Why is a supersaturated solution necessary for crystallization to occur?
456274
Precipitation, or crystallization, only occurs when the solution is already holding more solute than it can regularly hold. As a result, the hypercollisons of the molecules cause bonding between them to occur and for the solute to precipitate.
867949
Because settling only works if there is no chemical reation involved. All of the prticals of some substances will not settle out of water. like sugar. Even if they do the time frame needed to accomplish this is to long.
900560
Most solutes (sugar in this case) have limited solubility (ability to dissolve) in most solvents (water in this case). This solubility varies with temperature - the hotter the solution, the higher the solubility. As mentioned in an earlier answer, this means more energy must be added to dissolve more solute. On the other hand, if energy is taken out of a solution, the solute will usually  come out of the solution, depending on the concentration.\n\nThis physical law that governs this is the 2nd law of thermodyamics.
711134
No. Most sugars can be crystallized.
799604
If the ionic compound is soluble, no precipitate is formed.\n\nOn the other-hand, if an ionic compound is not very soluble in the solvent, then it will precipitate out of solution.\n\nFor example, Sodium chloride is soluble and Silver nitrate is soluble, but if these solutions are mixed, some of the Silver ions will react with chloride ions and form solid Silver chloride precipitate.
784863
The precipitate is a solid, and it usually is in the form of a salt (i.e. NaCl)  If you are given an equation that begins with two liquids, for example, and one of the end products is solid (s), then you know that that is a precipitate.  \n\nPrecipitation can occur for a few different reasons.  One reason can be due to the insolubily of one of the reactants and wil result in precipitation  This can also be due to supersaturation of the mixture that causes the insoluble material to precipitate out of solution.\n\nWikipedia has a nice example using Silver Chloride (AgCl).
703543
Mmmm... Salt....\n\nYou will get a super-saturated solution. Like the sugar they use to make rock candy, salt dissolves better in hot water. Saturated means it has as much solute (salt, in your question) in it as will possibly dissolve, so a saturated solution at 60 degrees celsius has quite a lot of salt in it!\n\nAs the saturated solution goes back to normal temperatures, it eventually reaches the point where there is MORE salt in solution than would normally dissolve. This is called a super-saturated solution. It still looks like it did before, except saltier than normally possible.\n\nSeveral things can happen to a super-saturated solution as it cools. Either it appears unchanged, or crystals start to grow like when you are making rock candy. You would see crystals around the edges and on the sides and bottom of the container. Some substances like sodium nitrate are so soluable that they can crystalize all at once when disturbed, which looks like the solution instantly froze solid. Table salt does not normally do this, so just write that it would go from saturated to super-saturated and crystals would form.
8528
All freezing (or rather: crystallisation) occurs on surfaces or crystal seeds. Water freezes "from the bottom" because liquid water closer to freezing has a greater density than solid water (aka ice), so the frozen crystals float up. In cases where the solid has  a greater density than the liquid (probably the majority of cases), the solid will sink down.
68297
well without it their cells would shrivel up and die...\n\nwater is essential to dissolve most minerals and compounds in because it is a polar molecule and things are easily dissolved in it. the body takes advantage of these properties of water and our living system is based off of the properties of water and most of our bodies are actually made up of water.
950381
It takes energy not only to break up the solid solute into its individual particles, but also to force the solvent molecules apart.  Now, if the solute can offer the solvent some very attractive forces (like sodium ions and chloride ions do from table salt) the whole process will work. The energy required to break up chalk is just too great.
945741
Due to the fact that this salt is found as a hydrated salt (first Na2SO4.10H20 and then as Na2SO4.7H2O, so, with the increase of temperature it looses moisture (water)). When the Na2SO4.10H2O is heated the solution of this compound decreases because a solid phase and a liquid phase are formed after the initial heating.
680279
Technically a process can require the addition or extraction/removal of heat ENERGY.\n\nI cannot off the top of my head recognize a chem formula any longer, but adding oxygen to any system is oxidation and generates its own heat.  Tehcnically even iron rusting generates heat, just a very small amount, since any metal "rusting" is just it oxidizing.  \n\nAs far as the ice cubes, simply the removal of heat will not cause water molecule to become ice crystals,  I apologize, but I forget why.  I remember an experiment I saw and tried.  In a very clean container, pour distilled water. Now cover that container with another container that does not touch the first.  (Like putting a big bowl over a smaller bowl with the distilled water.  The water stays liquid all the way down to around -20 C.  But if you damage the stablility of the bowl by say gently tapping the side, the water will then turn to a solid.\n\nSnow in clouds form when the water molucle has a dust mote or other item to cling to and begin forming the ice crystal which eventually gets heavy enough to possibly fall all the way to the ground.
883409
I will assume that "salt" is referring to sodium chloride, NaCl.  The solubility of NaCl increases with increasing temperature and decreases with decreasing temperature.\n\nSince you are starting with a saturated solution (meaning that it contains the MAXIMUM amount of NaCl at that temperature) and you are cooling the solution to 20oC from 60oC, the cooler solution will not be able to keep the NaCl dissolved and you will observe small crystals of NaCl precipitating from the solution.
736055
when the solvent (liquid) can no longer dissolve any more solute (solid) and particles of the solute remain in the solution.\n\neg: sugar in tea...if you add too much sugar (solute) to the tea (solvent) the sugar sinks to the bottom and wont dissolve. \n\nTasty but saturated!
30770
Excellent question.  Food for thought for both of us.  Let's see- changing the pH of water could allow for greater or less solubility of minerals.  With more minerals in solution, the rate of evaporation increases while the boiling/freezing point lowers, as intermolecular attraction is decreased.  The opposite would then be true with less minerals in solution.
592262
sodium chloride definately or cesium fluoride (not sure)-evaporation of water solution\n\npresume you mean cubic close packing
872765
It won't matter how much you started with or how much higher the solution was heated.  When the solution cools to 20C it will hold 0.22g/100mL of solvent (water).\n\nSo if you start with 1.75g and 0.22g remain in solution, the amount crystallized at 20C will be the difference, 1.53g.