if the heat aways goes up....then why is always only the top-layer of the water frozen?
438051
Well i would like to answer this but it looks like its been taken care of.
310551
The water level will neither go up nor down.\nSuppose we have an ice cube of mass m floating in the water. In equilibrium, it will have to displace enough water to support its weight. It is V=m/d\nNext when the ice has melted, it turns into water of volume: V= m/d! exactly the same volume as it displaced before. So the added volume is the same, so the level of the water will not change.
582707
Ice takes up more volume than water, so the pressure is higher when you have the water in the freezer.  Crystals form at lower energies where entropy is lower, and higher pressure is equivalent to higher energy, so water remains a liquid.\n\nWhen you open it the pressure is released.  Gas expanding cools the air (entropy again) thus making the surface of the water lower in energy and promoting crystalization.  Poke a hole in the bottle and try this and the crystals will form in the freezer before you open it.
1010626
Could be that different chemical compounds freeze at different temperatures.  Water freezes at a lower temperature than 36 degrees but not everything does.  That is also like why you put salt on ice to thaw it, it lowers the freezing point, so it has to be a lot colder before you get ice.
215641
Usually, when a pond freezes, it does not freeze totally solid.  Due to some rather nice properties of water, the pond will freeze from the top down leaving the fish with an area below the ice to swim around it.\n\nDue to fact that water expands when it freezes (because of the intermolecular forces at work), ice floats in liquid water.  Similarly, when pressure is applied to ice, it melts since it is trying to relieve the pressure on the system and this can be done by reducing the overall volume by melting.
731331
I've heard that its the boiling water that freezes first. \n\nI think because the water molecules are hot (i.e. they are moving fast) the energy (or heat) will escape (move to equilibrium with other items in the freezer) at a faster rate than the water molecules in colder cup of water. \n\nBut really I'm mostly guessing with my explanation.
858544
Because water expands when it freezes..\nTherefore ice is of larger volume than the water it originated from\ntherefore it is less dense..
745528
Interesting theory, however water expands when it freezes.  It has no problem melting under pressure.
415970
I don't have a scientific answer for you, except to say that's just how it works. You could say it's the same reason that water expands when it freezes, as opposed to almost everything else which contracts.
86483
Actually, Gonpatrick, the original question is quite correct: Unlike most substances, water does actually expand when it is cooled, over a narrow temperature range from about 4 degrees C to 0 degrees C (the freezing point.)  This is why water freezes from the top down: the cooler water that is closer to freezing is less dense than, and so floats above, slightly warmer water.  (Above 4 degrees C, water expands when it is heated just like most other substances.) When the water freezes it expands some more, which is why ice floats.\n\nThe reason why it does this has to do with the way water molecules are put together.  The two hydrogens and one oxygen in H2O are assembled in a triangular pattern, with one part of the molecule more positive and the other more negative.  Above 4 degrees C, the molecules move freely around each other, but when it gets close to its freezing temp, the molecules start to align themselves with the positive part of one molecule near the negative part of another, ultimately forming, when it freezes, a hexagonal pattern.  This arrangement takes up more room than when the molecules are free to move around.
432623
It depends on the temperature of the water and the air but if they are the same, then the ice in the water will melt faster because water is a better conductor for heat.
260171
It isn't air! When water freezes all dissolved gases & other matter are not included!!! \n\nThe hydrogen bonds that form when water freezes creates an open structure. There is simply nothing in between those spaces.\n\nWe are talking about molecular structure, things at this level are so tiny that even thinking about what is in between is silly.\n\nIf there is anything between the spaces it is probably interstitial water molecules (those not hydrogen bonded inside the crystalline lattice structure - think of them as loose molecules of water).\n\nIce floats on water because it has expanded. That is all. Not because of what is in between the "spaces".\n\nSee, when you increase the surface area but have the same number of molecules present, you cause the object to become less dense. (it's less tightly packed...things that are tightly packed for their size are said to be more dense.)
873711
Not quite right.  It is most dense at 4 degrees C.  If it didn't, the water would freeze from the bottom up.  As it approaches 0 degrees, it becomes less dense and rises above the more dense warmer water and freezes on the surface and goes down.  Otherwise, fish would be on top of the ice and die after it froze.
807422
When water freezes, it expands because the molecules form into a crystal lattice. The expansion causes ice to be less dense than liquid water and as a result, it floats.
236269
Because the atoms in heated water are farther apart.  It actually makes the water less dense.  It then becomes easier to freeze less dense liquid.
499459
A very good question.\n\nAlmost all common chemical will contract upon freezing, but not water. \nThe special hydrogen bonding that forces the water molecule to be very close to eacher other in liquid phase.\n\nThe molecule of HOH is not straight, but in a V shape. About 105 degree.\nIn liquid phase the V shape can over lap each other. Go look up the water structure at\nhttp://www.chem1.com/acad/sci/aboutwater.html\n\nDuring freezing, the water molecule are force to line up, and the V shape molecule are line up side by side and no longer over lap.  This takes more room. So it expands.\n\nGo look up the ice molecule structure at http://www.uwgb.edu/dutchs/PETROLGY/Ice%20Structure.HTM\n\nIts not easy to see the true structure, but these will at least gives you a picture.\n\nKeep asking questions, enjoy.
383320
the idea isn't that water can't heat up when it boils at low pressure, but that it doesn't have to. no matter what temperature something is, its molecules are moving somewhat, and some of them escape as a gas. also, any gas always is condensing into a liquid or solid. when pressure and tempurature are constant, these processes reach equilibrium where they cancel each other out. at high temperature, more gasses escape, and at low pressure, less gases return to liquid. so at somewhat low temperature and relativly lower pressure, even though few gases relatively escape, even fewer return to liquid, so the net effect is that the liquid evaporates at low temperature. if the temperature were raised, it would boil even faster.