"Exploring the Characteristics of Melting and Solidification" Material Forms and Their Changes PPT Courseware

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"Exploring the Characteristics of Melting and Solidification" Material Forms and Their Changes PPT Courseware

teaching objectives

1. Know what melting and solidification are, and understand the heat absorption of melting and the heat release of solidification.

2. Know the melting and solidification characteristics of crystals and amorphous crystals. Understand the physical meaning of melting curves. If you know what the melting point and freezing point are, you can look up the melting point table.

3. Be able to use the knowledge of melting and solidification to explain relevant phenomena in nature and life.

4. Experience the entire process of exploring the melting and solidification characteristics of crystals and amorphous crystals, and be able to use image methods to intuitively represent the temperature changes with time when solids melt.

5. Cultivate students’ scientific attitude of patiently and meticulously observing phenomena, collecting data realistically, and carefully analyzing and summarizing rules.

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.

Discussion in each group

What conditions are required for substances to melt and solidify?

Are the laws of melting and solidification of different substances the same?

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.

3. Melting point and freezing point

Solids are divided into crystalline and amorphous. Crystals have a certain melting temperature, amorphous ones do not.

Melting point: The temperature at which a crystal melts.

Freezing point: The temperature at which a crystal solidifies.

Classification of solids

crystal

A solid with a fixed melting point.

Conditions for crystal melting: endotherm, reaching melting point

Common crystals: sea wave, ice, salt, naphthalene, quartz, various metals, etc.

Amorphous

A solid with no fixed melting point.

Conditions for amorphous melting: endotherm

Common amorphous materials: beeswax, rosin, asphalt, glass, etc.

Use your brain

1. A classmate used a substance to do a melting experiment. When the temperature of the substance reached 75, the temperature was recorded every 1 minute and the following data were obtained: 75°C, 77°C, 79°C, 80.5°C, 80.5°C, 80.5°C, 80.5°C , 82℃, 84℃, it can be known that the substance is ( ). (Fill in "crystalline" or "amorphous")

2. Among the following natural phenomena, what is formed through melting is ( )

A. The ice and snow in the river turn into water in spring B. The dew on the flowers and leaves in the summer morning

C. Fog covering the earth in autumn D. Snowflakes flying in the sky in winter

3. Slowly heat the ice-water mixture. Before the ice melts, the temperature of the water is ( ) 0°C.

(Fill in "greater than", "less than" or "equal to")

4. As shown in the figure, it is the ( ) image of the sea wave. The AB segment indicates that the sea wave is in the ( ) state and is in the ( ) process. The BC section is in the ( ) process. During this process, the sea wave ( ) has heat and temperature ( ). The CD section sea wave is in the ( ) state. The state of sea waves at 48°C is ( ).

practice

1. Which of the following statements about melting and solidification is incorrect ( )

A. Various crystals have certain melting points

B. The temperature remains unchanged when the crystal melts, indicating that the crystal does not need to absorb heat when melting.

C. Only the crystal melts and the solidification temperature remains unchanged

D. All kinds of liquids release heat when they solidify.

2. In the northern winter, car drivers often use a mixture of water and alcohol as a cooling agent in the car cooling system. This is because this liquid has ( )

A.Higher boiling point B.Lower freezing point

C. Good heat absorption D. Good combustion property

think about it

1. When a classmate was doing the "sea wave melting" experiment, he used a thermometer to measure the temperature of the sea wave during the heating process. The main steps were:

A. Fully contact the glass bulb of the thermometer with the sea waves, and do not touch the bottom or wall of the container.

B. Understand the temperature at which sea waves melt and choose a thermometer with a suitable range.

C. Read the temperature. When reading, the glass bulb of the thermometer is still in contact with the sea waves.

D. Observe the range and graduation value of the thermometer

The reasonable order of the above steps is ＿＿＿＿＿

In the winter when the temperature is -20°C, the upper surface temperature of the ice on the river is _______°C, and the lower surface temperature of the ice is _______°C.

Put the ice-water mixture into a room at -2°C and it will:

A. Continue to melt B. Continue to solidify

C. Neither melts nor solidifies D. Unable to judge

As shown in the picture, insert the test tube containing crushed ice cubes into the crushed ice cubes in the beaker, and then slowly heat the bottom of the beaker. When the ice cubes in the beaker are half melted, the ice cubes in the test tube will ()

A. All melted B. Does not melt

C. Melt half of D. start to melt

The melting point of sea wave is 48, then the sea wave of 48 is:

A. It must be solid.

B. It must be in liquid state.

C. It must be a solid-liquid coexistence state.

D. All three of the above are possible

As shown in Figure 4-6, the beaker is filled with ice-water mixture and the test tube is filled with ice at -5°C. They do not exchange heat with the outside world. Will the ice in the test tube heat up to 0°C? Will the ice in melt?

Basic rules:

(1) The conditions for crystal melting: one is _______________, and the other is _______________.

(2) The melting point and freezing point of the same substance are ________, and the melting points of different substances are ________.

(3) Melting______, solidification______.

basic skills:

(1) Skills in using alcohol lamps and thermometers;

(2) Skills in assembling vertically combined experimental equipment.

Basic method: method of using experimental data to draw images to analyze problems

Operation:

Classwork: Questions 1, 2, 3, and 4 on page p99.

Tutorial (preview): a. What are sublimation and sublimation? Give three examples of sublimation and sublimation in life. b. Know that sublimation needs to absorb heat and sublimation needs to release heat. c. Give some examples of applications in daily life where sublimation needs to absorb heat and sublimation needs to release heat.

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"Exploring the Characteristics of Melting and Solidification" Material Forms and Their Changes PPT Courseware 2:

"Exploring the Characteristics of Melting and Solidification" Material Form and Its Changes PPT Courseware 2 Learning Objectives 1. Know what melting and solidification are. Understand the endotherms of melting and the exotherms of solidification. Know the characteristics of crystalline and amorphous melting and solidification. Understand the physical meaning of melting curves. 2. know..

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Update Time: 2024-10-18

This template belongs to Physics courseware Guangdong and Shanghai version of eighth grade physics volume one industry PPT template

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