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

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

learning target

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 what the melting point and freezing point are, and you will know the melting point table.

3. Be able to use the knowledge of melting and solidification to analyze related simple thermal phenomena.

Core test point: images related to the melting and solidification processes.

Preview before class

1. The process of a substance changing from a solid state to a liquid state is called ______, and the process of changing a substance from _______ to ______ is called solidification.

2. Although some solids continue to absorb heat during the melting process, the temperature remains ______. This type of solid is called ________, such as ______, _______, _______, etc.

3. During the melting process of some solids, as long as they continue to absorb heat, the temperature will continue to _______. This type of solid is called _______, such as _____, _______, ________, etc.

4. _______________________ is called the melting point and _______________ is called the freezing point; the melting point and freezing point of the same crystal are _________.

5. Which of the following statements is correct: ( )

A. Generally, the temperature of a substance remains constant during the melting and solidification processes.

B． After an object absorbs heat, its temperature must rise

C. The melting point and freezing point of the same substance are the same

D． Ice at 0℃ is cooler than water at 0℃

Lectures in class

Knowledge point 1. Melting and solidification

The process of a substance changing from solid to liquid is called melting. Melting is an endothermic process.

The process of a substance changing from liquid to solid is called solidification. Solidification is an exothermic process.

For example: when ice turns into water, it melts and needs to absorb heat; when water turns into ice, it solidifies and needs to release heat. In addition, wax, rosin, asphalt, glass, iron and other substances can also melt and solidify.

[Example 1] In the process of casting a bronze statue with a copper block, the physical change that occurs is ( )

A. A solidification process B. a melting process

C. Melt first and then solidify D. First solidify and then melt

[Exercise 1] (2014•Taian) When eating ice cream just taken out of the freezer, your tongue will often be frozen on the ice cream. This happens because of the water on the tongue ( )

A. melt b. Solidification c. Evaporate D. Sublime

Knowledge point 2. Crystal and amorphous

Solids are divided into crystals and amorphous according to their different melting characteristics. Crystals have certain melting points and freezing points, while amorphous do not.

The temperature at which a crystal melts is called the melting point. The temperature at which a crystal solidifies is called the freezing point.

Common crystals include: hyaline, quartz, crystal, ice, salt, alum, naphthalene and all metals.

Common amorphous materials include: glass, rosin, paraffin, asphalt, etc.

Note: (1) The main difference between crystals and amorphous is the presence or absence of melting point and freezing point. Crystals have a certain melting point and freezing point, while amorphous does not have a certain melting point and freezing point.

(2) The melting points of different crystals are generally different, and the melting point and freezing point of the same crystal are the same. The melting point of a crystal is a characteristic of the crystal itself. You can judge what kind of substance it is based on the melting point of the crystal.

(3) There must be two conditions for crystal melting: ① The crystal must reach the melting point ② It needs to absorb heat

There are two conditions necessary for crystal solidification: ① the crystal must reach the freezing point ② heat needs to be released

So when an object absorbs heat, the temperature does not necessarily increase, and when an object releases heat, the temperature does not necessarily decrease.

(4) Whether it is crystal or amorphous, it absorbs heat during the melting process and releases heat during the solidification process. However, during the melting and solidification processes of crystals, the temperature does not change when absorbing or releasing heat. The crystal continuously absorbs heat and heats up when melting, and continuously releases heat and cools down when solidifying.

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

"Exploring the Characteristics of Melting and Solidification" Material Forms and 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. ..

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Update Time: 2024-11-20

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

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