Unformatted text preview: lastics How does a solid become a How does a solid become a liquid?
1. Start with very cold ice and gradually heat it. If you could see the molecules, you would see each molecule shaking faster and faster, but still held in one position by the other molecules around it. Keep heating your ice
Keep heating your ice When the temperature reaches 0° C, the molecules begin to break free.
The molecules begin to move freely around each other.
The molecules enter the liquid state. Melting point = the temperature at which a substance changes from a solid to a liquid. 60° 20° e u a ep m T
e 0° 20° 0 Heat (kilojoules) 60° 20° e u a ep m T
e 0° 20° 0 Heat (kilojoules) The amount of heat required to melt 1 kg of a solid is called its heat of fusion
measured in kilojoules per kilogram
k J / k g heat of fusion e u a ep m T
e 0° Heat (kilojoules) Water’s heat of fusion is 334 kJ/kg That is the same amount of energy you would spend if you climbed all the stairs in a 110story tall building.
No, not a 110foot tall building . . . a 110story building! Freezing
Freezing As you know, if you can melt something, you can cool the liquid again to freeze it.
When you cool a liquid, the particles begin to slow down.
The attractive forces between the particles begin to catch the particles, and crystals begin to form. Freezing point = – the temperature at which attractive forces trap particles in a cooling liquid and form crystals. Think: If the melting point of iron is 1,535° C, at what temperature does iron freeze? Noncrystalline solids
Noncrystalline solids Noncrystalline solids, like glass, butter or wax, do not have a definite freezing or melting point.
• If you slowly heat cold butter, it gradually gets softer and softer until it is completely liquid....
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- Winter '08