Why do liquids solidify and make ice?

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Malibongwe Nqanqase

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Why do liquids solidify and make ice?
« on: 07/02/2009 10:30:01 »
Malibongwe Nqanqase  asked the Naked Scientists:
   
Hi Chris,

Why do liquids solidify to make, for instance in the case of water, ice?

Malibongwe Nqanqase

What do you think?

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Offline Chemistry4me

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Why do liquids solidify and make ice?
« Reply #1 on: 07/02/2009 10:40:20 »
Liquids are less ordered than solids, though in water some order remains just above the melting point. There is some free space to move (mean free path = 2 x 10 -10 m) but most of the molecules are touching. Ice, like all crystalline solids, has a high degree of order. The water molecules are held in fixed positions in a regular pattern. The molecules can vibrate, but they cannot move about. All true solids are crystalline.

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Offline Chemistry4me

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Why do liquids solidify and make ice?
« Reply #2 on: 07/02/2009 10:44:42 »
In terms of the kenetic theory, the particles in a crystal are seen as able to vibrate about their positions but, in general, unable to move away from them. However, in liquids, there is always a chance that some particles in/on the surface will have sufficient energy to escape-and to exert a vapour pressure.