"Melting and Solidification" Changes in State of Matter PPT Courseware 11

"Melting and Solidification" Changes in State of Matter PPT Courseware 11

1. There are three states of matter: solid, liquid, and gas.

2. The change of matter from one state to another is called change of state of matter

1. Melting and Solidification

Melting – The process of a substance changing from a solid state to a liquid state is called melting.

Solidification - The process of a substance changing from a liquid to a solid state is called solidification.

2. Explore the temperature changes during solid melting

Ask a question: Do the temperature changes of different substances during the melting process from solid to liquid are the same?

Conjecture hypothesis: The melting process must be heated, so the material must absorb heat. The temperature may also be rising at this time.

(1) Experimental device:

(2) Advantages of the water bath method: it can extend the time for solid melting and facilitate observation and recording of temperature.

(3) Hypo and paraffin melting data table

Crystal melting characteristics:

Heat continues to be absorbed and the temperature remains constant.

Understand the crystal melting curve:

(1) The material in segment AB is in a solid state, indicating the process of crystal endothermic heating.

(2) The material in the BC segment is in a solid-liquid coexistence state, indicating the crystal melting process, absorbing heat, and the temperature remains unchanged (that is, it will melt only at the melting point).

(3) The material in segment CD is in a liquid state, which means that the liquid absorbs heat and heats up.

(4) Point B means that the material has reached the melting temperature, but has not started to melt, and the material is completely in a solid state; point C means that the crystal has just completely melted, and the material is in a liquid state.

(4) Melting curve analysis of sea wave and wax:

1. Solids are divided into: crystalline and amorphous

Crystal: sea wave, ice, salt, naphthalene, various metals

Amorphous: wax, rosin, glass, asphalt

2. Crystals have melting points, while amorphous crystals have no melting points.

3. Two conditions for crystal melting: reaching the melting point and continuing to absorb heat

4. After an object absorbs heat, its temperature does not necessarily rise.

The reason is: when the crystal melts, it absorbs heat and the temperature remains unchanged.

solidification process of crystals

1. The crystal only starts to solidify when it reaches a certain temperature (freezing point);

2. The temperature of the crystal does not change during the solidification process (freezing point);

3. During the solidification process, solid and liquid coexist;

4. The solidification process releases heat.

Melting points of several crystalline substances

1. Why is tungsten used as the filament of incandescent lamps?

2. The lowest temperature in my country reaches -50 ℃. Can I use a mercury thermometer to measure the temperature? What thermometer should be used? 3. What is the freezing point of water?

Students read the melting points of several common substances in the textbook and answer the following questions:

1. Are all metals crystals?

2. Why is tungsten used as the filament of incandescent lamps?

3. Can I use a mercury thermometer to measure the temperature in the Arctic winter?

4. What is the freezing point of water?

4. Solidification

1. There is a definite temperature when the crystal solidifies;

There is no definite temperature at which amorphous solidification occurs.

2. Freezing point: The temperature at which a liquid crystalline substance solidifies.

For the same crystalline substance, freezing point = melting point.

3. Crystal solidification conditions:

(1) Reach the freezing point;

(2) Continue to release heat.

4. During the solidification process, the crystal releases heat and the temperature remains unchanged.

Classroom exercises

1. Why in the northern winter, just putting a few buckets of water in the vegetable cellar can prevent the temperature inside the vegetable cellar from being too low and prevent the vegetables from freezing?

2. If you take the melting ice into a room with a temperature of 0℃, will the ice continue to melt?

3. In summer, use 0℃ ice or 0℃ water of equal mass to cool soda. The result is ( )

A. The effect of using ice is better because the temperature of ice is low

B． Using water works well because water absorbs heat more easily than ice

C. The effect of using ice is good because the temperature of ice's heat absorption does not change.

D． Both have the same effect

4. What kind of physical state change does the following phenomenon belong to?

(1) In spring, when the ice and snow melt, it is ______.

(2) Pouring molten iron into a mold to cast iron parts is ______.

5. Xiao Ming is doing an experiment on the melting of a certain substance. When the temperature of the substance reaches 36°C, the temperature is recorded every 1 minute and the following set of recorded data is obtained: 36°C, 39°C, 42°C, 45°C, 48°C, 48℃, 48℃, 51℃, 54℃, 57℃. This substance is a ______ body and its freezing point is ______.

1. Melting means: solidification means:

2. Melting point refers to:

3. Conditions for crystal melting:

4. Conditions for crystal solidification:

5. The difference between crystal and amorphous

6. The melting point and freezing point of the same crystal are ____ (same, different)

7. Is the statement "The temperature of an object absorbing heat must increase" correct?

8. What are the common crystals? What are the common amorphous crystals?

9. Some people say, "If it snows and it doesn't get cold, it becomes cold." Is this statement true?

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