Vaporization and liquefaction
Vaporization: the change of a substance from one state to another. Vaporization requires heat. There are two ways to vaporize.
Liquefaction: The change of a substance from one state to another. It will after liquefaction.
(1) evaporation
1. Evaporation
The vaporization phenomenon that occurs in … is called evaporation.
2. Factors affecting evaporation rate:
(1) The temperature of the liquid. The higher the temperature of the liquid, the more evaporation; The lower the temperature of the liquid, the more it evaporates. The same wet clothes are dry in the sun and in the shade.
(2) The surface area of the liquid. The larger the surface area of the liquid, the more it evaporates; The smaller the surface area of a liquid, the more it evaporates. The same amount of water is dried in a plate and in a bottle.
(3) Air flow on the liquid surface. The faster the airflow on the liquid surface evaporates; The slower the air flows on the liquid surface, the more it evaporates. The same wet shoes are dried in ventilated and windless places.
3. Evaporative refrigeration: When the liquid evaporates, it needs the heat of the surrounding objects (or itself) to raise the temperature of the surrounding objects (or itself) and evaporate. The household refrigerator uses the freon that enters into the thin tube of the freezing chamber to evaporate quickly, so as to achieve the purpose of refrigeration.
(2) boiling
1. boiling
Boiling is a way of vaporization, which is a violent vaporization phenomenon that occurs simultaneously in a liquid at a certain temperature. In the experiment, we can find the boiling temperature, which is called. Boiling points of different liquids.
2. Two necessary conditions for liquid boiling: one is the temperature of the liquid, and the other is. Only when the above two conditions are met at the same time can the liquid reach boiling. If the temperature of the liquid reaches the boiling point and it can't continue to absorb heat, then the liquid also boils.
3. Similarities and differences between evaporation and boiling:
(1) Similarity:.
(2) Difference:
A. Evaporation is a vaporization phenomenon that only occurs, while boiling is a violent vaporization phenomenon that occurs at the same time as liquid;
B. Evaporation can occur at ambient temperature, while boiling occurs at ambient temperature;
C. When the liquid evaporates, it needs to absorb heat, and the temperature may decrease; Although the boiling process absorbs heat, the temperature remains unchanged;
D. the heat absorbed by evaporation mainly comes from the liquid itself, so evaporation is effective, and the heat needed for boiling comes from.
③ Liquefaction
1. Liquefaction and vaporization are two opposite processes, and substances are called liquefaction. For example, it is a phenomenon that water vapor turns into water.
2. Two methods of liquefaction: one is that gas can be liquefied; Second, gas can be liquefied.
Note: Some gases must be liquefied by two methods at the same time to achieve the purpose of liquefaction.
When gas is liquefied, it will release heat.
Why is it more serious to be burned by steam at 100℃ than by water at 100℃?
[Example 1] The following statement about evaporation is correct []
A. When the temperature is high, the liquid will evaporate quickly. Liquid can't evaporate until it absorbs heat.
C.0℃ water can also be evaporated. D. liquid can only evaporate at room temperature.
[Example 2] Among the following phenomena, [] does not belong to vaporization.
A. Fresh Chinese cabbage will wither slowly. B. Popsicles will turn white when they are taken out of the refrigerator.
C. Wet and dry clothes D. Alcohol will soon dry on the skin.
Example 3 Two students, A and B, each poured a cup of hot water with the same quality and temperature. A student blows water with his mouth, and B student pours water back and forth with two cups. After a while, the hot water stopped scalding his mouth. Their function of rapidly cooling water is []
A. blow with your mouth. Pour two glasses of water back and forth
C. is as fast as d. uncertain
[Example 4] A beaker filled with water is heated with an alcohol lamp to make the water in the beaker boil. A test tube filled with water is inserted into the beaker, and the water in the test tube will be [].
A. they can't reach the boiling point and can't boil.
B. Both can reach the boiling point, and both can boil.
C. all can reach the boiling point, but they cannot boil.
D. the heating time is a little longer and it can be boiled.
[Example 5] In the Guinness Book of World Records, it was recorded that barefoot walked about 7.5 meters on a burning charcoal pile at 650℃. He created this miracle, and the following statement is correct []
A. The performer must have put a high-grade heat insulation protective agent under his feet in advance.
B: The performer must have jumped over, so the contact time was short and the charcoal fire didn't have time to burn his feet.
C. The performer must have stepped on the charcoal fire with sweaty feet and walked easily step by step.
D. the performer must have tiptoed past, so the contact area was very small, even if the burns were not serious.
Put the cold boiled water in the clay pot, and after a while, you can drink cold drinks. What is the reason?
[Example 7] Xiaoming cooked the egg twice. The first time, after the water was boiled, he continued to cook it with strong fire until it was cooked. The second time, after the water is boiled, turn down the flame, but still keep the water in the pot boiling until it is cooked. Two comparisons found that []
A. Compared with the second method, the first method saves fuel and time.
B. The first method consumes fuel but saves time.
C. The second method saves fuel, but it takes more time than the first method.
D. the second method is more fuel-efficient than the first method, and the two methods take about the same time.
[Example 8] When the wrapping paper of popsicles is opened in summer, you can often see that popsicles are emitting "white gas" because []
A. small water droplets produced by melting popsicles
B. When the popsicle is released after cooling, water droplets are formed by the liquefaction of surrounding water vapor.
C. the air around the popsicle will be liquefied when it is cold.
D. the water vapor generated by evaporation after the popsicle melts.
The fuel of the gas lighter is butane gas, which was put into the lighter by _ _ _ _ _.
Simulated test questions (answer time: 50 minutes)
(a) fill in the blanks
1. Wet clothes will dry after airing for a period of time, which is actually the _ _ _ _ process of water and one of the _ _ _ _ phenomena of material state change, and can be carried out at the temperature of _ _ _ _.
Because of the wind, people will feel very cool when they come ashore from the swimming pool. This is because of _ _ _ _ _ _ _ _ _ _ _
3. A large number of facts show that liquid evaporation needs _ _ _ _ heat, so evaporation has _ _ _ _ effect.
4. The phenomenon that a substance changes from a liquid state to a _ _ _ _ state is called vaporization. There are two forms of vaporization: _ _ and _ _ _ _.
5. Boiling is a violent vaporization phenomenon. At the temperature of _ _ _ _ _, liquid and liquid occur at the same time. In the process of boiling, the liquid needs _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.
6. The phenomenon observed during boiling is that _ _ _ _ _ _ _ is formed in water, and reaches the surface of _ _ _ _ _ _ when it rises, and the water vapor inside is emitted into the air.
7. In the process of boiling, the liquid will keep _ _ _ _ _ hot, but the temperature will keep _ _ _ _ _. This temperature is called the boiling point, and the boiling points of different substances are _ _ _ _ _ _ _ (please fill in "same" and "different").
8. Put some water that has just stopped boiling in the flask, and then pump the air out of the flask with an air pump. At this time, the air pressure on the water surface is _ _ _ _ (select "decrease", "unchanged" or "increase"), and it can be observed that the water in the flask is boiling again. It can be seen that the air pressure above the liquid level can reduce the boiling point of water.
9. The refrigerator is made according to the principle that _ _ _ heat is generated when the substance is vaporized and _ _ _ heat is generated when it is liquefied.
10. _ _ _ _ _ and _ _ _ are two methods of liquefying gas. Liquefied petroleum gas is realized by _ _ _ _ _.
1 1. When I opened the refrigerator door, I saw "white gas". This "white gas" is _ _ _ _ _, which is caused by _ _ _ _ _.
12. People are burned more seriously by steam at 100℃ than by boiling water at 100℃ because _ _ _ _.
13. In winter in the north, drivers often use a mixture of water and alcohol as the coolant of the automobile cooling system, because this mixture contains _ _ _ _ _.
14. When cooking and frying food, it is often seen that after splashing a drop of water in a boiling oil pan, it will make a violent noise and the oil will be spilled. The main reason is _ _ _ _.
15. When a doctor examines a patient's teeth, he will burn a "small mirror with a handle" on an alcohol lamp and put it in the patient's mouth. The purpose of this is _ _ _ _.
(2) Multiple choice questions
1. There are two containers, A and B, which contain alcohol with the same quality and temperature respectively. After a while, ()
A. there is more alcohol in container a.
C.there are as many as two containers. This is impossible to judge.
When swimming in summer, you don't feel cold in the water, but when you go ashore, you feel cold. This is because ()
A. the temperature of water is high and the temperature of air is low.
B.air conducts heat more easily than water.
C. the evaporation of water on the human surface should absorb heat.
D. none of the above is true
Blowing with an electric fan in summer makes people feel cool. This is because ()
A. the wind energy blown by the electric fan produces cold air.
B. the wind energy blown by the electric fan reduces the temperature of the air.
C. the wind energy blown by the electric fan absorbs the heat of human body.
D the wind energy blown by the electric fan accelerates the evaporation of water on the surface of human body.
4. The boiling point of benzene at 1 atmospheric pressure is11℃. If the temperature of toluene at 1atm is 1 1℃, the following statement is correct ().
A. toluene will not boil.
C. Toluene will boil if it continues to absorb heat. D. None of the above statements are correct.
As shown in the figure, both the big container A and the small container B are filled with water. The heating at the bottom of container A makes the water in container A boil, and the water in container B () continues to heat.
A. You can't boil until you reach the boiling point. B. You can reach the boiling point, but you can't boil.
C. it can not reach the boiling point, but it can boil. D. it can reach the boiling point and boil.
6. Boil the water with a kettle, and then continue to heat it with strong fire, so that the temperature of the water will be ().
A. gradually increase B. unchanged C. gradually decrease D.
7. Fog and dew are formed by water vapor in the air. ( )
A. melting B. vaporizing C. liquefying D. curing
8. In general, it is known that the boiling point of liquid oxygen is-183℃, that of liquid nitrogen is-196℃ and that of liquid helium is -268.9℃. These gases are extracted by liquid air, and the order of separation with the increase of temperature is ().
A. oxygen, helium and nitrogen B. oxygen, nitrogen and helium C. helium, oxygen and nitrogen D. helium, nitrogen and oxygen
9. There are often sayings in life that "the soup is not boiled" and "the bottom is drawn". To raise soup and stop boiling is to scoop up the boiling water in the pot and dump it. Cutting firewood at the bottom of the pot is cutting burning wood from the bottom of the pot. Applying thermal knowledge to analyze the following statement is correct ()
A. Whether it is "raising the soup to stop boiling" or "taking the bottom out of the pot", it can only stop boiling temporarily.
B. whether it is "raising the soup to stop boiling" or "taking the bottom out of the pot", it can completely stop boiling.
C. "Raise the soup to stop boiling" can only stop boiling temporarily, and "withdraw the salary from the bottom of the pot" can completely stop boiling.
D. "Raise the soup to stop boiling" can completely stop boiling, and "take a salary from the bottom of the pot" can only stop boiling temporarily.
10. When I wake up in the late autumn morning, I can see many small water drops on the window of my room, especially at ().
A. the side of the window glass facing the room
C. the inside and outside of the window glass D. which side is uncertain
1 1. Food is usually stewed in a bowl (the bowl does not touch the pot). When the water in the pot boils, the soup in the bowl ().
A.it will boil slowly. B.it will boil at the same time.
C. it will not boil at 100℃. D. it will not boil below 100℃.
12. When the pot is heated and the water inside continues to boil, the "white gas" on the water surface is not obvious; If the fire suddenly stops, there will be a lot of "white gas" on the water soon, because ()
A. water does not evaporate when it boils.
B. When boiling, the water vapor is higher than 100℃.
C. after the fire was put out, a lot of water began to evaporate.
D the water surface temperature after fire extinguishing is lower than 100℃; A large amount of water vapor is liquefied into small water droplets, forming "white gas"
13. In summer, someone wrapped a wet towel outside the bottle, hoping that the milk would not go bad soon. From a physical point of view, this practice ()
Answer is meaningless, because heat transfer will not occur when the temperature between objects is the same.
B. Wrong. Wet towel bags make it difficult for the bottle to dissipate heat, but the milk will go bad.
C. Correct, the water in the wet towel has evaporated, so it is necessary to absorb some heat from the bottle, which has a cooling effect, thus delaying the deterioration of milk.
(3) Inference questions
1. In hot summer, sprinkling some water inside the house will make you feel cool, while sprinkling water on the road in direct sunlight will make you feel stuffy. Why?
2. Why do vegetable farmers often cover vegetable fields with plastic film in cold winter?
(4) Experimental questions
A classmate wrote the following experimental report when he was doing the boiling experiment of water. Please read this experimental report carefully and answer the questions raised.
laboratory report
Experimental purpose: To observe the boiling of water.
Experimental steps:
① Put a proper amount of water in the beaker, put the beaker on the asbestos net, and then insert the thermometer into the water.
② Light the alcohol lamp and heat the beaker.
③ Observe and record.
(4) After the experiment, tidy up the equipment.
Observation record:
(1) When the water temperature is lower than 60℃, with the increase of water temperature, there are more and more bubbles at the bottom of the cup, and a few bubbles float up.
(2) When the water temperature is between 60℃ and 90℃, the bubbles at the bottom of the cup gradually decrease and rise.
③ When the temperature is between 90℃ and 100℃, the bubbles rise faster and faster.
④ When water boils, a large number of bubbles rise rapidly and the temperature is constant at 98℃.
⑤ Remove the alcohol lamp and stop boiling.
Experimental conclusion:
(1) boiling is a simultaneous vaporization phenomenon on the surface and inside of liquid.
② When water boils, the temperature remains unchanged.
answer the question
Do you think this experimental report is complete? If not, what items need to be added?
② Is the experimental conclusion comprehensive? If it is not comprehensive, please fill it in.
Test answer
(1) 1. Evaporation, vaporization, any 2. Evaporation endothermic, less than 3. Inhale and cool 4. Gas, evaporation, boiling.
5. Some, surface, interior, suction, constant, boiling point 6. Foam, get bigger, burst
7. suck; Constant; Different 8. Reduce; Minus 9. Suction; let go
10. Reduce the temperature, compress the volume, and compress the volume. 1 1. Water droplets, water vapor; Liquefaction.
12. Heat release from steam liquefaction. 13. The melting point is lower. 14. The boiling point of water is lower than that of oil.
15. Avoid the condensation of water vapor in the oral cavity on the mirror surface, so that the teeth can't see clearly.
(2) 1.b2.c3.d4.c5.b6.b7.c
8.D 9。 C 10。 A 1 1。 C 12。 D 13。 C
(3) 1. Water evaporates to absorb heat, which can lower the room temperature. However, the pavement temperature under direct sunlight is much higher than the air temperature, and the water sprinkled on the pavement evaporates to form water vapor with a temperature higher than the air temperature, which makes people feel sultry.
2. Prevent air flow on vegetable surface, reduce vegetable evaporation and soil moisture. In addition, heat should be released when water vapor liquefies into small water droplets at night, which can prevent vegetables from freezing.
(4) ① Incomplete, experimental equipment should be supplemented.
(2) Incomplete, add "When the temperature of water is lower than the boiling point, water will not boil".
Math: 1, India has the same splendid culture as China. In ancient India, there was an interesting math problem: a group of bees landed on peony and gardenia. The difference between the two is three times, flying to the Chinese rose. Finally, there is a little bee flying between the fragrant jasmine and magnolia, and there is a bee.
2. In a container with a concentration of 10? 90 ml of 5% physiological saline, container B contains 1 1? 7% saline is 2 10 ml. If the same amount of brine is poured out from container A and container B first, and then they are poured into another container and stirred evenly, the same concentration of brine is obtained, and ml brine is poured out from each container.
3. In the figure below, A is the point outside ⊙O with a radius of 3, the chord BC//AO and BC=3. Connect alternating current. Shadow area is equal to (∏ take 3. 14)
4. Use the number of 10 from 0 to 9 to form several prime numbers, each number is used exactly once, and the minimum sum of these prime numbers is.
5. Driving from Shanghai to Nanjing was originally planned to arrive at noon 1 1: 30, but the speed was accelerated after the start, and it reached 1 1 point. When I returned the next day, I set off from Nanjing at the same time, drove at the original speed of120km, then sped up again, and arrived in Shanghai at exactly 60.
6. Fill the numbers of 10 from 0 to 9 in the box below, and the equation will be established. Now "3" has been filled in, please fill in the other 9 numbers (note: the first number cannot be 0).
(□□□+□-□□)×3□÷□□=2005
7. Some soldiers lined up. They counted off from left to right for the first time, 1 to 4, and from right to left for the second time, 1 to 6. In both cases, exactly five soldiers reported 3, and the number of soldiers in this row was the largest.
8. Place two rectangles as shown in the figure, where m is the midpoint of AD, and the shaded area is =.
9. After the surface of a large cuboid is painted red, it is divided into several small cubes with the side length of 1, of which exactly two small cubes painted red are 2005, and the minimum volume of a large cuboid is.
1 5
2 6
1 6
5 1
4 6
4 2
10, as shown in the figure, six 3×2 small grid tables are combined into a 6×6 large grid table. Please fill in the numbers in 1 ~ 6 in the blank, so that the numbers in each row and column are different, and so are the numbers in the original six 3×2 small grid tables.
Second, short answer questions (***2 questions, each question 10)
1 1. Someone went to the flower shop to buy flowers. He only has 24 yuan. He planned to buy six roses and three lilies, but he didn't have enough money, so he had to buy four roses and five lilies, so that he had more money left in 2 yuan. Please calculate, which is more expensive, two roses or three lilies?
12. Try to put these 99 small squares with side length into a cube with side length of 1 without overlapping. If you can do it, draw a method. If not, please explain why.
The 5th "Walking into the Wonderful Mathematics Garden"
China Youth Mathematics Forum Fun Mathematical Problem-solving Skills Exhibition Competition-Preliminary Competition
Seventh grade examination paper (volume b)
Fill in the blanks (*** 14, full mark 150. 1 ~ 4 has 8 points for each question, 5 ~ 8 has 10 for each question, 9 ~ 12 has 12 for each question, and 65438+.
1. Found 9+49+299+8999+99999=.
2. Calculation:.
3. Natural numbers are written in decimal and hexadecimal, and this natural number is.
4.500 Jin cucumber, the original moisture accounted for 99%. A week later, water accounted for 98%. At this time, the cucumber weighs 100 kg.
5. Take some points in an equilateral triangle with a side length of 2cm. If the distance between two points must be less than 1cm, at least one point should be taken.
6. Equation (fill in A or B).
(a) There is an integer solution; (b) There is no integer solution.
7. A square piece of paper has 2007 points, plus four vertices ***20 1 1 points, and any three points are not * * * lines. A triangle with these vertices can be cut out with scissors.
8. Fill in a number in each small box on the right, so that each row and column has 1, 2, 3, 4, 5. Then, the number in the small square in the lower right corner (the square surrounded by thick lines) should be.
9. There are four villages (points) of A, B, C and D, and a school should be built, so as to minimize PA+PB+PC+PD. Draw a picture to show where P is.
10. Sequences 2, 2, 4, 4, 6, 6, 6, ... Yes.
One digit of 1 1 Yes. Where it represents the integer part of x.
12. If both m and n are positive integers, the minimum value of is.
13. Draw 12 points so that the distance between each point and at least three of the other 1 1 points is 1.
14. As shown in the following table, a 7×7 square table has 9 numbers and 4 letters, where J, Q and K all stand for 10, and A can stand for 1 or1. Move the numbers or letters in the original column so that the total number of numbers and letters is greater than 65438.
The 18th "Hope Cup" National Mathematics Invitational Tournament
First, multiple-choice questions (this big question * *10 small questions, 4 points for each small question, 40 points for food. Only one of the four options in each of the following questions is correct. Please write the English letters of the correct answers in brackets after each question.
1, the red ribbon is a symbol of international concern about AIDS prevention and treatment. Cut the red ribbon into small pieces with human glue, and tie the folded red ribbon tightly on the chest with a pin, as shown in figure 1. The pattern formed by overlapping red ribbons is ().
(a) Square (b) Rectangular (c) Diamond (d) Trapezoidal
2. Let a, b and c be nonzero real numbers, then the value of is ().
(A)3 species (B)4 species (C)5 species (D)6 species.
The side lengths of 3 and 3 are,, and are ()
(a) equilateral triangle (b) obtuse triangle (c) right triangle
acute triangle
4. The ancients recorded the order by heavenly stems and earthly branches, among which Tiangan had10; Underground branch12; Zi Chou Mao Yinchen applied for a memorial service at noon, and arranged Tiangan 10 and Dizhi 12 into the following two lines;
a，B，D，E，G，N，N，N，E，B，D，N，N，E，D ...
Mao Yinchen's third ugly son applied for Yin Mao ugly son at noon, and Tatsumi applied for ugly son at noon. ...
From left to right, the column 1 is Jiazi, the second column is Ugly B, and the third column is Bingyin ... That's how the calendar year in China is obtained. For example, 2007 is the year of dinghai in Gregorian calendar, so from now on, the year of Jiahai in Gregorian calendar is ().
(a) 20 19，(b) 203 1，(c) 2043，
(d) There is no corresponding year number.
5. Real numbers A, B, M and N satisfy A.
Then the relationship between m and n is ()
(A)M & gt； N(B)M = N(C)M & lt； N (D) cannot be determined.
6. Several squares and isosceles right triangles are spliced into the figure shown in Figure 2. If the side length of the largest square is 7cm, then the sum of the areas of squares A, B, C and D is ().
(A) (B) (C) (D)
7. It is known that the inequality group about has exactly three integer solutions, so the range of a is ().
(A)≤(B)≤(C)