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Name: Bob
Status: student
Grade: 6-8
Location: CA
Country: USA
Question:
How is it that crystals grow in cold temperatures?


Replies:
This is not "always" true, but usually is. Here is why. Most substances -- I am thinking here about substances dissolved in a solvent, usually water, are less soluble than at higher temperatures. So as the temperature is carefully and slowly decreased, the substance becomes less soluble and it forms a crystal (or crystals).

A few substances have reverse solubility in water. Those substances grow crystals by carefully and slowly increasing the temperature. There is another less common method of growing crystals, and that is by precipitating the crystal from the liquid phase of the substance with no solvent. In this case, crystals ALWAYS form by cooling the liquid, not heating it. The "reason" for this is that it always takes heat to melt a crystal. This fact guarantees that cooling the liquid produces crystals, not heating the liquid.

Vince Calder


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