Here's why:
* Solubility: The rate at which a substance dissolves (like sugar in water) is generally higher in warm water. While this might seem like it would help crystals grow faster, it actually hinders their formation.
* Nucleation: Crystals form when dissolved molecules come together and start arranging themselves in a specific, repeating pattern. This process, called nucleation, is more likely to occur in cooler water. Warm water can make it harder for these molecules to slow down and arrange themselves.
* Evaporation: Crystals grow as the solvent (water) evaporates, leaving behind the dissolved molecules to form the crystal structure. Warmer water evaporates faster, which can sometimes lead to faster crystal growth, but it also increases the risk of the solution becoming supersaturated, making it more likely to form many small crystals rather than a few large ones.
To summarize:
* Warm water increases the rate of dissolving. This means more molecules are in solution, but it also makes it harder for them to come together and form a crystal.
* Cool water is more likely to promote nucleation, leading to the formation of more crystals.
* Warm water can lead to faster evaporation, but also increases the risk of supersaturation, which can result in smaller crystals.
Therefore, for growing larger, well-defined crystals, it's usually better to use cooler water.
Exceptions:
There are some exceptions, like growing crystals from certain chemicals that are more soluble in warm water. However, in general, cooler temperatures are better for growing large, well-formed crystals.
