[Joe L. Ogan (OP)]

Will hot water ever freeze faster than cold water.  If it does, why does it freeze faster than cold water?  Thanks for comments.  Joe L. Ogan

[RD]

Try searching for "Mpemba".

[Joe L. Ogan (OP)]

Yes, I am familiar with this URL but there appears to be some uncertainty about "Why" hot water freezes faster than cold water.  Do you know?  Thanks for comments.  Joe L. Ogan

[lightarrow]

Hot water can freeze faster than cold water in a lot of ways:
1. Put hot water inside a freezer, while put cold water inside a fridge   []
2. Allow hot water to vaporize so that a little amount of water will be really refrigerated, it will freeze faster than a large amount of cold water   []
...
...
explore the many possibilities.

Hot water cannot freeze faster than cold water!

What's happened to schools/colleges in the last years?  []

[Joe L. Ogan (OP)]

The fact that hot water will freeze faster than cold water is an established fact.  The reason "WHY" has never been established.  Thanks for comments.  Joe L. Ogan

[lightarrow]

An established fact by who? Where are scientific papers about that? Where is written in physics books? Which are the universities or the physics professors at university who claim this?

[Joe L. Ogan (OP)]

Look at Mpemba physics effect.  Thanks for comments.  Joe L. Ogan

[tommya300]

.
Wow Whoo wee. Sorry Lightarrow I have jumped before looking to many times and needed people to slap the back of my head and tell me more then once, thanks you all, and I hope I can help here!

 I have seen and did an experiment using a glacial substance, relating to this, but it was a long time and is foggy to remember. I do remember graphing delta Temp vs. time and the surprising thing was the hotter water lost heat faster then the cooler water over time. I know that is not what was asked here.

So I searched through allot of things, including the suggested, Mpemba physics effect, which I just learned here, and would of never knew it if it were not for this Site and all of you people.
Thank You Joe and RD...
I read that it is easier to explain that water melts at 32 F than it is to say it freezes at 32 F.

Special conditions are the key.
Changing liquid water to a solid ice form, I read that ice crystallization starts at 40 degrees F.
 I also read that super cooling water to below 32 F it can still be a liquid and then flash freeze to a solid.
Conditions:
This Question needs conditions to place any definite answer to it.

I read that there is "no one Mechanism" can cover all the conditions and give an absolute result.
Mpemba physics effect is the closest and the most recognized condition that the science communities can see yet!

I drink my sodas without ice but at temperatures as close to 32 F as I can or even from a bottle
I think, in my younger day, reading a beer label, Michelob beer label suggests to serve the brew at 42 degrees; they may be observing the frosty phenomena? If I opened a can of beer that was cold enough a slushy ice would form in a glass as I poured it out. Oh yea that happened when I put salt in the ice of my cooler and then stuck the cans of beverage and waited an hour or so.


Does anyone still stick a hot poker in their Yard or Mug of beer? Hot beer?

 Stumbling again I found a U-Cal has a write-up that can help here.

http://math.ucr.edu/home/baez/physics/General/hot_water.html [Links inactive - To make links active and clickable, login or click here to register]
.

[tommya300]

An exhibit of conditional freezing, ice solid forming before your very eyes

[hotdigittydogger]

I did the experiment... cold water froze first.  Try it yourself.  Why would anyone think hot water freezes faster?  Let's give it a quick thought.  If you start with water that is 1 degree above freezing, and another that is 30 degrees above freezing, is it not common sense that the water that only needs to drop 1 degree will do so faster than that which needs to drop 30?

[Joe L. Ogan (OP)]

Well, Aristotle, Descartes and many others have performed the experiment and their hot water froze first.  Later experiments have verified the fact.  Please look at Mpemba.  Thanks for comments.  Joe L. Ogan

[lightarrow]

To the school-didn't-teach-us-anything fan: if water at 40°F takes 1 minute to go down to 32°F and freezes, water at 41°F will need x time to go down to 40°F and then 1 minute to freeze. Do you mean that x is a negative value?

[Joe L. Ogan (OP)]

I am not trying to prove the phenomenon.  It has already been proven!  I am trying to find out "WHY" it works that way.  Thanks for comments.  Joe L. Ogan

[tommya300]

I am not trying to prove the phenomenon.  It has already been proven!  I am trying to find out "WHY" it works that way.  Thanks for comments.  Joe L. Ogan

"JLO'n'Mpemba" physics effect, a catchy label for the future physics books discribing the phenomenon and the reason why.

[tommya300]

Producing a miniature weather pattern:
Steamy energetic water, in  a container, producing water vapors, is placed in a freezer.
The surface of the water in the container is cooling as the vapors escape.
But not all water vapors are lost, some condense and circulate above in a cycle to attempt to gain a lattice crystal structure, precipitates, dropping to the surface and transfers the exchange of heat.
When the water surface reaches its highest density the lattice crystallization begins at the condensed vapor level  and begins to displace the warm water below it. As this happens water begins to freeze at the surface first.
It is the vapors of the hot water creating an additional heat sink.
Note it is slushy not solid ice.
The other room temperature water does not have the abundance of energetic water vapors to do this extra heat sink exchange

[JP]

I am not trying to prove the phenomenon.  It has already been proven!  I am trying to find out "WHY" it works that way.  Thanks for comments.  Joe L. Ogan

"Proven" wouldn't be the phrase I'd use.  It seems that in certain cases, you can get hotter water to freeze faster than colder water, though this isn't the case all the time.  Clearly, if average temperature is the only factor that matters (i.e. if the hot and cold water always have an even distribution of temperature, particulates, etc. throughout), then Lightarrow's argument holds: hot water first has to take time to cool to the cold water temperature, and then it takes the same time as the cold water did to freeze, so it can't possibly win the race to freeze first.  The problem is that apparently temperature isn't the only factor that matters, but that makes coming up with a good model difficult, since modeling water's exact behavior is complicated. 

The explanation that makes the most sense to me is that water isn't even in temperature throughout: hot water tends to rise and cold water to sink.  This can cause cooling to proceed at a faster rate than expected due to convection currents.  When the hot water reaches the cold water's starting temperature, it might have more hot water at the top and cold water at the bottom due to these currents than the cold water did when it started.  This will cause it to take less time to go from "cold" to freezing than the cold water does. 

But modeling and experimenting to test this are both very complicated, so the effect isn't well understood.  Usually people just throw out the fact that "hot water freezes faster than cold water," which isn't true.  It can do so under certain conditions, but it's not a general rule.

Edit: I see that the link tommya300 pretty much says the same thing I do, but in better detail.

[Joe L. Ogan (OP)]

Producing a miniature weather pattern:
Steamy energetic water, in  a container, producing water vapors, is placed in a freezer.
The surface of the water in the container is cooling as the vapors escape.
But not all water vapors are lost, some condense and circulate above in a cycle to attempt to gain a lattice crystal structure, precipitates, dropping to the surface and transfers the exchange of heat.
When the water surface reaches its highest density the lattice crystallization begins at the condensed vapor level  and begins to displace the warm water below it. As this happens water begins to freeze at the surface first.
It is the vapors of the hot water creating an additional heat sink.
Note it is slushy not solid ice.
The other room temperature water does not have the abundance of energetic water vapors to do this extra heat sink exchange. 

This is the most logical explanation that I have seen in regard to the phenomenon.  Have you performed experiments to substantiate your conclusions?  If so, I believe you should write it up and submit it for consideration.  This is not a new subject.  I remember reading about it many years ago.  Thanks for comments.  Joe L. Ogan

[Mootle]

You might find this http://link [Links inactive - To make links active and clickable, login or click here to register] of interest.

You would be forgiven for thinking that water is pretty simple, when in fact water is really tricky stuff, it literally has hundreds on known properties. Some of these properties are more readily measured than others. This makes it is very difficult to be sure that you are comparing apples for apples, which goes someway to explain why this dilemma has vexed folk for so long.

However, if you start with two identical samples of water and expose them to identical conditions, and then apply heat to one of the samples, it would be the cooler of the two samples which goes on to freeze first, every time!

[Joe L. Ogan (OP)]

Yes, I am aware that it does not happen every time.  In fact, one may well say that it requires special arrangements for it to occur at all.  But the fact that it does occur is very intriguing to me and always has been.  When I first heard it, I did not believe it at all but the evidence is too much for it not to happen.  Thanks for comments.  Joe L. Ogan

[tommya300]

Producing a miniature weather pattern:
Steamy energetic water, in a container, producing water vapors, is placed in a freezer.
The surface of the water in the container is cooling as the vapors escape.
But not all water vapors are lost, some condense and circulate above in a cycle to attempt to gain a lattice crystal structure, precipitates, dropping to the surface and transfers the exchange of heat.
When the water surface reaches its highest density the lattice crystallization begins at the condensed vapor level and begins to displace the warm water below it. As this happens water begins to freeze at the surface first.
It is the vapors of the hot water creating an additional heat sink.
Note it is slushy not solid ice.
The other room temperature water does not have the abundance of energetic water vapors to do this extra heat sink exchange. 

This is the most logical explanation that I have seen in regard to the phenomenon.  Have you performed experiments to substantiate your conclusions?  If so, I believe you should write it up and submit it for consideration.  This is not a new subject.  I remember reading about it many years ago.  Thanks for comments.  Joe L. Ogan

Joe I do not have access to lab equipment anymore.
I have not the finances to get my own equipment.
The thermal measuring equipment can not make contact with any parts of the model.

IR camera is needed to focus into the center of the vapor front.
Like trying to take a picture of the inside of a cloud.
Hi tech equipment something like miniature Halographic Doppler radar imaging. If there is such a thing.
I think the solution to the question should be viewed from meteorological aspect, combined with thermal sciences of the properties of water as each important stage of the process, can be observed.
After your question on why it works I said the catchy name for the phenomenon JLO'n 
So I searched the net and read about water as it interacts in the air. I stumbled on a few edu articles    

"JLO'n'Mpemba" physics effect, a catchy label for the future physics books describing the phenomenon and the reason why.
.
If this were to become a solution, hope the proceeds go to help the children, tomorrows future.

[lightarrow]

I am not trying to prove the phenomenon.  It has already been proven!  I am trying to find out "WHY" it works that way.  Thanks for comments.  Joe L. Ogan

No, you don't have to prove anything, you only have to answer the question I asked in my previous post.
About the explanations of the convective currents: ok, very nice. But then it's not "hot water freezes faster than cold water", it's: "moving water freezes faster than stationary water".
It's like if I said: "brunettes get more money from their husbands than blondes", but then one says: "ah yes, but *those* brunettes have much more rich husbands"  []

Are we talking about physics or about cabaret here?

[Joe L. Ogan (OP)]

I see that you are never going to give up on this topic, lightarrow.  Where have you been that you have never heard about this before?  It is not a new topic.  It has been around for years and years.  Thanks for comments.  Joe L. Ogan

[Geezer]

Are we talking about physics or about cabaret here?

I'll come if you have any free tickets. Who's in the lineup?  []

[lightarrow]

I see that you are never going to give up on this topic, lightarrow.  Where have you been that you have never heard about this before?  It is not a new topic.  It has been around for years and years.  Thanks for comments.  Joe L. Ogan

It's just this to make me nervous: people shoud understand, after some time. Another thing that makes me nervous is the fact people seems to become more and more prone to be convinced by false science year after year. Will we arrive to the point that everyone will believe on its personal theory, and science will be totally deleted? Science must be precise, otherwise it would be better to throw it away.

[Joe L. Ogan (OP)]

Do you think that this is false science?  Have you read Mpemba?  Ask some of the other guys.  It appears that most are familiar with the topic.  Thanks for comments.  Joe L. Ogan

[lightarrow]

Yes, I think it's false science, and dangerous, since people around seems to learn less and less from schools and so it's more easy to influence with wrong facts.

[rosy]

Lightarrow.

I think you are a bit too sure of yourself. There are lots of perfectly plausible explanations why, under some circumstances, a container of water that started out hotter might end up freezing faster than an otherwise identical container that started out colder.

I don't know, from personal experience, whether such conditions actually exist, but you are trying to apply thermodynamics in an inappropriately simplified form for the situation described.

If the water were at the same temperature throughout the container (top to bottom), it would be valid to assume that the container with the higher temperature must pass through a state with the same temperature as the cooler one started at, that this would take time, and that therefore the hotter sample must take longer to cool.

However, since water does -not- cool at a uniform temperature throughout its bulk, due to convection currents and to the fact that the rate at which heat is lost need not be constant in all directions (and in a freezer will certainly not be so).

No-one is claiming that hot water always freezes faster than cold water, but that under certain circumstances it could really is not the immediately impossible paradox it looks at first sight.

Whether or not the products of modern schooling are excessively inclined to believe "false science" is completely both irrelevant and uncalled for in this context*.

Your attitude to this question smacks, to me, of not knowing enough about the potential complexities of this situation to realise you might want to consider them.

*I don't know where you come from (ETA - having looked at your profile, it appears you're from/currently based in Italy), but my mother, now in her 50s, studied no science at school (England) except for human biology after she was 14. I doubt my brother, now 21, who studied at least some physcis, chemistry and biology compulsorily to 16 knows less science.. even if he doesn't really know enough to do anything meaningful with it.

[tommya300]

What is false science?
How is it that many independently proved facts, can be considered false?
Designating conditions of an experiment, recording events throughout the experiment, providing the results that reoccurs in redundancy over and over again.

[lightarrow]

Lightarrow.

I think you are a bit too sure of yourself. There are lots of perfectly plausible explanations why, under some circumstances, a container of water that started out hotter might end up freezing faster than an otherwise identical container that started out colder.

I know, infact I wrote some myself if you noticed.

I don't know, from personal experience, whether such conditions actually exist, but you are trying to apply thermodynamics in an inappropriately simplified form for the situation described.

No, it'e exactly the opposite: *they* are oversimplifying things. If one said: "under some specific circumstances a pot with hot water can freeze faster than another one with cool water" it would be *very different*. Instead, it's false science to say *hot water freezes faster than cool water*. I know that you don't appreciate all this difference, but there is. The first reason that comes to my mind is that people can be confused and brought to think that hot water freezes faster than cool one, in general and believe me, with especially with the help of internet, the risk is very high. The net has enormously amplified the exchange of informations, and at the same time has mixed the "pure" with the "impure".

I have some teaching experience and I continuously see people who should be cultured, for example journalists, say such stupid things that a child, 30 years ago, could have said: "what are you talking about? Are you crazy?" Who or what is responsible for this?

If you don't believe me, wait some other years and then you'll realize better. I talk with university students of technical faculties, that can tell you amazing things about what they studied, but ask them a simple question of physics, mathematics, chemistry on which they have to make a simple reasoning and you'll put them under embarassement. Some examples:
"if you put a piece of lead on water, will it float or will it go down?" No answer. "How much is it 10 percent of 100?" No answer. "What happens if you mix sodium carbonate with nitric acid? Does reactions happen? Which ones?" No answer.
I'm not kidding! I asked them personally such kinds of question; in my job I have to teach sometimes to new arrived. They know a lot of things, but they cannot put together the simpler ones. And I'm talking of tens of young people.
It can be a problem limited to here in Italy, don't know, I hope in UK it's different. The problem is they teach too much things at school that people becomes totally incapable to reason by its own.

If the water were at the same temperature throughout the container (top to bottom), it would be valid to assume that the container with the higher temperature must pass through a state with the same temperature as the cooler one started at, that this would take time, and that therefore the hotter sample must take longer to cool.
However, since water does -not- cool at a uniform temperature throughout its bulk, due to convection currents and to the fact that the rate at which heat is lost need not be constant in all directions (and in a freezer will certainly not be so).
No-one is claiming that hot water always freezes faster than cold water,

You *think* that no-one is claiming that, but people with poor knowledge and, mostly, poor ability to reason on its own is not able to understand that simple statement you have done.

[Geezer]

Ahem  [], if I might, if we try to address the original question, the answer is no. Thermodynamics still wins (and I think that's Lightarrow's point).

If we ask the question like this;

"Is it possible that under a certain set of very specific circumstances it appears that a mass of warmer water can freeze more quickly than the same mass of colder water?"

I think the answer is maybe. It's not obvious that a satisfactory experiment has been devised that proves the point one way or another.

If someone can take any arbitrary number of molecules of water at different temperatures and demonstrate that the warmer water always crystallizes first, I'll be a believer. Until them, I'm sticking with thermodynamics (and I'm not buying into the idea that we can use cold fusion as a source of energy either).   

[tommya300]

maybe this is possible Geezer?

Producing a miniature weather pattern:
Steamy energetic water, in  a container, producing water vapors, is placed in a freezer.
The surface of the water in the container is cooling as the vapors escape.
But not all water vapors are lost, some condense and circulate above in a cycle to attempt to gain a lattice crystal structure, precipitates, dropping to the surface and transfers the exchange of heat.
When the water surface reaches its highest density the lattice crystallization begins at the condensed vapor level  and begins to displace the warm water below it. As this happens water begins to freeze at the surface first.
It is the vapors of the hot water creating an additional heat sink.
Note it is slushy not solid ice.
The other room temperature water does not have the abundance of energetic water vapors to do this extra heat sink exchange. 

This is the most logical explanation that I have seen in regard to the phenomenon.  Have you performed experiments to substantiate your conclusions?  If so, I believe you should write it up and submit it for consideration.  This is not a new subject.  I remember reading about it many years ago.  Thanks for comments.  Joe L. Ogan

[Geezer]

maybe this is possible Geezer?

Producing a miniature weather pattern:
Steamy energetic water, in  a container, producing water vapors, is placed in a freezer.
The surface of the water in the container is cooling as the vapors escape.
But not all water vapors are lost, some condense and circulate above in a cycle to attempt to gain a lattice crystal structure, precipitates, dropping to the surface and transfers the exchange of heat.
When the water surface reaches its highest density the lattice crystallization begins at the condensed vapor level  and begins to displace the warm water below it. As this happens water begins to freeze at the surface first.
It is the vapors of the hot water creating an additional heat sink.
Note it is slushy not solid ice.
The other room temperature water does not have the abundance of energetic water vapors to do this extra heat sink exchange. 

I sort of see what you are saying Tommy. I'd like to see as few molecules of water as possible involved. I have no doubt that there are all kinds of interesting stratification and transfer effects going on when there is a large volume of water.

If we are going to say that warm water freezes faster than cold water, it would have to be true in all cases, even when there are only a few molecules of water involved.

The other thing I'd like to see is some accurate method of determining the actual thermal energy removal rate. Puting the whole thing into a freezer does not provide any data regarding the rate of energy transfer, which I think is very important, particulaly as we are changing the state of the water.

The energy transfer will consist of two components. The first simply cools the water to 0C, and the second removes the energy to allow the state change to occur. The second component is much greater than the first, particularly when we are starting off with water that's only a few degrees above freezing, so other small variables might be swamping the data associated with the first component.

[tommya300]

Since the question can be restated to represent a particular condition for each sampled model.
Freezing solid was not a condition.
Just to achive an ice crystal and to which system would show a sign to this affect.
Water vapor in abundance can be visually seen. Some supercooling must be occuring with the vapors.

Frost on the side of the container will develop and drop which will help the cooling process, speed things up with thermal sink or contact.
As soon as the surface of the water reaches 4 degrees C it is at its max density displacing an other density of water below it. What happens to the water above this thin layer?
I think the trick is is to prove the water at the surface is at 4 deg C without disturbing the medium.

When it came to freezing a cooked meal, I was told to bring it to room temperature before freezing, Why?
I was told to prevent early signs of freezer burn, frost developing on the food from the hot vapors.

I thought that hot water can cool quicker then cool water as it approaches the freezing point but  the cool water sample will freeze solid before the warmed water sample. At least that is what I can remember

[Geezer]

But if you can't determine a specific condition, it's imossible to run a meaningful experiment.

For example, when is a lake "frozen"?

When the first ice crystal appears, but how would you know?
Or is it when the entire lake is frozen solid - not sure when you'd know that either.
And, if we go back to the original observation, how would you know icecream is frozen?

Of course, as there is only a physical change involved, we could try running the experiment in the other direction.

If the observation is true, I'd expect that we'd observe some interesting non-linearity in temperature if we applied a constant amount of thermal energy to ice. (It's probably a lot simpler to run that experiment too.)

[JP]

I think this is a very good example of how models of a system work in physics.  Usually, if you're trying to model a system you start with the simplest possible model based on known physics.  Then, if the experiments match its predictions, you keep the model.  If experiments disagree with it, you start looking for ways in which you might have oversimplified things, and you introduce a more complex model (still base on known physics).  The problem I have is when people take the failure of their first model to mean that they've discovered some completely new physics.  I don't think that's where Joe was going with this question.

The problem here is that there is a simple and very intuitive model: cooling rate depends only on temperature of the water.  This model is apparently wrong, according to experiments.  If you think about it, it's not so hard to accept that it could be wrong.

Consider a simple example of two identical metal balls.  I heat the center of one up, while I heat up the surface of the second in a way that they both have the same average temperature.  Then I leave them to cool.  The one with the heated surface will cool faster, since all its heat is right at the surface where it can escape to the surrounding air easily.  In the second ball, the heat has to flow form the center outwards until it reaches the surface, then it can escape.  The problem is that you need to use heat transfer models here, not just an ideal-gas-law-type equation.  

Modeling the water is much more complicated since you probably need to account for convection currents, which depend on the temperature of the water, along with the different cooling rates on each surface of the water's container.   This isn't violating thermodynamics, but its a more realistic model than just assuming cooling rate depends on temperature alone.  It's also extremely hard to compute, which is why I think there isn't a satisfactory answer yet.  You also have to know the initial conditions of the water--I don't know if assuming an initially uniform temperature distribution, but a container with an open top is enough to cause this effect.  Maybe I'll try an experiment this weekend.   []

[JP]

By the way, the title of the post, "Will hot water freeze faster than cold waver?" is a bit misleading since it makes it sounds like it always happens.  The question Joe asks in the first post isn't misleading, since he asks if it's possible for it to happen.  Yes, it is possible, but no--it can't always happen.

[tommya300]

By the way, the title of the post, "Will hot water freeze faster than cold waver?" is a bit misleading since it makes it sounds like it always happens.  The question Joe asks in the first post isn't misleading, since he asks if it's possible for it to happen.  Yes, it is possible, but no--it can't always happen.

Will hot water ever freeze faster than cold water.  If it does, why does it freeze faster than cold water?  Thanks for comments.  Joe L. Ogan

JP isn't this his original post?

Where does he say, "if it's possible for it to happen"?

I see that different conditions affect the model! Promoting different results

[Geezer]

Ah, but we're not talking about cooling the water. The question was about freezing, but it's not very clear what was meant by that term.

If it means the entire mass of water becomes frozen, the discussion about localized effects may be less important. If it means when the first ice crystal forms then localized effects are more important.

If we are only interested in the rate of thermal energy transfer while the water is still liquid, it's quite simple to include an agitator in the water sample so that it has fairly uniform temperature. In fact, as we (hopefully) agree that pure water only starts to freeze at 0C (at STP), we can then leave out the freezing bit altogether, and focus on the energy that has to be removed to lower the temperature to 0C.

I'm reasonably confident that if we run that experiment we will observe that the amount of heat that has to be extracted is always consistent with the initial temperature of the sample.

If we want to get a bit more sophisticated, if our apparatus removes heat at a constant rate, we can even determine a "freezing point" when the water is starting to freeze. When that happens, the temperature of the sample will remain almost constant because of the very large amount of energy that has to be removed for water molecules to change state.

BTW, if we don't allow the water sample to be mixed/stirred/agitated, how do we even know what its temperature is?

[tommya300]

But if you can't determine a specific condition, it's imossible to run a meaningful experiment.

For example, when is a lake "frozen"?

When the first ice crystal appears, but how would you know?
Or is it when the entire lake is frozen solid - not sure when you'd know that either.
And, if we go back to the original observation, how would you know icecream is frozen?

Of course, as there is only a physical change involved, we could try running the experiment in the other direction.

If the observation is true, I'd expect that we'd observe some interesting non-linearity in temperature if we applied a constant amount of thermal energy to ice. (It's probably a lot simpler to run that experiment too.)

You can not observe the full surface of a lake that would take some doing.
Bit a cup of hot water in  a freezer can be observerd. I am sure you can see a small crust of ice forming in an open lid in the freezer.
Joe wanted to know why it happens.

[tommya300]

Ah, but we're not talking about cooling the water. The question was about freezing, but it's not very clear what was meant by that term.

If it means the entire mass of water becomes frozen, the discussion about localized effects may be less important. If it means when the first ice crystal forms then localized effects are more important.

If we are only interested in the rate of thermal energy transfer while the water is still liquid, it's quite simple to include an agitator in the water sample so that it has fairly uniform temperature. In fact, as we (hopefully) agree that pure water only starts to freeze at 0C (at STP), we can then leave out the freezing bit altogether, and focus on the energy that has to be removed to lower the temperature to 0C.

I'm reasonably confident that if we run that experiment we will observe that the amount of heat that has to be extracted is always consistent with the initial temperature of the sample.

If we want to get a bit more sophisticated, if our apparatus removes heat at a constant rate, we can even determine a "freezing point" when the water is starting to freeze. When that happens, the temperature of the sample will remain almost constant because of the very large amount of energy that has to be removed for water molecules to change state.

BTW, if we don't allow the water sample to be mixed/stirred/agitated, how do we even know what its temperature is?

You don't disturbing the model will affect the model, but can you agree that the hot water has more convection currents going on in the hot water and the vapors above the surface, then the cooler water sample. Can there be a vapor barrier between the water and the vapors in both system models?
Can the system having the more vapors condense and supercool more mass and drop into the water breaching the vapor barrier, in short time period?


Is it easier to prove ice will always start to melt at 0 deg C,  then it is to prove it will always freeze at 0 deg C?

[JP]

By the way, the title of the post, "Will hot water freeze faster than cold waver?" is a bit misleading since it makes it sounds like it always happens.  The question Joe asks in the first post isn't misleading, since he asks if it's possible for it to happen.  Yes, it is possible, but no--it can't always happen.

Will hot water ever freeze faster than cold water.  If it does, why does it freeze faster than cold water?  Thanks for comments.  Joe L. Ogan

JP isn't this his original post?

Where does he say, "if it's possible for it to happen"?

I see that different conditions affect the model! Promoting different results

Phrasing it as "will hot water ever freeze faster..." is asking if its possible that it ever happens.  It is.  The post title "will hot water freeze faster..." suggests a general rule, which isn't the case.  This is a problem where precisely stating the question is important.

[Geezer]

By the way, the title of the post, "Will hot water freeze faster than cold waver?" is a bit misleading since it makes it sounds like it always happens.  The question Joe asks in the first post isn't misleading, since he asks if it's possible for it to happen.  Yes, it is possible, but no--it can't always happen.

Will hot water ever freeze faster than cold water.  If it does, why does it freeze faster than cold water?  Thanks for comments.  Joe L. Ogan

JP isn't this his original post?

Where does he say, "if it's possible for it to happen"?

I see that different conditions affect the model! Promoting different results

Phrasing it as "will hot water ever freeze faster..." is asking if its possible that it ever happens.  It is.  The post title "will hot water freeze faster..." suggests a general rule, which isn't the case.  This is a problem where precisely stating the question is important.

Well, science says "never say never", so nothing can ever be ruled out. However, I've not seen anything that indicates there is even one reproducible experiment that confirms the effect even happens.

[JP]

Ah, but we're not talking about cooling the water. The question was about freezing, but it's not very clear what was meant by that term.

If it means the entire mass of water becomes frozen, the discussion about localized effects may be less important. If it means when the first ice crystal forms then localized effects are more important.

If we are only interested in the rate of thermal energy transfer while the water is still liquid, it's quite simple to include an agitator in the water sample so that it has fairly uniform temperature. In fact, as we (hopefully) agree that pure water only starts to freeze at 0C (at STP), we can then leave out the freezing bit altogether, and focus on the energy that has to be removed to lower the temperature to 0C.

Stirring would probably force the hot cup to always freeze first (neglecting a huge evaporation rate).  I interpreted the question as asking without stirring--just putting two cups of water in the freezer, which is easy to experiment on at home.

I'm reasonably confident that if we run that experiment we will observe that the amount of heat that has to be extracted is always consistent with the initial temperature of the sample.

Whether you stir or not (again neglecting evaporation) the heat removed to freeze the water completely is going to depend (almost) entirely on initial temperature.  (You might be able to make arguments about super cooling, though... which is where stirring might help.)  Since the hot cup has to lose more heat, the entire problem comes down to if it can have a faster heat loss rate throughout so that it can win the race, even though it has further to go.

BTW, if we don't allow the water sample to be mixed/stirred/agitated, how do we even know what its temperature is?

I think you could do it by heating water on a stove top up to a certain (uniform) temperature, then pouring it into the cup.  Temperature is an average kinetic energy, so you could theoretically just take the average over the whole cup once the hot water rises and the cold water sinks (doing that in reality is going to be difficult).  This points out why this isn't just temperature-dependent though, since once the cooling processes begin, its complicated to define a temperature if the water isn't uniform throughout.

There are two interesting points to this "Mpemba effect," assuming its as easy to repeat as the popular science write ups say...  The first is that hotter water can often somehow automatically "boost" its cooling rate when you put it in the freezer.  The second is that it shows how the scientific method works.  If the simple, intuitive model fails, you can either come up with a more complicated and accurate model, or you can do as Geezer suggests and try to account for the complications (by constantly stirring, for example).  

[JP]

Well, science says "never say never", so nothing can ever be ruled out. However, I've not seen anything that indicates there is even one reproducible experiment that confirms the effect even happens.

You can find a bunch of experiments here: http://scholar.google.com.sg/scholar?hl=en&q=Mpemba+effect [Links inactive - To make links active and clickable, login or click here to register]

Some peer-reviewed papers on the subject:
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000063000010000882000001&idtype=cvips&gifs=yes&ref=no [Links inactive - To make links active and clickable, login or click here to register]

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000074000006000514000001&idtype=cvips&gifs=yes&ref=no [Links inactive - To make links active and clickable, login or click here to register]

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000077000001000027000001&idtype=cvips&gifs=yes&ref=no [Links inactive - To make links active and clickable, login or click here to register]

This site also has a bibliography on it: http://www1.lsbu.ac.uk/water/explan.html#mpemba [Links inactive - To make links active and clickable, login or click here to register]

[tommya300]

"Sublimation, Evaporation, and Condensation
The surface of solid ice or liquid water is a busy place. Water molecules are constantly
leaving it as water vapor and returning to it as ice or water. When molecules
leave the surface, the water is evaporating or the ice is subliming. When molecules
return to the surface, the water vapor is condensing. This simple picture of
water molecules taking off and landing on the surface of ice or water explains
many familiar phenomena. But to complete the picture, we must follow the flow
of energy in this system.
Ice and water both contain thermal energy, which is exchanged between
neighboring molecules and keeps them in motion. While the average water molecule
is unable to break free from the surface, molecules occasionally obtain
enough thermal energy from their neighbors to break their bonds and leave as
water vapor. In doing so, these molecules carry away more than their fair share
of the water or ice’s thermal energy and it becomes colder. Your body uses this
effect to keep cool on hot summer days, when perspiration that evaporates from
your skin draws heat from you and lowers your temperature."

http://www.howeverythingworks.org/supplements/water_steam_and_ice.pdf [Links inactive - To make links active and clickable, login or click here to register]
------------------------------------------------------
http://www1.lsbu.ac.uk/water/explan.html#mpemba [Links inactive - To make links active and clickable, login or click here to register]

Initially-cold water freezes at a lower temperature to a more completely solid ice with less included liquid water; the lower temperature causing intensive nucleation and a faster crystal growth rate. If the freezing temperature is kept about -6°C then the initially-hot water is most likely to (apparently) freeze first. If freezing is continued, initially-cold water always completely freezes before initially-hot water.

I see that graph and the temperature decay vs time

Still revising the ideas of the reasons why...from 2006 to 2009, someone will have the final answer applying some new tech measuring tool.

[Geezer]

"A number of scientists have investigated Mpemba's claim, but their results remain inconclusive."

http://physicsworld.com/cws/article/print/24493 [Links inactive - To make links active and clickable, login or click here to register]

This might be one for Snopes. It seems to have become part of scientific (as opposed to urban) mythology. Personally, I blame Aristotle.

Is there at least one repeatable experiment?

[Geezer]

Sorry for the second post, but I didn't think an edit was appropriate.

Let's get back to basics. Before we try to explain a phenomenon, would it not be a good idea to describe what the phenomenon actually is?

I would think that if it is not possible to reproduce a phenomenon consistently, we really don't know what we are investigating. Just because a bunch of people seem to believe that something happens is no reason to believe that something actually does happen.

So, if this is such a well accepted phenomenon, you'd think there would be a well accepted experiment that demonstrates the phenomenon. That being the case, you'd think it would be rather well documented by now.

The Geezer view is that a lot of scientists have had a lot of smoke blown up their kilts. Cold Fusion was debunked because the stakes were so high. I'm not sure this one would have survived an equal amount of scrutiny.

[tommya300]

"A number of scientists have investigated Mpemba's claim, but their results remain inconclusive."

http://physicsworld.com/cws/article/print/24493 [Links inactive - To make links active and clickable, login or click here to register]

This might be one for Snopes. It seems to have become part of scientific (as opposed to urban) mythology. Personally, I blame Aristotle.

Is there at least one repeatable experiment?

Yea Ice melts at 32 degrees F, always

[tommya300]

Sorry for the second post, but I didn't think an edit was appropriate.

Let's get back to basics. Before we try to explain a phenomenon, would it not be a good idea to describe what the phenomenon actually is?

I would think that if it is not possible to reproduce a phenomenon consistently, we really don't know what we are investigating. Just because a bunch of people seem to believe that something happens is no reason to believe that something actually does happen.

So, if this is such a well accepted phenomenon, you'd think there would be a well accepted experiment that demonstrates the phenomenon. That being the case, you'd think it would be rather well documented by now.

The Geezer view is that a lot of scientists have had a lot of smoke blown up their kilts. Cold Fusion was debunked because the stakes were so high. I'm not sure this one would have survived an equal amount of scrutiny.

Yea I was reading weather and evaporations on a large scale and reducing it in scale.
I gain some knowledge here thank you for the patience too.

[JP]

"A number of scientists have investigated Mpemba's claim, but their results remain inconclusive."

http://physicsworld.com/cws/article/print/24493 [Links inactive - To make links active and clickable, login or click here to register]

This might be one for Snopes. It seems to have become part of scientific (as opposed to urban) mythology. Personally, I blame Aristotle.

Is there at least one repeatable experiment?

There are a bunch of experiments summarized in this article: http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000074000006000514000001&idtype=cvips&gifs=yes&ref=no [Links inactive - To make links active and clickable, login or click here to register]

If you can't get to that, the one with the most repeatability seems to be the one by Jearl Walker in the article you cite.   To be fair, "although Walker
reported that he could reproduce most of his results, he still obtained large deviations in some of them."

I'm not sure that comparing this to cold fusion is fair, since cold fusion had/has a lot more funding and it was only claimed once to my knowledge (and then debunked.)  This effect has no where near that level of funding and has claims of observations in several different experiments.   

I strongly suspect this is reproducible, though it certainly doesn't overturn thermodynamics, but that it's not worth the time and effort required to do a systematic study that controls for all the variables.  This one is essentially in the realm of enthusiasts and high school science fair projects rather than high-tech labs.