Why does hot water formed into ice faster than normal temperature water when put together in a freezer?
I don’t think it does. Have you tried it?
If it does, it’s probably because a lot of the hot water evaporates, so there is less water to form into ice.
its strange but true…but why? hmm…
Actually, it doesn’t happen (at least not under normal conditions)… Cecil commented on this already:
It’s often called the Mpemba effect, there are a large number of factors involved, including heat loss by conduction on a bed of ice crytals, dissolved gases, evaporative cooling, cooling curves, reduction of volume through evaporation etc.
This particular Urban Legend has been around since at least the 1960’s as I can attest to it being told to me by a fellow high school student in or around 1961-62. And I believed it until sometime in the 1990’s.
It doesn’t.
In an experiment it might appear to do so, but that’s because much of the hot water evaporated, and therefore freezed faster.
Why do you say this? How did you find out?
I put scalding* hot water in a cup and cool water in
a cup and put both in a freezer.
The hot water was forming ice crystals that floated
to the top-center, before the cool water.
The cool water froze-over. (Top ice.) While the formerly
hot water had a small iceberg floating in it.
While I can’t be certain WHICH froze solid first, the
cool water was ahead each time I checked.
In the end, the cool water had a flat top and the
hot water froze into a bumpy top due to the iceberg
developing.
*Scalding? Yep, I tested it with my finger.
While this is not evidence, I’ve seen two seperate TV shows showing how ice at rinks are made.
Both of them said that the re-surfacer (aka Zamboni) uses hot water because it has less oxygen, therefore freezes faster.
I am not saying this is factual, just throwing it out there…
The warm water isn’t used because it has less O2 or freezes faster, it melts the top layer a bit so the new layer bonds better and don’t chip off as easy. Quote from this page: “The hot water loosens the crystal structure of the old ice underneath, so the new ice will form a solid bond with the old ice, instead of a separate layer that chips off easily”. The link shows how a zamboni works!
Also hot water DOES have less oxygen dissolved in it as hot water always does so when it refreazes it produces ice with no air bubbles that have percipitated out of it so it is harder and smoother for skaters. Thats why freezing hot water in ice cube trays makes it clear instead of cloudy… no dissolved oxygen.
It’s not truly an urban legend. Did you stop believing it because you did experiments?
under certain conditions hot water will freeze faster than cold.
Do a google search on the Mpemba effect (or click the link in my post above) - the search results will mostly be from academic sources.
It’s not specifically dissolved oxygen, it’s dissolved AIR in ice that can lead to bubbles. Nitrogen accounts for about 80% of the dissolved air in water - oxygen is a relatively minor contributor compared to nitrogen (1/4 the amount). You can dissapate dissolved gases from water by heating it, but they will dissolve back in pretty quickly as the water cools. You’ll loose a lot of the effect of heating water to get rid of bubbles if you then put it in small open compartments in the freezer exposed to cold air for half an hour. It’s the thin layering of water (and it’s purity) that’s mostly to account for clear and even ice; hence the zamboni’s layering technique. Here’s a page describing how hard, clear ice is made. Back to the original question… after reading through the “Mpemba effect” page(first one in the list), it’s still quite clear that a set mass of hot water will technically NOT freeze faster than an equal mass of cold water given identical conditions. The Mpemb effect accounts for all the little “unfair” glitches in the freezing experiment; which seem to be what Genecola is asking for.
#1) Evaporation - REMOVES MASS resulting in less water for the “hot team” to freeze (blatant cheating:D)
#2) Supercooling - Acheived through very stringent lab conditions and equipment that rarely if ever happen in your freezer (very smooth, sealed glass containers, and a sudden plunge into freezing liquid chemicals is required)
#3) Convection - Only a theory of separated water layers that are unlikely to form in water an inch deep… the page it’s self casts doubt on the importance of convection.
#4) Dissolved gases - as described earlier have an effect but not a huge one. By the time the water is down to the freezing temp a lot of gas will have dissolved back into solution due to a rather high surface to volume ratio in an ice cube tray… the page mentions a lack of proof in this area.
#5) Conduction - More of the “hot team’s” solid container surface being in conact with the freezer floor due to it’s melting into it. Another case of cheating:D by giving one side a greater capacity to transfer heat than the other.
The top three conditions also only apply to getting the water down to the starting temp of the cold water faster; none help once the hot water is the same temp as the cold water. So these little loopholes seem to stack the deck unevenly as for a fair competition, but they can give explanations to some experiments. I only looked at the first Mpemba page… come on, it’s 4am!!:o
Well, sure, you could call it ‘cheating’ (I have no agenda here, so I’m not prepared to defend the Mpemba effect to the death), but you could just call it ‘reasons’ instead.
Sure, there’s loss through evaporation (although I can’t imagine it’s going to be a whole lot), sure, there’s better thermal conduction between a warm container and a frosted surface, but if you disallow these and all the other ‘reasons’, maybe you’re introducing unfair bias toward the ‘cold team’; nobody is saying that hot water freezes faster for no reason at all, that would be absurd.
This is pure BS. Water freezes because the temperature of the molecules reaches the “freezing point” of H20 for the given pressure and volume of the system.
Think of it as a race. The warmer molecules have to lose more heat to reach the freezing point. They are thus “handicapped” compared to the colder molecules placed in the fridge. They will thus take longer to lose their heat and freeze than will the colder molecules, all other things being equal.