"Melting and Solidification" Temperature and Physical State Changes PPT Courseware 3

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"Melting and Solidification" Temperature and Physical State Changes PPT Courseware 3

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melting and solidification

Melting The process by which a substance changes from ______ to ______

Solidification The process by which a substance changes from ______ to ______

Crystalline and amorphous

Solid classification

Crystals have a fixed ______ temperature

Amorphous has no fixed ______ temperature

melting point and freezing point

Melting point The temperature at which a crystal ______

Freezing point The temperature at which a crystal ______

Characteristics (1) The same crystal has the same freezing point and ______, while amorphous crystals have no melting point and ______;

(2) ______ must be done during the melting process and ______ must be done during the solidification process.

Melting and solidifying images

The melting and solidification process of substances is accompanied by changes in two physical processes: endothermic and exothermic, and temperature changes. Images can intuitively express their changing processes. As shown in Figure A, it is the temperature change curve when the crystal melts. Section AB is a solid state, and the endothermic temperature increases; Section BC represents the melting process, which continues to absorb heat, but the temperature remains unchanged; Section CD represents that everything melts into a liquid state. , the endothermic temperature continues to rise. Figure B shows the temperature change curve when amorphous melts. During the heating process, the solid material first softens, then gradually becomes thinner, and finally becomes liquid. The temperature continues to rise throughout the process and there is no certain melting temperature.

Figure C is the temperature change graph when the crystal solidifies. The EF segment is in a liquid state, and the exothermic temperature decreases; the FG segment represents the solidification process, where solid and liquid coexist, and the exothermic temperature remains unchanged; the GH segment is in a solid state, and the exothermic temperature decreases. As shown in Figure D, it is the temperature change graph when the amorphous solidifies. As the temperature decreases, it gradually becomes thicker, viscous, and hard, and finally becomes a solid.

[Example] In the experiment of exploring the "melting characteristics of ice",

(1) As shown in Figure A, it is an image of the temperature change with time when ice is heated, which Xiao Ming made based on experimental data. From the analysis of the image, it can be seen that the melting point of ice is _________℃, and the characteristics of its melting process are __________________. The substance is in _________ within the 6th minute (select "solid state", "liquid state" or "solid-liquid coexistence state").

(2) In order to make the material heat faster, another team used the experimental device as shown in Figure B. You think the shortcoming of this device is ____________________.

Analysis: (1) It can be seen from Figure A in the question that the temperature of this substance remains unchanged at 0 °C during the melting process, so its melting point is 0 °C. Within the 6th minute, the substance is in the process of melting, so it is in a solid-liquid coexistence state. (2) As shown in the question, substance B is placed in a test tube. The substance above is too far away from the heat source and is heated unevenly.

Answer: (1)0 Absorb heat and the temperature remains unchanged. Solid-liquid coexistence state. (2) The substance is heated unevenly.

Knowledge point 1: Melting and solidification phenomena

1. Among the following natural phenomena, the one that belongs to melting phenomenon is ()

A. In winter, the lake freezes

B. In summer, the water sprinkled on the ground dries up

C. In autumn, water vapor in the air turns into fog

D. In spring, the ice in the river melts into water

2. In an environment of 0 ℃, if a piece of ice at 0 ℃ is put into water at 0 ℃, what will happen is ()

A. All the ice melts

B. A small part of the ice melts

C. A small part of the water solidifies

D. The original masses of ice and water remain unchanged.

3. After the candle is lit, "wax water" appears around the candle wick. When there is wind, the "wax water" flows to the side and drips and turns into hard wax. As shown in the figure, during the above process, what happens The state of matter changes first to _____, then to _____.

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Update Time: 2024-11-25

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