Making ice with hot water.

As most readers of the Straight Dope probably know is that there is a controversy surrounding the idea that hot water freezes faster than cold water.

I have always supposed that the reason is that a small amount of water might evaporate from a hot sample, thereby requiring less heat loss to freeze it. Since there is more heat loss the greater the difference in temperature, and the amount of heat loss required for a change of state is so much higher than that required to simply cool off one degree, this seemed possible.

My question however is…

Why is this still a controversy. I have read discussions of this topic from chemists and physicists who are clueless about the answer. It would seem it would be relatively easy to check out and put to rest.

Certainly not easy with ice cube trays in the Amana and a diet scale, but with lab equipment in the average college, it would seem easy to pull off.

Is there something about this I don’t understand that makes it difficult to check out experimentally, or has an answer I don’t know about been found.


Has it been ignored because there’s no money in it. (my guess.)

It’s not a controversy around here. Cecil covered it already, and answered the question quite adequately, IIRC. No, hot water does NOT freeze faster than cold water. It’s in the archive somewhere, I don’t feel like looking it up. Feel free to if you want to, though something tells me that if yiou haven’t already you won’t even now…

Jason R Remy

“No amount of legislation can solve America’s problems.”
– Jimmy Carter (1980)

Come on ,gill, think it out. Here are two identical samples of water in identical containers. There is one diference, sample A is at 50* B at 20*
(=degrees celsius) put both in identical feezing chambers, with identical temperatures at or below 0 Now which one is going to freeze first?
What do you mean “theres no money in it?” Let me introduce you to the Lil Igloo, the newest inovation in ice making machines. Oh sure it may cost more, but the increase in speed alone is worth the price.With its inovative flash heated steaming hot water it makes ice making almost fun again.

“Pardon me while I have a strange interlude.”-Marx

KID gilligan? Registerd on the 24th? Ouch, there is something sharp in my mouth. I been had.

“Pardon me while I have a strange interlude.”-Marx - Which freezes faster, hot water or cold water?

Thank you all for your rapid replies, but after the first rereading of Cecil’s column on the subject, it seemed clear that the hot water theory was all wet.

After a second rereading, I still think I note a certain amount of equivocation.

The article cited seems to imply that the very hot water did freeze faster, and only SUPPOSES that evaporation was to blame.

It would seem that someone could do the math (using known constants regarding heat lost through evaporation, heat loss required to freeze a given mass of H2O, etc) to calculate whether or not that is a valid supposition.

Does anyone know of anyone who has gone to this much trouble?

This is another perpetually discussed topic on alt.folklore.urban.

The SciAm article Cecil refers to in the link given by Kat is:

Jearl Walker in The AmateurScientist, Scientific American, Vol. 237, No. 3, pp 246-257; September, 1977

Another reference recommended by the AFU FAQ is:

“The Freezing of Hot and Cold Water”, G.S. Kell in American Journal of Physics, Vol. 37, No. 5, pp 564-565; May, 1969.

Isn’t the reason behind this question to determine whether you should connect an icemaker to hot water or cold? A salesman in a Sears store told my aunt to connect her icemaker to hot water, so it would freeze faster. My first reaction was “huh”, so I did a little experiment.
Take two ice cube trays, one with hot and one with cold, stick 'em in the freezer, and see which freezes faster.
I did this several times. The result;
Cold water freezes faster, every time, by a pretty good margin.
Has anyone had different results?
BTW; the hot water did seem to make clearer ice.

Work like you don’t need the money…
Love like you’ve never been hurt…
Dance like nobody’s watching! …(Paraphrased)

There are many “gedanken” experiments that one can do in the comfort of one’s easy chair to prove that hot water CANNOT under any circumstances freeze faster than cold water. I should leave it as an exercise to you people to come up with some yourselves.

But I’ll start out with two:

Lets suppose that the converse occurs, hot water freezes first. Then at some point in the process, the “hot”: water will have “passed” the cold water in its race toward freezing (it freezes first by hypothesis). But wait…, now the cold water is hotter, so now it must freeze first. Since it freezes first, it must start cooling faster than the other, so it passes the previous hotter water in its race to freezing… but wait, now the other one is hotter, oh the hell with it. By the way, how does the first cold water know that it has been passed in temperature and must speed up? Oh the hell with it again.

Number two–Try this thought experiment…

Take a containers of water of temperature “high”. Put it in a perfectly functioning freezer. (This must be stated because halfwits will say… "Yes but, what if the freezer doesn’t work right, or what if it is full of warm meat…) So, to continue…This container of water will freeze after a certain period of time say “x” minutes.

Now, before it freezes, after some arbitrary interval less than “x”, say, “y” minutes (y<x), it will be at some lower temperature . Lets call that temperature “low” (it is in the perfectly functioning freezer remember). This temperature after time “x-y”, “low”, is less than the starting temperature of value “high” the temperature of the water the instant it was placed in the freezer.

Prepare a container of water identical in all respects to the first container. (This is legal in a thougth experiment.) It has a temperature “high” which is higher than the current value of the first container, now of value “low”. Put it in the freezer. It will freeze in “x” minutes. “X” > "X-Y for all positive values of “y”

The vogue of thinking hot water freezes first is popular among scientific illiterates. Even the mainstream media falls for this. There was an article in the Detroit Free Press a few years back about the Zamboni Ice machines (the weird contraptions seen between hockey periods which clean up the ice). The article stated that hot water was used because it froze faster than cold water. Of course a clear impossibility. But it is common for people to think this. The “shock” of the hot water causes the faster freezing is the usual reason given. Where this scientific “shock principle” came from eludes me. Anyway, why is hot water used in zambonis? Anyone who ice skates knows the answer. Cold water will freeze too FAST!!! It will not have the opportunity to melt imperfections in the ice (skate divots, etc.) like hot water will have. Hot water will give a glass surface to the ice, perfect for skating. Cold water may leave skate marks and divots, not pleasing to the eye, and possibly dangerous, especially to on the edge skaters like hocky players.

Hey, that’s what I said. :slight_smile: