how come hot water freezes faster then cold water?
114884
Hot water does not freeze faster than cold, all conditions being the same, such as altitude, air pressure, and amount of cold applied to the water to make the water freeze.
213133
The cooler water will freeze faster.  The hotter water is the faster the molecules in it are moving and the more energy there is in the water.  Before water can freeze it needs to lose this energy.  Therefore the more energy it needs to lose the longer it takes to cool and the longer it takes to freeze.\n\nThe belief the boiling water freezes faster than cooler water is a popular misconception.\n\nHowever, it is true to say that boiling water (100 degrees C) will freeze slightly faster then almost boiling water (95 degrees c) but that's because considerably more of the boiling wtare will evaporate than the nearly boiling water and therefore there's less water remaining.\n\nThis probably explains why cyanne2ak is able to freak people out by throwing hot coffee at them - in very cold temps theere will be very rapid evapouration and as such far less of the coffee that leaves the cup will land on the 'victim' then would be the case with tap water.
844878
Gases are more soluble in cold water than hot.  So if you take cold water from the faucet and freeze it, the ice will usually be cloudy.  If you heat it up first--or better yet, boil it--then freeze it quickly, without letting it sit around and absorb more gas,  the ice will be clear.
494092
As any sane and decent person would expect, hot water out of the tap will boil faster than cold water out of the tap. However, water that has been boiled once and allowed to cool will boil faster than hot water out of the tap. That's because boiling gets rid of the dissolved oxygen usually found in water, making it easier for the water to boil the second time around.
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.
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.
384592
when you pour water on the ice, the ice has layer of water around it, but its still really cold. when the new water stays next to it, the ice cube freezes the water around it, if two ice cubes are touching, they will freeze the water between them and stick to eachother
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.
922727
The reason is that heat causes molecules to move faster - the cold slows them down. Think of it like molasses when it is cold it is really thick and flows slowly - but if you heat it up it thins out and would flow more easily. When molecules are heated they are easier to manipulate. I hope this helped.
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.
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.
379878
Density is the key property that determines whether or not a substance floats.  Ice floats because it is less dense than liquid water.  Why is ice less dense?  Because the water molecules in ice are arranged in a crystal lattice that spaces the molecules farther apart than when they are in the liquid state.  That is why ice floats.  \n\nBy the way, your initial statement that cold water is heavier than warm water is not exactly worded correctly.  It is more correct to say that cold water is denser than warm water, not heavier.
183968
when i was in 3rd grade i did onw on what freezes faster.... hot cold or salt water. actually got frist prize in the school science fair and 2 in district
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)
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.
629453
warm water dissolves ice faster than warm air because it can transfer and absorb heat faster than warm air of the same temperature
100228
The temp. between hot water and steam is a big difference. Say that steam is at 400 degrees F and hot water is 180 degrees F, steam will boil your hand faster then hot water.