Physics in the first half of the second semester of junior high school about vaporization and liquef

1.Observe the boiling of water: Before the water reaches the boiling point, as the temperature increases, the number of bubbles rising from the wall of the beaker gradually increases After the water boils, it is continuously heated, and the thermometer is observed to remain unchanged (filled up or unchanged).

Stop the heat and you will see the water in the cup stop boiling. Explain that the water dissipates heat during the boiling process.

2.Yes, because the boiling point of water is 100° and the boiling point of alcohol is 78°, 100 78, can boil.

3.The answer is not to name a few. The display temperature of the thermometer is not accurate2The purity of the water varies3Several students had different angles of observation. It can be seen from this that scientific research should be conducted in accordance with the principles of rigorous science.

1: Increase, Constant, Stop, Suck

2: It should not boil, the alcohol is very volatile, and it has been completely volatilized before it has been heated to its boiling point.

3: If the experiment is done in the same location, the data should be the same.

However, there will be errors in the reading of each student, and it is possible that the thermometer is connected to the wall of the test tube.

Therefore, to conduct scientific research, it is also necessary to have the common experimental skills of scientific research and their own experimental quality!

1.Increase unchanged stop sucking.

2.It will boil because the boiling point of alcohol is 78 degrees Celsius and the boiling point of water is 100 degrees Celsius (at standard air pressure) When the test tube is put into the water, the water is constantly heating and the test tube is also constantly absorbing heat, and when the temperature of the water exceeds 78 degrees Celsius, the alcohol inside the test tube boils. (When the alcohol in the test tube absorbs heat to the boiling point, the alcohol in the test tube will boil if the heat is continued to be absorbed).

3.There are many possibilities! But I think in the lab, the air pressure should be the same! So I think it's because the thermometer is inaccurate.

1) Become more unchanged and stop sucking.

2) It can be boiled, and the boiling point of alcohol is lower than that of water.

3) Thermometer error, water purity, observation method.

Increase; No change; Stop it; Decalescence; Yes, because the boiling point of alcohol is lower than the bottom of water; The thermometer has a deviation in the air pressure greater or less than one standard atmosphere;

Vaporization and liquefaction

1. The change of substance from liquid state to gaseous state is called vaporization; The change of a substance from a gaseous state to a liquid state is called liquefaction;

2. Vaporization and liquefaction are mutually reversible processes, vaporization requires endothermy, liquefaction requires exothermy;

3. Vaporization can be divided into boiling and evaporation;

1) Evaporation: a slow vaporization phenomenon that can occur at any temperature and only occurs on the surface of a liquid;

Note: The speed of evaporation is related to (a) the temperature of the liquidThe higher the temperature, the faster the evaporation (water sprinkled in the room in summer dries out faster than in winter; Dry clothes in the sun and dry quickly); (b) It is related to the size of the surface area of the liquid, the larger the surface area, the faster the evaporation (when the clothes are cool, the clothes should be opened to cool, and the water should be swept away in order to dry quickly when there is standing water in the ground); (c) It is related to the speed of air flow on the surface of the liquid, the faster the air flow, the faster the evaporation (cool clothes should be cooled in a ventilated place, and the fan should be turned on in summer to cool down);

1) Boiling: at a certain temperature (boiling point), the violent vaporization phenomenon that occurs simultaneously on the surface and inside the liquid;

Note: (a) Boiling point: The temperature at which the liquid boils is called the boiling point; (b) The boiling point of different liquids is generally different; (c) The boiling point of the liquid is related to the pressure, the higher the pressure (pressure cooker cooking) (d) The conditions for the liquid to boil: the temperature reaches the boiling point and continues to absorb heat;

2) The difference and connection between boiling and evaporation:

a) they are both vaporization phenomena and both absorb heat; (b) boiling occurs only at the boiling point; Evaporation can take place at any temperature; (c) boiling occurs simultaneously inside and outside the liquid; Evaporation takes place only on the surface of the liquid; (d) boiling is more intense than evaporation;

4) Evaporation can cause cold: sprinkle water in the room in summer to cool down; People sweat to cool down; When you have a fever, apply alcohol to ** to cool down;

5) Different objects evaporate differently: for example, alcohol evaporates faster than water;

4. Liquefaction methods: (1) reduce temperature; (2) Compression volume (increase pressure, increase boiling point) such as: hydrogen storage and transportation; Liquefied gas;

Vaporization: Evaporation: less water in the river, less water in the bottle, less alcohol, rubbing alcohol to cool down when you have a fever, wiping your forehead with a wet towel to cool down, shivering cold just after swimming, the dew is gone soon after the sun comes out, the grain is dried, wet clothes are dried in summer, hair is dried, the salt works use seawater to dry salt, the cold winter just enters the warm room from the outside, and the comrades who wear glasses know that there will be a layer of fog on the lenses, and it will be gone after a while, and the process of disappearance is evaporation.

Boiling: The water in the kettle is almost boiled dry, liquefaction: the cold winter has just entered the warm room from the outside, and comrades with glasses know that a layer of fog will appear on the lenses, the formation of fog, the formation of hot gas, the breath to the hands, the warming of the hands, the formation of clouds, the formation of dew,

Vaporization (evaporation): 1The river becomes less watery.

2.There is less water in the bottle.

3.If you have a fever, rub it with alcohol to cool down, and wipe your forehead with a wet towel to cool down.

4.Just after swimming, I just got ashore and shivered coldly.

5.Soon after the sun came out, the dew was gone, and the grain dried.

6.Wet clothes dry out in the summer.

7.Hair is blow-dry.

8.The salt works use seawater to dry salt.

Liquefaction: 1As soon as the cold winter enters the warm interior from outside, a layer of fog appears on the lenses.

2.Fog formation. I breathed into my hands, and my hands became moist and warm.

3.The formation of dew.

1. The change of substance from liquid state to gaseous state is called vaporization; The change of a substance from a gaseous state to a liquid state is called liquefaction;

2. Vaporization and liquefaction are mutually reversible processes, vaporization requires endothermy, liquefaction requires exothermy;

3. Vaporization can be divided into boiling and evaporation;

1) Evaporation: a slow vaporization phenomenon that can occur at any temperature and only occurs on the surface of a liquid;

Note: The speed of evaporation is related to (a) the temperature of the liquid: the higher the temperature, the faster the evaporation (the water sprinkled in the room in summer dries faster than in winter; Dry clothes in the sun and dry quickly); (b) It is related to the size of the surface area of the liquid, the larger the surface area, the faster the evaporation (when the clothes are cool, the clothes should be opened to cool, and the water should be swept away in order to dry quickly when there is standing water in the ground); (c) It is related to the speed of air flow on the surface of the liquid, the faster the air flow, the faster the evaporation (cool clothes should be cooled in a ventilated place, and the fan should be turned on in summer to cool down);

2) Boiling: at a certain temperature (boiling point), the phenomenon of violent vaporization that occurs simultaneously on the surface and inside of a liquid;

Note: (a) Boiling point: The temperature at which the liquid boils is called the boiling point; (b) The boiling point of different liquids is generally different; (c) The boiling point of the liquid is related to the pressure, the higher the pressure (pressure cooker cooking) (d) The conditions for the liquid to boil: the temperature reaches the boiling point and continues to absorb heat;

3) Difference and connection between boiling and evaporation:

a) they are both vaporization phenomena and both absorb heat; (b) boiling occurs only at the boiling point; Evaporation can take place at any temperature; (c) boiling occurs simultaneously inside and outside the liquid; Evaporation takes place only on the surface of the liquid; (d) boiling is more intense than evaporation;

4) Evaporation can cause cold: sprinkle water in the room in summer to cool down; People sweat to cool down; When you have a fever, apply alcohol to ** to cool down;

5) Different objects evaporate differently: for example, alcohol evaporates faster than water;

4. Liquefaction methods: (1) reduce temperature; (2) Compression volume (increase pressure, increase boiling point) such as: hydrogen storage and transportation; Liquefied gas;

1.The purpose of this experiment is to study the relationship between the speed of evaporation and the liquid (surface area), and when doing this experiment, it can be found that the alcohol in the bottle with a large diameter evaporates (fast) than the alcohol in the bottle with a small diameter (optionally "fast" or "slow"), this experiment shows that (the surface area of the liquid is large, the evaporation is faster; Conversely, if the liquid surface area is small, the evaporation is slower).

2.Xiao Shen finished swimming and came up from the pool to feel cold. Please imagine the general situation of Xiao Shen at that time, feel and analyze the reasons for "cold".

Answer; The water on the body is evaporated, and after coming up from the pool, because the body is full of water, because there is air flow, the water will be evaporated, and the vaporization will absorb heat, and the heat on the body will be sucked away, and it will naturally feel cold.

Please cite again. 2. Three similar examples from life.

For example; After taking a shower, especially in winter, you will feel cold before you wipe your body. (Vaporization and endothermy).

Vaporization, liquefaction, boiling.

1.When the water is boiled, the water vapor escapes from the spout mouth, the water vapor is invisible, the water vapor meets the cold air, it will condense into small water droplets, and the "white gas" that you usually see is these small water droplets, not the gaseous water vapor, and the glass can receive water droplets formed by small water droplets, which shows that (water is first heated and vaporized and then liquefied in cold).

2.In summer, there are many small water droplets on the outer wall of the box containing frozen drinks, which are made (liquefied and exothermic).

3.Take a piece of paper and fold it into a carton, fill the carton with an appropriate amount of water, and heat it with an alcohol lamp until the water boils, but the carton is intact, think about it, why is that? Answer; Because there's water in the paper, the temperature of the paper is going to be low, despite the fire.

Study physics well, and now you can't think that the hard things are ahead.

1 Surface Area Fast All other things being equal, the larger the surface area of the liquid, the faster it evaporates.

2 The evaporation of water in the body takes away a lot of heat, so it is cold Example Rub alcohol to cool down when you have a fever1 Water is first heated and vaporized and then liquefied when it is cold.

2. Water vapor liquefies when cold.

3. Water vaporization takes away a lot of heat and cannot reach the ignition point of the paper.

The surface area is fast and the temperature and air flow are the same, the larger the surface area of the liquid, the faster the evaporation.

Evaporation area Fast The speed of evaporation is related to the evaporation area of the liquid, the larger the area, the faster the evaporation, and vice versa.

1 Surface area fast All else being equal, the larger the surface area, the faster the evaporation.

2. Evaporation absorbs heat Extinguish the fire with water In summer, it is cool to wipe your face with a wet towel.

3. The temperature of glass is low and the boiling point of water vaporization is 100 degrees, while the ignition point of paper is greater than 100 degrees.

Vaporization: It is the process by which an object changes from a liquid state to a gaseous state.

Vaporization includes evaporation and boiling.

Evaporation is the vaporization of the surface of a liquid at any temperature.

The speed of evaporation is related to the temperature, the size of the liquid surface area, and the speed of air flow on the liquid surface.

Boiling is the phenomenon of simultaneous vaporization of the surface and interior of a liquid at a certain temperature.

The temperature at which a liquid boils is called the boiling point. Different liquids have different boiling points.

The boiling point of a liquid is related to the air pressure on the surface of the liquid. The higher the air pressure, the higher the boiling point.

Liquefaction: The process by which the gaseous state of an object becomes liquid.

Coagulation: Water freezes - [liquid exothermic becomes solid].

Melting: Ice turns into water - [Solid absorbs heat and becomes liquid].

Vaporization: Dry wet clothesThe water sprinkled on the ground in the hot summer quickly dried up. [Liquid absorbs heat and becomes gas] Condensation: 1 Formation of ice flowers2 Formation of frost 3 Iodine vapor becomes iodine5 Formation of snow [Gas exothermic directly becomes solid].

Sublimation: Mothballs become smaller. 【Solid exothermic directly into gas】Liquefaction:

1 Water vapor becomes water, 2 Natural gas is compressed into liquefied gas, 3 Gas in a lighter, liquid is compressed, 4 The refrigerator is opened, and the white gas is water vapor liquefied, 5 Oxygen becomes liquid oxygen [gas exothermic becomes liquid].

This question is taught by the teacher to almost every class of students, and it is a typical example problem.

The cauldron can absorb heat all the way from the flame, but the water in the pot is up to 100 degrees, and the bowl is in contact with the water at 100 degrees, and the water in the bowl does not boil, and he cannot absorb heat all the time.

d, the boiling conditions are:1The temperature reaches boiling point 2Continue to absorb heat.

Although the water in the bowl can reach the boiling point, it cannot continue to absorb heat (the heat absorbed by the pot is used to vaporize the water in the pot), so it cannot be.

Because the soup is to boil to meet 1Boiling point 2Continue to heat, but when the water in the pot boils, the temperature will not change, so choose D