive forces of neighboring molecules located at the surface of the liquid. (slide 5)
Teacher: We continue our exciting journey, the bus is rushing at high speed, and ahead of us is the station "Experiment". A beautiful building of the laboratory of physical sciences appeared. We get off the bus and head towards the building, the doors of the laboratory are hospitably open, we enter and in front of us is the world of science.
In front of us is a pavilion with the name “Find out what determines the rate of evaporation of liquid?”
To answer this question, small experimental studies need to be carried out.
Each table contains equipment and task cards. Carry out experiments and draw conclusions
(Work in pairs. Students complete tasks)
Exercise 1.
Task 2.
Task 3
Task 4.
Task 5.
3. Discussion of the results obtained
Teacher: We draw a conclusion. Show slide 6
Teacher: We continue our journey through the laboratory, the next pavilion "Condensation". What do you guys think, can the reverse process of vaporization occur, that is, can steam turn into liquid?
Blow on the glass that lies on your table. What did you see?
Suggested answer: Liquid droplets form on the glass.
Teacher: Where did these droplets of liquid come from?
Suggested answer: There is liquid vapor in the air and when it comes into contact with cold glass, the vapor turns into liquid.
Teacher: That's right, this process of turning steam into liquid is called condensation. Steam condensation is accompanied by the release of energy.
Show slide 7.
Teacher: Many beautiful natural phenomena are associated with the process of steam condensation. (explanation of the formation of clouds, fog, dew falling.) Their beauty and features are very well described in poetry.
“I saw it myself: An elephant was flying across the sky!
He swam importantly in the blue, even blocking out the sun!
...And again a miracle happened - he turned into a camel” (Poem by V. Lifshitz Cloud.)
And here are other lyrical poems by I. Bunin:
“The night is growing pale... A shroud of fog
In the hollows and meadows it becomes whiter,
Noisier forest, lifeless moon
And the silver of the dew on the glass is colder.”
Teacher: If the evaporation of a liquid occurs in a closed vessel, then the molecules will not only leave the liquid, but also return back to the liquid, and initially the number of molecules leaving the liquid will be greater than the number of molecules returning to the liquid - then such vapor above the liquid will be called unsaturated.
However, pretty soon the number of molecules flying out of the liquid will become equal to the number of vapor molecules returning back to the liquid. From this moment on, the number of vapor molecules above the liquid will be constant. The so-called dynamic equilibrium between vapor and liquid occurs. Such a pair is called saturated.
Show slide 8.
Teacher: now we will visit the pavilion "Evaporation in nature and technology"
Slide view 9.10
Teacher: And here is the pavilion "Solid your knowledge" How interesting it is here! Show slides 11, 12.
And now, guys, let’s hurry to our comfortable bus, our journey to the “Land of Knowledge” is coming to an end. Let's analyze together what we learned while traveling and how we added to our knowledge base?
What phenomena have we studied today?
Suggested answer: We studied the phenomena of evaporation and condensation.
Teacher: What else have we learned?
Suggested answer: We learned that evaporation is the formation of vapor from the surface of a liquid and it occurs at any temperature.
Teacher: What factors determine the rate of evaporation of liquids?
Teacher: Does the energy and temperature of the body change during evaporation and condensation, how does the body temperature change during this.
Teacher: Do these phenomena find application in nature and technology?
View slide 13. What else have we learned?
Answer: Conduct observations and experiments, put forward hypotheses to explain the results of the experiment.
Teacher: We achieved the goals of the lesson and completed the assigned tasks.
3. Working with the assessment sheet. Students tally their scores and grades on a sheet and give it to the teacher. The teacher comments and gives grades in the journal and diary.
Lesson marks: “5”: - 6
Teacher: Let's write down the homework: paragraph 16,17. exercise 9
Teacher: Our journey ends. I felt very comfortable in class with you guys today. I wish you success!
The lesson was taught and the lesson was developed by a physics teacher from the State Budget Educational Institution of Secondary School. Chetyrovka Kot Z. A.
Materials used when questioning, explaining and reinforcing a new topic.
Evaluation sheet:
1. Work with cards: ____ points
2. Work on definitions ___points (for each correct answer 1 point).
3.Evaluation of test No. 1: ______________ points.
(for each correct answer 1 point, each person receives it individually).
4. Assessment of problem solving at the board ________ points (from 2 to 5 points)
5. Evaluating work based on answers to questions: _______points.
(for each correct answer 1 point)
6. Evaluation of test No. 2: ________________ points
(for each correct answer 1 point)
Total: _________________ points. Grade: _________
Number of points from 14 points and above - score “5”
Number of points from 12 to 14 points - score “4”
Number of points from 9 to 12 points - score “3”
Task No. 1
How much energy must be expended to make ice weighing 20 kg? with an initial temperature of - 10ºC, melt and heat the resulting water
up to 100 ºC? (st = 4200 J./kg ºC, ۸ = 340∙10³ J/kg, sl = 2100 J./kg ºC)
Problem No. 2
Find the specific heat capacity of a substance weighing 5 kg from which the part is made if, when heated from 20 ºC to 120 ºC, it was given 230 kJ of heat.
Task No. 3
For melting a blank weighing 80 kg at the melting temperature
16800 kJ of energy was expended. Find the specific heat of fusion of the substance from which the blank is made and what kind of substance is it?
Answers to solving problems.
Task No. 1. Task No. 2.
Q= 16.62 106 J. s = 460 J/kg.ºС
Task No. 3
۸ = 2.1 105 J/kg.
Physics test: “Thermal phenomena.” No. 1
Option 1.
1. The metal part heated up when it was processed with a cutter. Can we say that a certain amount of heat is transferred to the part?
A. It is possible, since the internal energy of the part has increased. B. It is possible, since the internal energy of the part has decreased. IN.It is possible, since the internal energy of the part has not changed . G. It is impossible, since the internal energy of the part increased during work, and not during heat transfer. D. It is impossible, since the internal energy of the part increased during heat transfer, and not during work.
2. Cold water was poured into one glass, and hot water into the other. The mass of water in the glasses is the same. What can be said about the internal energy in glasses?
A. The internal energy of water in glasses is the same . B. The internal energy of water in the second glass is greater. IN.The internal energy of water in the first glass is greater. G. The internal energy of water in the first glass can be greater or less. D.Don't know.
3.Which of the bodies - solids, liquids or gases - have the least
thermal conductivity?
A. Solids. B. Liquids. IN.Gases. G. Solids and liquids.
D. Solids and gases.
4. The specific heat capacity of water is 4200 J/kg·ºc. How does the internal energy of 1 kg change? water when cooled by 1 ºС?
A. Increased by 4200 J. B. Decreased by 4200 J. IN. Hasn't changed.
D. Increased by 8400 J. G. Decreased by 8400 J.
5. Cast iron iron weighing 2 kg. heated from 20 ºС to 220 ºС. How much heat is needed to expend? (Specific heat capacity of cast iron 540 J / kg ºc.)
A. 216000J. B. 237600 J. IN. 259200 J. G.21600 J. D. None of the answers are correct.
Physics test: “Thermal phenomena” No. 1
Option 2
1. What is meant by the internal energy of the body?
A. The energy of movement and interaction of particles that make up the body.
B. Only the energy of motion of the particles that make up the body.
IN. Only the interaction energy of the particles that make up the body.
G. Kinetic energy of the body.
D. Potential and kinetic energy of the body.
2. A cold metal spoon was dipped into a glass of hot water.
Has the internal energy of the spoon changed? If yes, then how?
A. Increased by doing work. B. Decreased due to the work being done. IN. Hasn't changed. G. Decreased due to heat transfer. D. Increased due to heat transfer.
3. In what bodies can convection occur: in solids,
A. In solids. B. In liquids . IN. In gases. G. In solids and liquids. D. In liquids and gases.
4. Is the internal energy of 1 kg of ice and 1 kg of water, taken at the melting temperature (00 WITH)? A.Identical. B. The internal energy of ice is greater. IN. The internal energy of ice is less. G.The internal energy of ice can sometimes be greater and sometimes less. D. Don't know.
Physics test on the topic “Evaporation and Condensation” No. 2
Option 1.
1. The rate of evaporation of liquid depends on...
A. type of substance;
B. surface area of the liquid;
B. liquid temperature;
G. from the mass of the liquid;
D. A, B, C, correct;
E. all answers are incorrect.
2. Evaporation occurs when...
A. a constant certain temperature of the liquid;
B. any liquid temperature;
B. constant at any liquid temperature
3. During evaporation, the temperature of the steam...
A. greater than the temperature of the evaporating liquid;
B. less than the temperature of the evaporating liquid;
V. equal to the temperature of the evaporating liquid.
4. The energy of the generated steam...
A. more energy from evaporating water;
B. less energy from evaporating water;
V. is the same as the energy of evaporating water.
5. Do solids evaporate?
A. solids do not evaporate;
B. solids evaporate;
V. I don’t know.
6. The energy of the resulting liquid during condensation...
A. decreases;
B. increases;
B. Same.
Physics test on the topic “Evaporation and condensation” No. 2
Option 2.
1. Evaporation is the formation of vapor that occurs...
A. from the free surface of the liquid;
B. inside the liquid with the formation of bubbles;
B. throughout the entire volume of liquid.
2. During evaporation, the temperature of the liquid...
A. decreases;
B. increases;
G. remains unchanged.
3. The energy of the evaporating liquid...
A. decreases;
B. increases;
G. remains unchanged.
4. The dimensions of the molecules of the resulting vapor...
A. larger than the size of the molecules of evaporating water;
B. smaller than the size of the molecules of evaporating water;
A. are the same as the sizes of the molecules of evaporating water.
5. Condensation is the transition of matter...
A. from a gaseous state to a liquid state;
B. from solid to liquid;
V. from a liquid to a solid state;
G. from a liquid state to a gaseous state.
6 Saturated steam is steam located...
A.in dynamic equilibrium with its fluid;
B. is not in dynamic equilibrium with its fluid;
B. both answers are incorrect.
Key to tests on the topic “Thermal Phenomena”.
Option 1. Option 2.
1.A 1.A.
2.B. 2. D.
3.B. 3. D
4.B. 4. V.
5.A. 5 B.
6. a) 6; b) 2;3,c) 1;2 and 6;7. 6.B. a) 2; b) 5;6,c) 2;3 and 5;6.
“3” - 4 correct answers;
“2” -3 or less correct answers.
Key to tests on the topic "Evaporation and Condensation".
Option 1. Option 2.
1.D 1.A.
2.B. 2. A.
3.A. 3. A
4.A. 4. V.
5 B. 5.A.
6. A 6. A
Rating: “5” - 6 correct answers;
“4” - 5 correct answers;
"3" - 4 correct answers
“2” -3 or less correct answers.
Experimental tasks
Exercise 1. Equipment: thermometer, cotton wool, vessel with water. Record the thermometer readings. Wrap the thermometer ball with cotton wool moistened with water. How do thermometer readings change? Why?
Task 2. Equipment: 2 glass plates, pipette, vessel with nail polish remover, vessel with water. Using a pipette, drop a drop of water and nail polish remover onto the glass plates. Watch them evaporate. Make a conclusion about the rate of evaporation of liquids.
Task 3. Equipment: 2 glass plates, pipette, vessel with nail polish remover, electric lamp. Place a drop of liquid on the glass plates. Place one of the plates over an electric lamp. Draw a conclusion about the dependence of the evaporation rate on the temperature of the liquid.
Task 4. Equipment: 2 glass plates, pipette, vessel with nail polish remover, paper fan. Place a drop of liquid on the glass plates. Fan one of the plates. Draw a conclusion about the dependence of the rate of evaporation on the presence of wind.
Task 5. Equipment: 2 glass plates, pipette, container with nail polish remover. Place a drop of liquid on the plates. Distribute the drop on one of the plates so that it occupies the maximum area. Draw a conclusion about the dependence of the evaporation rate on the free surface area.
Experimental tasks. Exercise 1. Equipment: thermometer, cotton wool, vessel with water. Record the thermometer readings. Wrap the thermometer ball with cotton wool moistened with water. How do thermometer readings change? Why?
Task 2. Equipment: 2 glass plates, pipette, vessel with nail polish remover, vessel with water. Using a pipette, drop a drop of water and nail polish remover onto the glass plates. Watch them evaporate. Make a conclusion about the rate of evaporation of liquids.
Task 3. Equipment: 2 glass plates, pipette, vessel with nail polish remover, electric lamp. Place a drop of liquid on the glass plates. Place one of the plates over an electric lamp. Draw a conclusion about the dependence of the evaporation rate on the temperature of the liquid.
Task 4. Equipment: 2 glass plates, pipette, vessel with nail polish remover, paper fan. Place a drop of liquid on the glass plates. Fan one of the plates. Draw a conclusion about the dependence of the rate of evaporation on the presence of wind.
Task 5. Equipment: 2 glass plates, pipette, container with nail polish remover. Place a drop of liquid on the plates. Distribute the drop on one of the plates so that it occupies the maximum area. Draw a conclusion about the dependence of the evaporation rate on the free surface area.
Air"
1. Evaporation is..., occurs...
Boiling is..., happens...
Condensation is..., occurs...
a) the process of vaporization throughout the entire volume of liquid;
b) the process of vaporization from the surface of the liquid;
c) reverse boiling process;
d) reverse evaporation process;
e) the process of releasing dissolved gases and liquids;
f) at any positive temperature;
g) at the temperature specified for the liquid;
h) the process of transition of a substance from the gaseous phase to the liquid phase.
1) h g, a g, d f; 2) h f, a g, h g; 3) h f, a g, c g; 4) h g, a f, c f.
2. The boiling point of the liquid...
Liquid evaporation temperature...
Liquid condensation temperature...
a) will increase with increasing atmospheric pressure;
b) will decrease with increasing atmospheric pressure;
c) does not depend on atmospheric pressure.
1) a with a; 2) aba; 3) a a a; 4) bс с.
3. The intensity of the evaporation process depends... at the same time...
a) on the free surface area;
b) on the temperature of the liquid;
d) depending on the type of liquid;
e) on the ambient temperature;
f) on the magnitude of the Archimedean force;
g) from hydrostatic pressure;
h) from external pressure;
i) the temperature of the liquid remains unchanged; j) the temperature of the liquid increases; k) the temperature of the liquid decreases.
1) a d e f h, l; 2) g e f h, l; 3) a g e g h, i; 4) g g h, i; 5) a b c d, k; 6) a in d, and; 7) a c d, and; 8) a b, i.
4. Relative humidity 100%. Compare the readings of the T1 wet bulb and T2 dry bulb psychrometers.
a) T1 = T2; b) T1 >T2; c) T1< Т2; d) ответ неоднозначный.
5. How does the absolute humidity of air change when it is heated in a closed vessel?
6. How will the relative humidity of the air change when it is cooled in a closed vessel?
a) will increase; b) will decrease; c) will remain constant.
7. The elasticity of water vapor at 20 °C is 2 kPa. What will the absolute humidity be when the temperature drops to 10 °C?
a) 4 kPa; b) 3 kPa; c) 2 kPa; d) 1 kPa.
8. What will be the relative humidity of the air after the temperature decreases (see the condition of the previous problem), if p0(10 °C) = 1.22 kPa.
a) 80%; b) 82%; c) 70%; d) 72%.
9. How will the pressure of saturated steam change when its volume decreases (increases)?
a) will increase; b) will decrease; c) will not change.
10. Which of the graphs correctly shows the dependence of saturated vapor pressure on absolute temperature?
A) by 1; B) by 2; C) by 3; D) by 4.
11. Look at the drawing
11.1. At what part of the isotherm of real steam does the transformation of steam into liquid occur?
a) 1-2; b) 2-3; c) 3-4; d) such a process does not occur.
11.2. How can you convert unsaturated steam into saturated steam (rev. problem):
a) reduce the volume and temperature; b) increase volume and temperature;
c) reduce the volume and increase the temperature; d) increase the volume and decrease the temperature.
11.3. Which branch corresponds to:
1) liquids; 2) gas; 3) two-phase “liquid-vapor” state.
a) 2-3; 1-2; 3-4; b) 3-4; 1-2; 2-3; c) 3-4; 2-3; 1-2; d) 1-2; 2-3; 3-4.
*12. Determine the absolute and relative humidity at a temperature of 20 °C if the dew point is 10 °C. The saturated vapor pressures are respectively p01(20 °C) = 2.33 kPa and p02(10 °C) = 1.22 kPa.
a) 1.22 kPa: 48%; b) 2.33 kPa: 48%; c) 1.22 kPa: 52%; d) 2.33 kPa: 52%.
*13. The pressure of water vapor in the atmosphere at 20 °C is 1.6 kPa. Will dew fall if the air temperature drops to 15 °C at night; р0(15 °С) – 1.72 kPa.
a) falls out; b) will not fall out; c) the answer is ambiguous.
Evaporation- vaporization that occurs at any temperature from the free surface of the liquid. The uneven distribution of kinetic energy of thermal motion of molecules leads to the fact that at any temperature the kinetic energy of some molecules of a liquid or solid may exceed the potential energy of their connection with other molecules. Molecules with greater speed have greater kinetic energy, and body temperature depends on speed
the movement of its molecules, therefore, evaporation is accompanied by cooling of the liquid. The rate of evaporation depends on: the open surface area, temperature, and the concentration of molecules near the liquid. Condensation- the process of transition of a substance from a gaseous state to a liquid state.
The evaporation of a liquid in a closed vessel at a constant temperature leads to a gradual increase in the concentration of molecules of the evaporating substance in the gaseous state. Some time after the start of evaporation, the concentration of the substance in the gaseous state will reach a value at which the number of molecules returning to the liquid becomes equal to the number of molecules leaving the liquid during the same time. Installed dynamic equilibrium between the processes of evaporation and condensation of matter. A substance in a gaseous state that is in dynamic equilibrium with a liquid is called saturated steam. (Ferry are the collection of molecules that left the liquid during the evaporation process.) Vapor located at a pressure below saturated is called unsaturated.
Due to the constant evaporation of water from the surfaces of reservoirs, soil and vegetation, as well as the respiration of humans and animals, the atmosphere always contains water vapor. Therefore, atmospheric pressure is the sum of the pressure of dry air and the water vapor contained in it. The water vapor pressure will be maximum when the air is saturated with steam. Saturated steam, unlike unsaturated steam, does not obey the laws of an ideal gas. Thus, saturated vapor pressure does not depend on volume, but depends on temperature. This dependence cannot be expressed by a simple formula, therefore, based on an experimental study of the dependence of saturated vapor pressure on temperature, tables have been compiled from which its pressure can be determined at different temperatures.
The pressure of water vapor in the air at a given temperature is called absolute humidity, or the elasticity of water vapor. Since vapor pressure is proportional to the concentration of molecules, absolute humidity can be defined as the density of water vapor present in the air at a given temperature, expressed in kilograms per cubic meter ( R).
Most of the phenomena observed in nature, for example, the rate of evaporation, the drying out of various substances, and the wilting of plants, depend not on the amount of water vapor in the air, but on how close this amount is to saturation, i.e. relative humidity, which characterizes the degree of saturation of air with water vapor.
At low temperatures and high humidity, heat transfer increases and a person becomes hypothermic. At high temperatures and humidity, heat transfer, on the contrary, is sharply reduced, which leads to overheating of the body. The most favorable for humans in middle climatic latitudes is a relative humidity of 40-60%. Relative humidity is the ratio of the density of water vapor (or pressure) in the air at a given temperature to the density (or pressure) of water vapor at the same temperature, expressed as a percentage, i.e. = p/p 0 100%, or ( p = p/p 0 100%.
Relative humidity varies widely. Moreover, the daily variation of relative humidity is the opposite of the daily variation of temperature. During the day, with increasing temperature, and therefore with increasing saturation pressure, relative humidity decreases, and at night it increases. The same amount of water vapor can either saturate or not saturate the air. By lowering the air temperature, the steam in it can be brought to saturation. dew point is the temperature at which vapor in the air becomes saturated. When the dew point is reached in the air or on objects with which it comes into contact, water vapor begins to condense. To determine air humidity, instruments called hygrometers And psychrometers.
Ticket No. 10
Crystalline and amorphous bodies. Elastic and plastic deformations of solids.
Response plan
1. Solids. 2. Crystalline bodies. 3. Mono- and polycrystals. 4. Amorphous bodies. .5. Elasticity. 6. Plasticity.
Everyone can easily divide bodies into solid and liquid. However, this division will only be based on external signs. In order to find out what properties solids have, we will heat them. Some bodies will begin to burn (wood, coal) - these are organic substances. Others will soften (resin) even at low temperatures - these are amorphous. Still others will change their state when heated as shown in the graph (Fig. 12). These are crystalline bodies. This behavior of crystalline bodies when heated is explained by their internal structure. Crystal bodies- these are bodies whose atoms and molecules are arranged in a certain order, and this order is preserved over a fairly large distance. The spatial periodic arrangement of atoms or ions in a crystal is called crystal lattice. The points of the crystal lattice at which atoms or ions are located are called nodes crystal lattice.
Crystalline bodies are either single crystals or polycrystals. Monocrystal has a single crystal lattice throughout its entire volume.
Anisotropy single crystals lies in the dependence of their physical properties on direction. Polycrystal It is a combination of small, differently oriented single crystals (grains) and does not have anisotropy of properties.
Most solids have a polycrystalline structure (minerals, alloys, ceramics).
The main properties of crystalline bodies are: certainty of melting point, elasticity, strength, dependence of properties on the order of arrangement of atoms, i.e., on the type of crystal lattice.
Amorphous are substances that have no order in the arrangement of atoms and molecules throughout the entire volume of this substance. Unlike crystalline substances, amorphous substances isotropic. This means that the properties are the same in all directions. The transition from an amorphous state to a liquid occurs gradually; there is no specific melting point. Amorphous bodies do not have elasticity, they are plastic. Various substances are in an amorphous state: glass, resins, plastics, etc.
Elasticity- the property of bodies to restore their shape and volume after the cessation of external forces or other reasons that caused the deformation of bodies. For elastic deformations, Hooke’s law is valid, according to which elastic deformations are directly proportional to the external influences causing them, where is mechanical stress,
Relative elongation, − absolute elongation E - Young's modulus (modulus of elasticity). Elasticity is due to the interaction and thermal movement of the particles that make up the substance.
Hooke's law −
Mechanical stress −
Plastic- the property of solids under the influence of external forces to change their shape and size without collapsing and to retain residual deformations after the action of these forces ceases.
Ticket number 11
Work in thermodynamics. Internal energy. First law of thermodynamics. Application of the first law to isoprocesses. Adiabatic process.
1. Vaporization –
A) the process of transition of a substance from a gaseous state to a liquid state;
B) the process of transition of a substance from a liquid to a gaseous state;
C) the process of transition of a substance from a liquid to a solid state.
2.
A) on the free surface area; B) on the temperature of the liquid;
B) from the presence of ventilation; D) depending on the type of liquid;
D) on the ambient temperature; E) on the magnitude of the Archimedean force.
3. Boiling point
A) will increase with increasing atmospheric pressure; B) will decrease with increasing atmospheric pressure;
B) does not depend on atmospheric pressure.
4. Saturated steam is
A) steam in dynamic equilibrium with its liquid;
B) steam formed over a boiling liquid;
C) vapor that is not in dynamic equilibrium with its liquid.
5. Saturated steam pressure
6.
7. Relative humidity 100%. Compare wet readingsT 1 and dry bulb thermometers T 2 psychrometers.
A) T 1 = T 2 ; B) T 1 >T 2 ; IN) T 1 < T 2 .
8. The partial pressure of water vapor in air at 19 o C was 1.1 kPa. What is the relative humidity of the air?
A) 64%; B) 50%; B) 70%; D) 98%.
10. What is the relative humidity in the room at a temperature of 16 o C, if dew forms at 10 o C?
Option No. 2
1.Types of vaporization:
A) condensation; B) evaporation; B) convection; D) boiling.
2. Evaporation is
A) the process of vaporization throughout the entire volume of liquid; B) the process of vaporization from the surface of a liquid; B) the reverse boiling process; D) the process of transition of a substance from the gaseous phase to the liquid phase.
3.
A) the temperature of the liquid remains unchanged; B) the temperature of the liquid increases;
C) the temperature of the liquid decreases.
4. Boiling point is
A) the temperature at which the saturated vapor pressure in the bubbles is equal to atmospheric pressure;
B) the temperature at which the saturated vapor pressure in the bubbles is equal to the pressure in the liquid;
C) the temperature at which the saturated vapor pressure in the bubbles equals the hydrostatic pressure.
A) depending on the type of liquid; B) from atmospheric pressure; B) on the ambient temperature; D) from ventilation.
6.
A) will increase; B) will decrease; B) will not change.
A) depends on the volume it occupies; B) does not depend on the volume it occupies.
8. Relative air humidity is
A) a value indicating the quantitative content of water vapor in the air;
B) a value showing how close water vapor is to saturation at a given temperature;
B) a value indicating the presence of water vapor in the atmosphere.
9. The wet thermometer of the psychrometer shows 10 o C, and the dry thermometer shows 14 o C. What is the relative humidity?
A) 30%; B) 40%; B) 50%; D) 60%.
10. What is the relative humidity in the room at 18 o C, if dew forms at 10 o C?
A) 42%; B) 59%; B) 62%; D) 84%.
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Test on the topics “Mutual transformations of liquids and gases”
Option #1
1. Vaporization -
A) the process of transition of a substance from a gaseous state to a liquid state;
B) the process of transition of a substance from a liquid to a gaseous state;
C) the process of transition of a substance from a liquid to a solid state.
2. The intensity of the evaporation process depends
A) on the free surface area; B) on the temperature of the liquid;
B) from the presence of ventilation; D) depending on the type of liquid;
D) on the ambient temperature; E) on the magnitude of the Archimedean force.
3. Boiling point
A) will increase with increasing atmospheric pressure; B) will decrease with increasing atmospheric pressure;
B) does not depend on atmospheric pressure.
4. Saturated steam is
A) steam in dynamic equilibrium with its liquid;
B) steam formed over a boiling liquid;
C) vapor that is not in dynamic equilibrium with its liquid.
5. Saturated steam pressure
6. How does the density of saturated vapor change as its volume increases?
7. Relative humidity 100%. Compare wet readings T 1 and dry bulb thermometers T 2 psychrometers.
A) T 1 = T 2; B) T 1 >T 2; B) T 1< Т 2 .
8. Partial pressure of water vapor in air at 19 O C was 1.1 kPa. What is the relative humidity of the air?
A) 64%; B) 50%; B) 70%; D) 98%.
10. What is the relative humidity in the room at a temperature of 16 o C, if at 10 o Does dew form?
Test on the topics “Mutual transformations of liquids and gases”
Option No. 2
1.Types of vaporization:
A) condensation; B) evaporation; B) convection; D) boiling.
2. Evaporation is
A) the process of vaporization throughout the entire volume of liquid; B) the process of vaporization from the surface of a liquid; B) the reverse boiling process; G)the process of transition of a substance from the gaseous phase to the liquid phase.
3. Liquid temperature during evaporation
A) the temperature of the liquid remains unchanged; B) the temperature of the liquid increases;
C) the temperature of the liquid decreases.
4. Boiling point is
A) the temperature at which the saturated vapor pressure in the bubbles is equal to atmospheric pressure;
B) the temperature at which the saturated vapor pressure in the bubbles is equal to the pressure in the liquid;
C) the temperature at which the saturated vapor pressure in the bubbles equals the hydrostatic pressure.
5. The temperature of a liquid at boiling depends on
A) depending on the type of liquid; B) from atmospheric pressure; B) on the ambient temperature; D) from ventilation.
6. How does the pressure of saturated vapor change as its volume decreases?
A) will increase; B) will decrease; B) will not change.
7. Saturated vapor density
A) depends on the volume it occupies; B) does not depend on the volume it occupies.
8. Relative air humidity is
A) a value indicating the quantitative content of water vapor in the air;
B) a value showing how close water vapor is to saturation at a given temperature;
B) a value indicating the presence of water vapor in the atmosphere.
9. The wet bulb of the psychrometer shows 10 o C, and dry 14 o C. What is the relative humidity?
A) 30%; B) 40%; B) 50%; D) 60%.
10. What is the relative humidity in the room at 18 o C, if at 10 o Does dew form?
A) 42%; B) 59%; B) 62%; D) 84%.
Option 1.
1. Above the sea surface at a temperature of 250C, the relative air humidity turned out to be
equal to 95%. At what temperature can you expect fog to appear?
2. In a room with a volume of 40 m3, the air temperature is 200C, its relative humidity is 20%.
How much water must be evaporated for the relative humidity to reach 50%? It is known
that at 200C the saturated vapor pressure is 2330 Pa.
3. The partial pressure of water vapor in the room is 2⋅103 Pa, and the saturated pressure
water vapor at the same temperature is 4⋅103 Pa. What is relative
air humidity in the room?
4. A pot of water, covered with a lid, was placed on a gas stove. If you remove it from the pot
lid, the water will take longer to heat to boil than if it had remained covered. This
the fact is explained by the fact that
1) without a lid, the saturated vapor pressure in the bubbles should be higher due to the influence
atmosphere
2) under the lid the air and steam pressure above the water surface is higher
3) without a lid, heat transfer from water to the surrounding air increases
4) the lid is metal, so it improves the heat exchange of water with the atmosphere
air
5. In a cubic meter of air in a room at a temperature of 20°C there is 1.12⋅10–2 kg
water vapor. Using the table of density of saturated water vapor, determine
relative air humidity.
16
17
18
19
20
21
22
23
24
g/m3
1,36
1,45
1,54
1,63
1,73
1,83
1,94
2,06
2,18
6. Two vessels with volumes of 20 l and 30 l, connected by a tube with a tap, contain wet
air at room temperature. The relative humidity in the vessels is
30% and 40% respectively. If the tap is opened, what will be the relative
air humidity in the vessels after thermal equilibrium has been established, counting
constant temperature?
7. The relative air humidity in a closed vessel with a piston is 40%.
Determine the relative humidity if the volume of the vessel due to the movement of the piston
at a constant temperature, reduce by 3 times.
Test on the topic “Saturated steam. Humidity."
Option 2.
1. Partial pressure of water vapor at a temperature of 40 ° C and relative humidity
80% is equal to 4.8 kPa. What is the pressure of saturated water vapor at this temperature?
2. Relative air humidity at t = 360 C is 80%. Saturation pressure
steam at this temperature p0 = 5945 Pa. What mass of steam is contained in 1m3 of this air?
3. Relative humidity in a closed vessel is 30%. What will the relative
humidity if the volume of the vessel at a constant temperature is reduced by 2 times?
4. Relative humidity in the room at a temperature of 20 ° C
equal to 70%. Using the table of saturated vapor pressure of water, determine the pressure
water vapor in the room.
t, °С
16
17
18
19
20
21
22
23
24
25
r, mmHg Art.
13,6
14,5
15,5
16,5
17,5
18,7
19,8
21,1
22,4
23,8
5. A vessel divided by a partition into two equal parts contains moist air.
The temperature and air pressure in both parts of the vessel are the same. Its relative
the humidity in one half of the vessel is 20%, and in the other - 80%. What will the humidity be like?
6. The relative air humidity in a closed vessel with a piston is 40%. Volume
In the final state, the volume of the vessel is 4 times less than the initial one. Choose from the offer
list two statements that correspond to the results of the conducted
experimental observations, and indicate their numbers.
1) When the volume of the vessel decreases by 2.5 times, dew appears on the walls.
2) The vapor pressure in the vessel increases all the time.
3) In the final and initial states, the mass of steam in the vessel is the same.
4) When the volume was reduced by 2 times, the relative humidity of the air in the vessel became equal to
80%.
5) In the final state, all the vapor in the vessel has condensed.
7. The partial pressure of water vapor in the room is 2.5 times less than the saturated pressure
water vapor at the same temperature. Determine the relative air humidity in
room.
Problems on the topic “Saturated steam. Humidity".
1. There is a wide pan of water on the gas stove, covered with a lid. If water from it
pour into a narrow saucepan, the water will boil noticeably longer than if it had remained in
wide. The main reason for this is that
1) the surface area of the water decreases and, therefore, evaporation occurs less actively
2)
the heating area decreases and, therefore, the heating rate decreases
water
3)
the depth of the water layer increases noticeably and, therefore, the water warms up less
evenly
4)
the required saturated vapor pressure in the bubbles increases significantly and,
therefore, the water at the bottom heats up to a higher temperature
2. Relative humidity in the room is 70%, partial pressure
water vapor 13.9 mm Hg. Art. Using the saturated pressure table below
water vapor at different temperatures, determine the air temperature in the room.
t, °С
16
17
18
19
20
21
22
23
24
25
r, mmHg Art.
13,6
14,5
15,5
16,5
17,5
18,7
19,8
21,1
22,4
23,8
1) 16 °C
2) 17 °C
3) 22 °C
4) 25 °C
3. Relative humidity in the room is 60%, partial pressure
water vapor 8.7 mm Hg. Art. Using the saturated pressure table below
water vapor, determine the air temperature in the room.
t, °С
16
17
18
19
20
21
22
23
24
25
r, mmHg Art.
13,6
14,5
15,5
16,5
17,5
18,7
19,8
21,1
22,4
23,8
1) 16 °C
2) 17 °C
3) 22 °C
4) 25 °C
4. The relative humidity in a closed vessel with a piston is 40%. Define
relative humidity, if the volume of the vessel due to the movement of the piston at a constant
reduce temperature by 3 times.
5. The cylinder under the piston contains liquid and its saturated vapor. How will they change
vapor pressure and liquid mass when the piston moves slowly downward at constant
temperature until the piston touches the surface of the liquid?
For each quantity, determine the corresponding nature of the change:
1)
2)
3)
increases
decreases
does not change
Write down the selected numbers for each physical quantity in the table. Numbers in the answer
may be repeated.
Steam pressure
6. A glass vessel containing humid air at t1=30 °C was tightly closed with a lid and
heated to t2=50 °C. Based on the laws of molecular physics, explain how the
at the same time, the partial pressure of water vapor and the relative humidity of the air in the vessel.
Liquid mass
7. At the same temperature, saturated ammonia vapor in a closed vessel differs from
unsaturated steam
1) concentration of molecules
2) the average speed of the chaotic movement of molecules
3) the average energy of the chaotic movement of molecules
4) absence of foreign gases
8. Which of these statements is(are) correct?
A. lower the temperature of the steam at a constant volume and number of molecules.
B. increase the concentration of vapor molecules at a constant temperature.
1) only A
2) only B
3) both A and B
4) neither A nor B
9. Which of the statements is(are) correct?
Unsaturated steam can be made saturated if
A. cool the steam at a constant volume and number of molecules.
B. compress steam at a constant number of its molecules and temperature.
1) only A
2) only B
3) both A and B
4) neither A nor B
10. Relative air humidity at a temperature of 100 oC is 70%. Define
partial pressure of water vapor contained in the air.
11. On Monday and Tuesday the air temperature was the same. Partial pressure
There was less water vapor in the atmosphere on Monday than on Tuesday.
From the list below, select two correct statements and indicate their numbers.
1) The mass of water vapor contained in 1 m3 of air on Monday was greater than on Tuesday
2) Relative humidity on Monday was lower than on Tuesday
3) The concentration of water vapor molecules in the air on Monday and Tuesday was the same
4) The pressure of saturated water vapor on Monday was higher than on Tuesday
5) The density of water vapor contained in the air on Monday was less than on Tuesday
12. The partial pressure of water vapor in the room is 2.5 times less than the saturated pressure
water vapor at the same temperature. Determine the relative humidity in the room.
13. The relative humidity of the air in a closed vessel under the piston is 40%. What will it be
relative humidity of the air in the vessel, if its volume due to the movement of the piston at
increase by 2 times at constant temperature?
14. The relative humidity of the air in a vessel closed with a piston is 40%. What will it become
relative humidity of the air in the vessel, if its volume is at a constant temperature
reduce by 2 times?
15. In the air of a school classroom at a relative humidity of 20%, the partial pressure
water vapor is 800 Pa. Determine the pressure of saturated water vapor at a given
temperature.
16. In a room measuring 4x5x3 m, in which the air has a temperature of 10 °C and a relative
humidity 30%, turned on a humidifier with a capacity of 0.2 l/h. What will happen
What is the relative humidity in the room after 1.5 hours? Saturation pressure
water vapor at a temperature of 10 °C is equal to 1.23 kPa. Consider the room to be a sealed vessel.
17. A vessel divided by a partition into two equal parts is filled with air. In one part
The vessel contains dry air, and the other contains humid air, its relative humidity is 50%.
The temperature and air pressure in both parts of the vessel are the same. What will the humidity be like?
air in the vessel if the partition is removed?
18. The relative air humidity in a closed vessel with a piston is 50%. Volume
Due to the movement of the piston, the pressure of the vessel is slowly reduced at a constant temperature. IN
In the final state, the volume of the vessel is 4 times less than the initial one. Choose from
of the proposed list, two statements that correspond to the results
experimental observations carried out, and indicate their numbers.
1) The vapor density in the vessel increases all the time.
2) The steam pressure first increases and then remains constant.
3) In the final state, all the vapor in the vessel has condensed.
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