"Melting and Solidification" Changes in State of Matter PPT Courseware 6

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"Melting and Solidification" Changes in State of Matter PPT Courseware 6

1. Changes in physical state

The process by which we change a substance from solid to liquid is called melting.

Like ice turning into water.

The process of changing from liquid to solid is called solidification.

Like water turning into ice.

Substances can change from liquid to solid or from solid to liquid.

The state in which matter exists is related to temperature.

Use the above conclusions to analyze the volcanic eruption phenomenon:

Rocks can become liquid at high temperatures and become solid when the temperature is lowered.

Experiment: The law of temperature change when solid melts

observe:

1. When sodium thiosulfate and rosin are heated, the reading of the thermometer changes.

2. Their states at different temperatures.

3. Their state and temperature when melting

Record: Data from the experiment.

Thinking: Do sodium thiosulfate and rosin have the same temperature changes when they melt?

Observe phenomena

From observations of sodium thiosulfate melting:

a: Before the temperature rises to 48°C, sodium thiosulfate is solid.

b: Sodium thiosulfate melts from the beginning until it is completely melted. Although it absorbs heat, the temperature remains unchanged at 48°C.

c: After all the sodium thiosulfate melts into a liquid state, it continues to absorb heat, and the temperature continues to rise from 48°C.

Analysis of experimental data on rosin melting (compared to sodium thiosulfate)

The melting of sodium thiosulfate is carried out at a certain temperature. If it does not reach this temperature, the sodium thiosulfate will not melt, the melting will not end, and the temperature will not rise. However, the melting of rosin is not carried out at a certain temperature. It does not melt at a certain temperature. It is a process of gradually softening and then thinning. During the entire process of melting, the temperature gradually rises. There is no specific temperature before melting begins.

What are the similarities and differences between the melting of sodium thiosulfate and rosin?

a The melting of sodium thiosulfate is carried out at a certain temperature, while the melting of rosin is not carried out at a certain temperature. It is a gradual softening process, and the temperature gradually increases during the melting process.

b There are horizontal segments in the melting image of sodium thiosulfate, but there are no horizontal segments in the melting image of rosin.

c Both sodium thiosulfate and rosin must absorb heat from the outside during the melting process.

crystal solidification laws

1. The temperature of the crystal does not change during the solidification process. This temperature is called the freezing point;

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

3. The crystal only begins to solidify when it reaches a certain temperature;

4. The solidification process releases heat.

Melting Characteristics of Crystalline and Amorphous Crystals:

A. Both crystals and amorphous materials absorb heat from the outside when melting, but the temperature remains unchanged when the crystal melts, and the temperature continues to increase when the amorphous melts.

B. Crystals melt at a certain temperature. The temperature at which crystals melt is called the melting point. Amorphous crystals do not have a certain melting temperature (amorphous crystals have no melting point).

C. Crystals are in a state of solid and liquid coexistence from the beginning of melting to complete melting. There is no state of solid and liquid coexistence when amorphous crystals melt.

think

Read the table of melting points of several crystals and think:

1. Are all the substances in the table crystals?

2. Do different crystals have the same melting point?

3． Why is tungsten used as the filament of electric lamps?

4. Why do northern my country use alcohol thermometers instead of mercury thermometers? (The melting point of alcohol is higher than the melting point of mercury)

2. Solidification of matter

1. Solidification is the reverse process of melting.

2. Substances must release heat when they solidify.

3. The temperature remains unchanged during the solidification process of the crystal. This temperature is called the freezing point of the crystal. The freezing point of the same crystal is the same as the melting point. Amorphous crystals have no freezing point.

think

1. People often say that "if it snows, it becomes cold when it doesn't get cold." Does this statement make sense?

2. The lowest temperature in northern Heilongjiang Province of my country has dropped to minus 52.3 degrees Celsius. Can I still use a mercury thermometer at this time? What kind of liquid thermometer should I use?

practise

1. The basis for dividing solids into crystalline and amorphous is ________.

2. Judgment: Various solids have certain melting points ( )

3. During the science review class, the teacher wrote a couplet. The first couplet is "Ice water in the cup, the temperature of the water does not drop when it freezes"; the second couplet is "There is ice in the dish, but the temperature of the ice does not rise". The material changes contained in the couplet are ______, and the reflection of a commonality is ______.

4. To heat the ice-water mixture, then ( )

A. The temperature of ice increases, but the temperature of water remains unchanged.

B. The temperature of the ice remains unchanged and the temperature of the water increases.

C. The temperature of the ice water increases together

D. When ice melts into water, the temperatures of both ice and water remain unchanged.

5. The group of the following substances that all belong to crystals is ( ):

A.Iron, salt, rosin

B. Aluminum, paraffin, glass

C. Ice, asphalt, rosin

D.Naphthalene, crystal, salt

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For more information about the "Melting and Solidification Changes in State of Matter" PPT courseware, please click the Melting and Solidification ppt Changes in State of Matter ppt tag.

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Update Time: 2024-11-24

This template belongs to Physics courseware People's Education Edition Physics for Grade 8, Volume 1 industry PPT template

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