Is it true that hot water freezes faster than cold water?
408269
It actually can be, believe it or not.  It has to do with hydrogen bonds.  Water exhibits very strong hydrogen bonding due to its polarity, and in order to freeze, these hydrogen bonds in liquid water must be broken.  In hot water, more of these bonds are already broken, so a quick drop in temperature could allow the water to freeze before the hydrogen bonds reform.\n\nNote that this is strictly a kinetic or time-based effect.  Thermodynamics dictates that cold water will freeze faster since a smaller energy drop is required, but in some cases it is entropically favored for hot water to freeze faster.\n\nAlso note that stirring the water vigorously will also break hyrdogen bonds, so stirred cold water will almost always freeze before stirred hot water.  You will only observe the phenomenon of interest when the water is fairly pure and undisturbed, and the temperature drop is rapid enough.\n\nWe discussed this very problem in my graduate-level thermodynamics class.
237724
Infact, FLOWING water does freeze. but FLOWING WATER cannot freeze completely at 32 degrees providing it is attinaing warmth from somewhaere else. If you check the temp of a glass of ice water. It is 32 degrees but it is not completely frozen! 32 degrees is when ice begins to form &/or can sustain itself. The only reason your ice melts is because the water temp surrounding the ice is conducting the heat of the room which in turn tries to rise the water temp. While the ice is trying to hold the temp @ 32 degrees. Eventually the ice will melt; it releases cold in the form of water, to cool the water surrounding it. But because the warmth of the room is indefinate, the ice will eventually melt away as it is unable to hold the temp. Now if you put you ice water in a freezer that's set at 32 degrees. Your water will freeze. Because the water is no longer drawing the energy it needs to sustain its heat so the ice wins and freezes the water. \nSo how the heck does this pertain to rivers and moving water?\nMoving water is gaining warmth from the ground and the air. but becaue its moveing the temp of 32 degrees is not easily sustained so the ice melts and refreezes as it travels, because the weather changes and temps change ect. The only way to freeze moving water it to either:\n1. Have it be so cold that the water nearly immidiatly freezes (well below zero) or \n2. Have a sustained temp of below 32 for several hundreds of miles. \nNow if you put the water in a water rocker and put it in the fridge at 32 degrees it will freeze solid at some point because the temp is sustained and really how long it takes for it to freeze is the ultimate question. which depends entirely on the temp.\n-hope that helps
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.
104094
cold make stuff get bigger but hot water makes stuff constrict
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 ;)
541181
See this answer.  Dig into the citations for the reference articles in them.  The second also has references.\n\nHot freezes faster in many cases, given certain controls such as same amount of water, same size and shape container, standard pressure etc.  There  is at least one experiment showing that water at 90 degrees C will freeze quicker than water at 18 degrees C.  This is significant since one side is quite close to boiling and the other is basically room temperature.\n\nIf you are not a high school student, I would look up linear programming ( a branch of algebra not computer science) and develop a sensitivity analysis to determine the impact of various effects.
209676
Neither can freeze.  Boiling water is 200+ degrees F.  Room temp is roughly 70 degress F.  Now, if you meant does something at room temp freeze faster than something that is at boiling (water), then the answer is, in general, yes.
926439
fresh water freezes faster...ps, i gave you best answer on a question
419356
I will take a stab at it.  I am guessing it is because water has more degrees of freedom.  In the liquid there is also rotational degrees of freedom to absorb energy that the solid ice does not have.\n\nTo Neil, the formulas are for heat capacity and have nothing to do with the way something is heated, only the amount of energy that it takes.\n\nNor does it have anything to do with Newton's law of cooling.
292815
The answer is no and sort of.\n\nWater at 38 degrees (i.e. from the refrigerator) will freeze significantly faster (10 to 15 minutes faster) than hot water from the tap (125 degrees).  This is the range of temps most people are going to be dealing with.\n\nHowever, water at 190 degrees will freeze faster than water at 140 degrees.  The main reason is that more of the hotter water will evaporate before reaching freezing temps, so the ice cubes are significantly smaller - about 7/8ths the size of the cooler water.  Putting plastic wrap over the heated water reduced the time differential significantly.  \n\nI think the moral of this story is that you can get nearly any result you want by manipulating the conditions correctly.\n\nAlso, I feel the need to correct the second answer above.  Cooling is the process of slowing down molecular movement, not speeding it up.
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.
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.
888554
Strangely enough, the HOT water would freeze first.  There is a chemical explanation for this.
53097
well, ice is solid, water is liquid, and air is gas, and the potential energy increases as the stages change.  in other words, air is the warmest, water next, and ice last.  air being the warmest will warm up the ice faster and therefore melt it quicker.\n\nthe only reason that i can see why it'd be in water is if there's been a sudden change in temperature and the water is still warm but the air is cooler (cold front after a week of mid 60s or 70s weather).
77192
No, adding salt does not make water boil more quickly. The colligative properties of water talk about freezing point depression and boiling point elevation. Water will reach a higher temperature before it boils when it contains salt (or any other dissolved substance).\n\nNucleation is a reasonable point, though. In reality, it's probably going to be hard to detect much of a difference. If you're cooking at high altitudes and you add salt to try to make the water boil faster, you're working against yourself.
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.
135812
Well for an eight year old....(sounds like an intelligent one to me though)... The reason water freezes slower is because the particles of salt and sugar get in the way of water making a ice crystal.  Salt takes longer because when dissolved it "ionizes" or breaks apart into 2 particles while sugar remains as one.  Salt having two particles it is able to disturb more molecules of water from making ice crystals. I hope that helps! It excites me to here a child of such a young age interested in such things.