does water freeze faster at a lower temperature?
609909
The effect is known as Newton's Law of Cooling.  The rate of change in temperature is related by a differential equation to the difference in the liquid's temp and the temp of the atmosphere.  A warmer solution will have a larger rate of cooling.  Which one actually freezes faster in terms of time, not rate, is different.
1163536
The definition of freezing is that they reach 0C, not that they turn to a solid, that is a separate step.  Hot water pipes and cold water pipes, both in an identical freezing environment will cool down at different rates because the higher the temperature gradient or difference, the faster the rate of cooling.  So hot water will cool faster to 0 than cold water, although cold water will form ice faster since overall it requires less heat overall to be removed to freeze.\nNote that practically the hot pipe will take longer to freeze solid since there simply needs to be more energy removed to get the solid.  This question is normally asked theoretically to demonstrate (or trick a student) to teach the lesson about how larger temperature gradient have a higher cooling speed relative to the lower temperature gradient.  It depends on the reason for asking this question.\n\nNote that the Mpemba effect, while it has been observed, is only under specific experimental conditions and is far from a general phenomenon and not general enough to effect the average set of pipes in the average house basement.
656503
It doesn't.  Ice melts more slowly on a colder surface because when ice melts it must draw heat from the surrounding environment, and when there is less heat available it takes longer.\n\n____________\nEdit: as a college science major, I can tell you it simply doesn't work that way.  However, there are a number of factors besides temperature that effect ice melting.  For example, if the piece of ice on the colder block was considerably thinner than the ice on the warmer block the one on the colder block might still melt faster.  In biology, we sometimes melt small amounts of liquid on ice because bad things happen if they get too warm, and two microliters of frozen liquid on ice generally melts faster than ten mililiters in warm (about 98˚F) water.\n\nAnother factor that effects melting point is solutes dissolved in the water before it was frozen.  Salt water freezes at a lower temperature, and consequently melts at a lower temperature, than pure water (that's why the salt the roads in the winter).  If there were a lot of salt dissolved in the piece of ice on the cold block, then depending on the temperatures of the two blocks, the one on the cold block might melt faster.\n\nIt's also possible that one or both pieces of ice weren't water at all.  There are plenty of clear liquids out there that melt at various temperatures.  A compound with a lower freezing point will tend to melt faster, possibly even at a lower temperature.\n\nAnother factor is the starting temperature of the ice.  In one of the biology labs at my school we have a freezer that's at -80˚C, and the normal ones at 4˚C.  If you take a piece of ice out of the -80˚C freezer and one out of the 4˚C freezer, they're both frozen, so they're both ice, but the one at -80 is a lot colder, and is going to take a lot longer to melt, even at a warmer temperature, because it has to warm back up to 0˚C before it can even start to melt.\n\nBut, of course, the obvious explanation is that either your teacher lied to you, or you lost track of which block was which at some point in the demo.
926439
fresh water freezes faster...ps, i gave you best answer on a question
496282
No.  You would have to heat the cold water up to the temperature that the hot water is at and then go past it to get to the boiling point.  It works in reverse when freezing.  Hot water will not freeze faster than cold, because you have to remove heat just to get to the point the cold water is already at.\n\nThe cool part is you can do this experiment at home.  Put two pans on to boil, one with cold the other with hot, and see which one boils first.  You don't have to take my word for it.
10515
water freezes at 32 F.  When you add other substances to water, you create a soliable compound and the solution takes on some of the quality of the other substance.  Adding salt or sugar prevents the solution from freezing at 32 F. Juices or bullion cubes would work in a similar manner.  if you're going camping, sleep with your water in your sleeping bag ;)
360729
It doesn't.  The t(exp 4)(temperature difference to the 4th power) law works here.  The higher temperature water will cool faster than the cooler water, however, when it reaches the temperature that the cooler water was in in the first place, it will cool at the same rate the cooler water cooled with.
434026
If you place a glass of hot water in an ice box it will actually freeze faster than a glass of cold water. \n The reason is that the temperature difference makes the water circulate in the warm glass transfering the heat loss evenly through the contents, in cold water the outside freezes first which insulates the inside from heat transfer keeping the center liquid.\n Try it, you'll see.
241754
Thermal intertia.  It works the other way too, cold water boils quicker than hot water.  The reason is when hot water is placed into the ice cube tray it immediately begins cooling.  Then when you put it into the freezer it continues to accelerate more and more quickly to the low temp desired.  Cold water would begin warming as soon as it gets put into the tray and then you have to cool it back down (opposite direction heating takes more energy)
23033
If you were able to get the salt solution cold enough, it would freeze. However, if you put two ice trays side by side, one filled with water, the other filled with salt water, and chilled them to the point where both froze, the would both be the same temperature. However, once the cold was taken away, the salt solution would melt at a much lower temperature than the water only cubes.\n\nWhat salt does when added to water is decrease the temperature at which water will freeze -- as well as melt. How much the freezing/melting point is lowered depends on how much salt is added. The higher the concentration, the lower the freezing/melting point.
125319
The ice water will cool quicker.  The reason being, that the water will cover the entire surface area that you are trying to cool.  \n\nThat being said, it also won't last as long because it also has more surface area for the cooling to escape.
291269
Cold water has more dissolved gases in it than hot water.  Any dissolved solutes cause the freezing point of water to be lower than pure water with nothing dissolved in it.\n\nThis means if your power goes out in the wintertime and it is about 32 degrees F outside, the water in your hot water pipes is more likely to freeze than the water in your cold water pipes.  This is because the freezing point of the water in your hot water pipes is higher than the freezing point of the water in your cold water pipes.\n\nSpeed isn't being considered here.  The cooling process is assumed to be slow so that the pipes are in thermal equilibrium with surroundings.\n\nAlso check out this link.  It is from the Alaska Science Forum.  They can explain the water pipes problem more correctly than me and they have more personal experience with the phenomenon.\nhttp://www.gi.alaska.edu/ScienceForum/ASF4/440.html
60893
Sodium Chloride (NaCl), or salt, lowers the freezing point of water.  Putting salt on ice turns it back into water UNTIL the temps drop below the point where the salt water will freeze again which is between -9°C (15°F) and -21°C (-6°F) depending on the amount of salt suspened in the water.
288935
Fresh water freezes when the temperature of the water is 32*F and the pressure is normal atmospheric pressure. And then, if there is a heat loss for that fresh water, then it would freeze at lower pressures also. \nIf ice is at 32*F and there is a heat gain, it would melt at 32*F. Also, if at 32*F with no heat flow there is higher pressure, then ice would melt. (eg skiing. If you put your pressure on the skis, the ice/snow melts and becomes water so that you can ski)
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.
215770
depends on the ice...\n\nmany different types of ice in different states of being 'frozen' and at different temperatures and with\ndifferent degrees of purity of the water or other frozen substance...\n\nthe answer would be yes more often than no...
79685
No.  There was a time when people said it did because some dude in Africa was making ice cream and claimed that his ice cream froze faster if he heated it first, but that's because ice cream needs to congeal, and heating it boiled off much of the water, making it thicker to begin with.\n\nAnd it has been shown even since the time of the Greeks that water that has been boiled prior to freezing will freeze quicker due to the fact that boiling will remove dissolved gases from the liquid, but even that assumes you are comparing water that's been boiled and brought down to temperature versus water that has not been boiled.\n\nBut if you put water that's 8 degrees and water thats 80 degrees in a freezer, the 80 degree water, prior to freezing, will need to reach 8 degrees somewhere between here and there.  All the while, the 8 degree water has made substantial progress towards freezing.\n\nIt is true that hot water loses heat more quickly due to an increased driving force for heat loss, but this is a temporary thing.  As soon as the hotter water reaching the starting temperature of the cooler water, it has no "momentum" in losing heat, but it has lost a lot of time.