Boiling Water...

[ChefSwartz]

I have heard from a couple of people that cold water boils faster than hot water.

I have also heard a tale that hot water freezes faster than cold water.

I find both of these tales very hard to believe. I have read the passage from "What Einstein told his Cook(Robert Wolke)" and he slams any notion of the validity in these claims. I would like to know another resource or two on this topic, that proves either thought.

I am not a psyicist but i know a little science. This seems like an impossibilty.

thanks

[Patrick S]

All other things being equal, the hotter water comes to a boil faster.

[Bob Musa]

reminds me of the burns and allen gag where gracie freezes boiling water so if she ever needed hot water she'd just defrost it.

[Patrick S]

Regarding hot water freezing faster than cold water -- yes, under certain conditions. Its called the Mpemba effect.

EDIT to clarify that the Mpemba effect is not necessarily hot water freezing faster than cold water, just a warmer volume of water freezing before a cooler volume. In other words, I doubt it could happen if the initial temperature differences are large.

Edited June 21, 2005 by Patrick S (log)

[slkinsey]

Think about it for a minute: You have two otherwise equal gallons of water sitting on the stove, one of them is 50 degrees F and the other is 100 degrees F. You turn on the fire below to bring them both up to the boil. Now, before the 50 degree water reaches the boiling point, it will also at some point along the way be 100 degrees F, right? So, how is the previously 50 degree and now 100 degree water any different from the water that started out at 100 degrees? The answer is that it they aren't different. They are equal. In order for the two volumes of 100 F water to be different there would have to be some kind of momentum effect in heat transfer whereby the colder water "builds up greater heat absorbing speed" compared to the warmer water. It's a nice idea, but thermal energy doesn't quite work that way.

The same applies in reverse with respect to freezing although, as Patrick points out, there are certain conditions that can cause warmer water to freeze more rapidly.

I think that the old saw about hot water freezing faster probably has its roots in two observations: Back in the days of metal ice trays freezers built up a thick layer of frost. If you filled the ice tray with hot water, it would melt through the frost, be closer to the cooling coil and therefore freeze more rapidly. Also, it's often the case in older buildings that uninsulated hot water pipes would be near a foundation wall and freeze in the winter whereas the cold water pipe, being further away from the frozen foundation, would not. This is what happened in our house when I was growing up in Boston. These are the kinds of things that made people think that hot water freezes faster, and I think that the notion that cold water boils faster just came about because it is the inverse.

[jackal10]

Hat water boils faster, but hot icecream freezes marginally faster than cold under some conditions as

a) it melts the ice between the bottom of the container and the icebox, so makes better thermal contact

b) The evaporation means less volume, so freezes faster.

Sam beat me to it

Edited June 21, 2005 by jackal10 (log)

[Tonyy13]

There was my food science instructor at Johnson and Wales in Providence, Paula Figoni, who has written several books, who told me first that warmer water would in fact, freeze quicker than cooler water. It had something to do with the convection of the water, and the lack of water bubbles in the final product. I guess the air that seperates the molecules of water having less cooling power than the other frozen molecules of water, and in fact, almost insulating the water molecules next to it. The warmer water freezes more clean and clear, making it freeze quicker. Who knows, I sure as heck don't, but I do know that my blast freezer is awesome, no matter whether or not you put in warm or cold product!!!!!

[Marlene]

Think about it for a minute:  You have two otherwise equal gallons of water sitting on the stove, one of them is 50 degrees F and the other is 100 degrees F.  You turn on the fire below to bring them both up to the boil.  Now, before the 50 degree water reaches the boiling point, it will also at some point along the way be 100 degrees F, right?  So, how is the previously 50 degree and now 100 degree water any different from the water that started out at 100 degrees?  The answer is that it they aren't different.  They are equal.  In order for the two volumes of 100 F water to be different there would have to be some kind of momentum effect in heat transfer whereby the colder water "builds up greater heat absorbing speed" compared to the warmer water.  It's a nice idea, but thermal energy doesn't quite work that way.

←

This sounds dangerously like one of those horrible math problems I could never solve in school. But I've always been of the impression that if I put a pot of hot water on the stove to boil for pasta, it will boil faster than if I put a pot of cold water on.

[snowangel]

I do know that if you take a pan of boiling water and toss it in the air when it's way sub-zero (F), the droplets freeze before they hit the ground or the deck. Water straight from the tap doesn't do it.

Kids love to watch this trick.

[JerzyMade]

I have heard from a couple of people that cold water boils faster than hot water.

I have also heard a tale that hot water freezes faster than cold water.

I find both of these tales very hard to believe. I have read the passage from "What Einstein told his Cook(Robert Wolke)" and he slams any notion of the validity in these claims. I would like to know another resource or two on this topic, that proves either thought.

I am not a psyicist but i know a little science. This seems like an impossibilty.

thanks

←

Honestly, all you need is a wristwatch to conduct your own experiment. I "suspect" that you won't be surprised by the outcome of the experiment. If your friends can accomplish the opposite they're on the short track to developing a perpetuum mobile.

[Jose Andres]

Regarding hot water freezing faster than cold water -- yes, under certain conditions. Its called the Mpemba effect.

EDIT to clarify that the Mpemba effect is not necessarily hot water freezing faster than cold water, just a warmer volume of water freezing before a cooler volume. In other words, I doubt it could happen if the initial temperature differences are large.

←

Thanks Patrick in your answer you clarify everything....................But Harold McGee also has a whole chapter on it.......And explains the reason behind it........

[Patrick S]

What is baffling is that apparently the Mpemba effect has been demonstrated in experiments that eliminate many of the mechanisms proposed to explain it. With respect to frost-melt-layer effect mentioned by Jackal, the FAQ I linked to states:

. . . one explanation for the Mpemba effect is that if the container is resting on a thin layer of frost, than the container holding the cold water will simply sit on the surface of the frost, while the container with the hot water will melt the frost, and then be sitting on the bottom of the freezer.  The hot water will then have better thermal contact with the cooling systems.  If the melted frost refreezes into an ice bridge between the freezer and the container, the thermal contact may be even better.

Obviously, even if this argument is true, it has fairly limited utility, since most scientific experiments are careful enough not to rest the container on a layer of frost in a freezer, but instead place the container on a thermal insulator, or in a cooling bath.  So while this proposed mechanism may or may not have some relevance to some home experiments, it's irrelevant for most published results.

And with respect to evaporation, there are experiments showing that the Mpemba effect is partly due to evaporation, but there are also experiments demonstrating the Mpemba effect even when both volumes of water are in closed containers which prevent the loss of mass by evaporation. The FAQ again:

While experiments show evaporation to be important [13], they do not show that it is the only mechanism behind the Mpemba effect.  A number of experimenters have argued that evaporation alone is insufficient to explain their results [5,9,12] -- in particular, the original experiment by Mpemba and Osborne measured the mass lost to evaporation, and found it substantially less that the amount predicted by Kell's calculations [5,9].  And most convincingly, an experiment by Wojciechowski observed the Mpemba effect in a closed container, where no mass was lost to evaporation.

The experiments exploring the role of dissolved gasses in the Mpemba effect also seem to be inconclusive. The FAQ cites a couple of older papers to the effect that the Mpemba effect doesn't appear when using degassed water, but then cites two more recent papers showing the gas content of the water doesn't have an effect.

I guess I can add the Mpemba effect to the list of things --like the two-slit experiment-- that remind me that the universe is stranger than I can imagine. Come to think of it, water is just surprisingly weird stuff in general, expanding when it freezes and so on.

EDIT to add the missing URL.

Edited June 22, 2005 by Patrick S (log)

[CharityCase]

This is slightly off-topic, but a landlady of mine always always always said to boil water for pasta with cold water. Using hot water was "dangerous" because hot water released toxins and mineral deposits from the plumbing.

[Patrick S]

Well, I know that hot water will dissolve and can hold more lead than cold water, and for that reason it is often advised not to use hot tap water for cooking. But I wonder if that matters if you have copper or PVC pipes? Dunno. . .

[ChefSwartz]

i also heard that about the lead, but it is only a concern in older houses.

[adegiulio]

Well, I know that hot water will dissolve and can hold more lead than cold water, and for that reason it is often advised not to use hot tap water for cooking. But I wonder if that matters if you have copper or PVC pipes? Dunno. . .

←

I know in my area, lead in solder is not allowed on potable water pipes...I use hot water for all cooking...

[Mayhaw Man]

This sounds dangerously like one of those horrible math problems I could never solve in school.  But I've always been of the impression that if I put a pot of hot water on the stove to boil for pasta, it will boil faster than if I put a pot of cold water on.

←

And if you put a couple of corks in it, there will be no sticking.

Of course, I bet you wish that I would put a cork in it.

[McDuff]

There was my food science instructor at Johnson and Wales in Providence, Paula Figoni,

←

Now, wasn't she something? How could you resist anybody who described a properly domed muffin as "perky."

And that collection of rancid fats and flours? Did you ever......?