# How can boiling water freeze faster than water at room temp?

• feyn

#### feyn

Hi guys n girls,

I have a real conundrum today. There us a rumor that if you put 2 pots of water, that are absolutely identical except that in one the water is boiling hot in the other it is room temperature, the one with the boiling water freezes faster. How can that be ?

Pure logic dictates that at some point the boiling water reaches room temperature as well, and should need then just as long as the one that started at that temperature from that moment on, plus the time it needed to reach that point, so clearly longer. What is gouing on here ?

## Answers and Replies

I've never seen convincing experimental evidence to support this claim.

But if the experiment is not careful, starting with equal masses of boiling and room temperature water, greater evaporation of the boiling water could leave a lower mass of the ice that began as boiling water.

It is also possible that if convection is an important cooling mechanism in the boiling water, favorable convection currents could lead to more rapid cooling in the boiling water than in the room temperature water. It is easier to keep a convection current going once it is started than to originate a convection current.

You are correct: except under highly specific and unusual circumstances, the cold water will freeze first. Do a search of the forum; several years ago I did an experiment and posted the results.

The reason that I believe is that because the boiling water has a much greater difference in temperature, the heat of the boiling water is distributed much faster than the one at room temperature, so the one with its heat being extracted faster should reach its freezing point quicker. I may be wrong, I haven't done this experiment in years.

It is called the Mpemba effect (although it was already described by aristotle) and it is still unclear what causes it. The most recent research suggests it is due to a combination of convection and supercooling:

https://en.wikipedia.org/wiki/Mpemba_effect

_Anthony_
The reason that I believe is that because the boiling water has a much greater difference in temperature, the heat of the boiling water is distributed much faster than the one at room temperature, so the one with its heat being extracted faster should reach its freezing point quicker.
What happens when the initially hot water reaches the initial temperature of the cold water?

M Saad, _Anthony_ and nasu
the following info drawn from wikipedia may provide a field for further input- no doubt there can be other explanations but the effect seems to be real;

<https://en.wikipedia.org/wiki/Mpemba_effect> [Broken]

<The effect is named after Tanzanian Erasto Mpemba. He described in 1963 in Form 3 of Magamba Secondary School, Tanganyika, when freezing ice cream mix that was hot in cookery classes and noticing that it froze before the cold mix.

He later became a student at Mkwawa Secondary (formerly High) School in Iringa. The headmaster invited Dr. Denis G. Osborne from the University College in Dar Es Salaam to give a lecture on physics.

After the lecture, Erasto Mpemba asked him the question "If you take two similar containers with equal volumes of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and put them into a freezer, the one that started at 100 °C (212 °F) freezes first. Why?",

only to be ridiculed by his classmates and teacher. After initial consternation, Osborne experimented on the issue back at his workplace and confirmed Mpemba's finding.
They published the results together in 1969, while Mpemba was studying at the College of African Wildlife Management.[8]

A reviewer for Physics World writes, "Even if the Mpemba effect is real — if hot water can sometimes freeze more quickly than cold — it is not clear whether the explanation would be trivial or illuminating." He pointed out that investigations of the phenomenon need to control a large number of initial parameters (including type and initial temperature of the water, dissolved gas and other impurities, and size, shape and material of the container, and temperature of the refrigerator) and need to settle on a particular method of establishing the time of freezing, all of which might affect the presence or absence of the Mpemba effect. The required vast multidimensional array of experiments might explain why the effect is not yet understood.[1]

New Scientist recommends starting the experiment with containers at 35 °C (95 °F) and 5 °C (41 °F) to maximize the effect.[16]

In a related study, it was found that freezer temperature also affects the probability of observing the Mpemba phenomena as well as container temperature. For a liquid bath freezer, a temperature range of −3 °C (27 °F) to −8 °C (18 °F) was recommended.[14]

In 2012, the Royal Society of Chemistry held a competition calling for papers offering explanations to the Mpemba effect.[17] More than 22,000 people entered and Erasto Mpemba himself announced Nikola Bregović as the winner, suggesting that convection and supercooling were the reasons for the effect.[18]>

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_Anthony_
The latest info from Phys.org:
A team of physicists at the Nanyang Technological University in Singapore have now published what they believe may be the solution.
They claim that the explanation lies in the unusual interaction between the molecules of water.

Each water molecule is bound to its neighbour through a highly charged electromagnetic bond known as a “hydrogen bond”.

It is this that produces surface tension in water and also gives it a higher than expected boiling point compared to other liquids.

However, Dr Sun Changqing and Dr Xi Zhang from Nanyang Technological University, argue this also determines the way water molecules store and release energy.

They argue that the rate at which energy is released varies with the initial state of the water and so calculate that hot water is able to release energy faster when it is placed into a freezer.

Dr Changqing said: “The processes and the rate of energy release from water vary intrinsically with the initial energy state of the sources.”

some others point out that-
They say the interaction between the hydrogen bonds and the stronger bonds that hold the hydrogen and oxygen atoms in each molecule together, known as covalent bonds, is what causes the effect.

Normally when a liquid is heated, the covalent bonds between atoms stretch and store energy.

The scientists argue that in water, the hydrogen bonds produce an unusual effect that causes the covalent bonds to shorten and store energy when heated.

This they say leads to the bonds to release their energy in an exponential way compared to the initial amount stored when they are cooled in a freezer.

well those researchers who did not get the effect in their expts. should also publish to counter the claims by the other groups-this is science!

...well those researchers who did not get the effect in their expts. should also publish to counter the claims by the other groups-this is science!
This supposed effect gets a big yawn from scientists because water is already so well understood that there is very little room for this effect to be possible except in rare, highly specific/contrived circumstances. Water/ice/steam is used as the working fluid in steam engines and air conditioning systems. You can google for a table that provides its properties at different temperatures. None of those tables include any sort of caveat that those properties depend on the route you took to get the water to that state. IE:
However, Dr Sun Changqing and Dr Xi Zhang from Nanyang Technological University, argue this also determines the way water molecules store and release energy.

They argue that the rate at which energy is released varies with the initial state of the water and so calculate that hot water is able to release energy faster when it is placed into a freezer.

Dr Changqing said: “The processes and the rate of energy release from water vary intrinsically with the initial energy state of the sources.”
That is contrary to the observed behavior of water. It simply isn't possible.

While we have generally humored threads about this subject, the nature as a likely urban myth invites pseudoscience, but please bear in mind that this is a science forum and we require discussions to be scientific and ideas contrary to established science must at least be peer reviewed and published. Please provide the source of what you just posted.

The reason that I believe is that because the boiling water has a much greater difference in temperature, the heat of the boiling water is distributed much faster than the one at room temperature, so the one with its heat being extracted faster should reach its freezing point quicker. I may be wrong, I haven't done this experiment in years.
But once it cools this will stop happening.

I remember reading a paper from Zhang a while ago. Here is a link to one of his papers showing measurements and a model that reproduces the effects:
http://pubs.rsc.org/en/content/articlepdf/2014/cp/c4cp03669g
I have no idea what the quality is of this journal, if it is peer-reviewed or not. I find the comparison between measurements and simulations quite convincing, but the ideas behind supersolidity and hydrogen bonding is still quite weak theoretically in my opinion. There is no real reference to other scientific publications explaining this model.

I don't get this at all.
If the two containers are identical other than in temperature, then the hotter one will cool until it eventually reaches the original temperature of the colder one.
At this point it is in an identical condition to that in which the colder container originally was.
Why then should it behave any differently to the other container when cooled further after that point?

Slartibardfast, M Saad, _Anthony_ and 1 other person
I don't get this at all.
If the two containers are identical other than in temperature, then the hotter one will cool until it eventually reaches the original temperature of the colder one.
At this point it is in an identical condition to that in which the colder container originally was.
Why then should it behave any differently to the other container when cooled further after that point?
That was my point of my post #6. The only other possibility is that there is a memory effect, which is what the Zhang paper cited in post #13 claims. I didn't yet have time to read it, but my guess is that they found a solution to a non-existing problem.

Thank you everyone for the links and documentation. I thought this was an urban myth and put it out of my mind after I watched the Mythbusters episode. Now that I know it is science, just not science most people know, including scientists, I'm going to experiment.

Anthony

https://www3.ntu.edu.sg/home/ecqsun/CCR-H2O.pdf
http://www3.ntu.edu.sg/home/ecqsun/RTF/JPCL-Water%20Densty.pdf

Hi guys n girls,

I have a real conundrum today. There us a rumor that if you put 2 pots of water, that are absolutely identical except that in one the water is boiling hot in the other it is room temperature, the one with the boiling water freezes faster. How can that be ?

Pure logic dictates that at some point the boiling water reaches room temperature as well, and should need then just as long as the one that started at that temperature from that moment on, plus the time it needed to reach that point, so clearly longer. What is gouing on here ?

The consideration that has been missing form this thread is the surface area/volume ratio, because while the total heat is proportional to the volume, the rate of heat transfer is proportional to the surface area. This is why, on a very cold day, tossing a pot full of hot water into the air will result in snow while doing the same with a pot of cold water will not- the spray creates an enormous surface area, and so the heat loss is faster than the corresponding change in temperature.

As for putting identical pots of water into the freezer, I expect the results will vary with initial volume, for the same reason.

M Saad and Nemika
except under highly specific and unusual circumstances

You mean like here?

I don't get this at all.
If the two containers are identical other than in temperature, then the hotter one will cool until it eventually reaches the original temperature of the colder one.
At this point it is in an identical condition to that in which the colder container originally was.
Why then should it behave any differently to the other container when cooled further after that point?
Exactly.
Then why someone says that hot water can freeze faster than cold water?:
http://math.ucr.edu/home/baez/physics/General/hot_water.html

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lightarrow

M Saad
The key idea is that hydrogen bonds bring water molecules into close contact and when this happens the natural repulsion between the molecules causes the covalent O-H bonds to stretch and store energy.

But as the liquid warms up, it forces the hydrogen bonds to stretch and the water molecules sit further apart. This allows the covalent molecules to shrink again and give up their energy. The important point is that this process in which the covalent bonds give up energy is equivalent to cooling.

In fact, the above effect is additional to the conventional process of cooling. So warm water ought to cool faster than cold water

some guys have calculated the magnitude of the additional cooling effect and show that it exactly accounts for the observed differences in experiments that measure the different cooling rates of hot and cold water.
reference;https://physics-arxiv-blog/why-hot-water-freezes-faster-than-cold-physicists-solve-the-mpemba-effect [Broken]

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So warm water ought to cool faster than cold water
Warm water does cool faster than cold water (because the cooling rate is proportional to temperature difference) -- and then it becomes cold water and cools at the same rate as other cold water.
https://physics-arxiv-blog/why-hot-water-freezes-faster-than-cold-physicists-solve-the-mpemba-effect [Broken]
Link doesn't work. Please post a functional link.

One thing I've noticed in these links posted is that while they build mathematical models, I've never seen an experiment performed to demonstrate the phenomena actually exists in the way described.

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M Saad and nasu
russ_watters,
well i could not get the arxiv -blog on google again- sorry for that but a detail work has come up and you can see the experimental details in the following ref.
https://www.binghamton.edu/physics/docs/Preprint%20and%20Supplemental%209%20Mar%2010.pdf> [Broken]
sorry for the inconvenience;
my point is that thermal exchanges and Newton's law of cooling works but if a paradox emerges ,the catch must be somewhere else!

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DrClaude
But once it cools this will stop happening.
I've said this in a previous thread, explain why. It does no help to just state something without providing an explanation to the statement. By explaining your statement we can get to the answer of this thread quicker and more efficiently.

I've said this in a previous thread, explain why. It does no help to just state something without providing an explanation to the statement. By explaining your statement we can get to the answer of this thread quicker and more efficiently.
Newton's law of cooling is based on the observed fact that heat flow is proportional to temperature difference. So if you start off with twice the temperature difference you get twice the heat flow. When the temperature of the "hot" water reaches the starting temperature of the "cold" water, it must continue following that law and follow exactly the same temperature profile that the "cold"water followed.

my point is that thermal exchanges and Newton's law of cooling works but if a paradox emerges ,the catch must be somewhere else!
Indeed that's true: but my point is that I've never seen convincing evidence that the paradox actually exists. All of these papers build mathematical models to attempt to explain something that hasn't been shown to be real and violates established science. That's putting the cart miles before the horse!

Indeed that's true: but my point is that I've never seen convincing evidence that the paradox actually exists. All of these papers build mathematical models to attempt to explain something that hasn't been shown to be real and violates established science. That's putting the cart miles before the horse!
I agree, there is indeed no paradox, but the Mpemba effect is real nonetheless. Have you read the Brownridge paper referred to above? I think it addresses most issues we are discussing. He performed detailed measurements (in an actual lab) and he could create setups where the Mpemba effect never occurs and setups where it always occurs.

One issue is that 'everything else equal' (which is by the way not a requirement in the description of the Mpemba effect) means that the initial conditions of the experiment are exactly the same, except for the temperature. Of course, by the time the hot water has reached the initial temperature of the cold water, there must be a difference, in the boundary conditions or elsewhere, between the hot water setup and the cold water setup.
Another issue is that the point of freezing is usually not 0 degrees Celcius. When T1 < T2 and the boundary conditions stay the same, then the water at T1 will always cool to 0 C in a shorter time than the water at T2. But water will not always freeze at 0 Celcius, and supercooling is actually quite common. This supercooling is affected by nucleation sites present in the water and boiling the water affects the number of nucleation sites.

Issue 1: Brownridge presents a setup where you put the water in a copper container and then place it on the frost layer in the freezer. The cup of hot water will immediately melt the frost below the cup, which will then refreeze as ice. Of course, by the time that the hot water reaches the initial temperature of the cold water, the boundary conditions are completely different (thermal conductivity of the ice layer below the container is higher than the thermal conductivity of the frost layer).

Issue 2: Brownridge spends a lot of time on the supercooling effect and his conclusion is:
"The Mpemba effect, describing the phenomenon of initially hot water freezing before cooler water, occurs only when the water supercools and the cooler water has a lower nucleation temperature than the warmer water"
"[] when liquid water is cooled from above 0 oC, it often will not begin freezing until it has supercooled to several degrees below 0 oC. This is why hot water can freeze before cooler water when all experimental conditions are identical except for the initial temperatures of the water. Hot water will freeze before cooler water only when the cooler water supercools, and then, only if the nucleation temperature of the cooler water is several degrees lower than that of the hot water. Heating water may lower, raise or not change the spontaneous freezing temperature."

The Brownridge paper shows that there is no need for exotic theories about OH bonds. You either have different (time-dependent) boundary conditions in the hot and cold experiment, or your water is actually different (different number of nucleation sites).

DrClaude
I agree, there is indeed no paradox, but the Mpemba effect is real nonetheless. Have you read the Brownridge paper referred to above? I think it addresses most issues we are discussing. He performed detailed measurements (in an actual lab) and he could create setups where the Mpemba effect never occurs and setups where it always occurs.
I hadn't been able to access it until now. Here's the corrected link (and I fixed it in its original post as well):
https://www.binghamton.edu/physics/docs/Preprint%20and%20Supplemental%209%20Mar%2010.pdf

I'm only 7 pages into it, but so far it is an excellent article. It says what I and others have been saying: if all other conditions but starting temperature are controlled to, there is no effect, but the effect can be generated by introducing certain inequalities. The first one (non-control) is where two copper cups are placed on a bed of freezer frost. The warm one melts the frost, creating a vastly improved heat transfer interface and much faster cooling.
One issue is that 'everything else equal' (which is by the way not a requirement in the description of the Mpemba effect...
Disagree. If "everything else is equal" is not at least implied, then there is no mystery/paradox to resolve. I could easily just say "hot water freezes faster than cold water if I put the hot water in the freezer and drink the cold water." That's not just unsurprising and not a paradox, it's just plain stupid. To put a finer point on it, the OP says "identical" and the wiki on the subject in different descriptions uses "identical" and "similar" and in folk tales if a difference were known one would do better to directly exploit the actual difference rather than indirectly exploit it by using hot water.
Of course, by the time the hot water has reached the initial temperature of the cold water, there must be a difference, in the boundary conditions or elsewhere, between the hot water setup and the cold water setup.
That isn't true. In the first experiment in the article, he sealed the water in a glass vial and repeated the experiment dozens of times (both with tap water and de-ionized water) in order to make all other conditions besides starting temperature exactly identical. As should be expected, the effect did not manifest.

This subject actually irritates me a little because the typical flatly stated urban myth description can lead people to wrong understanding and/or wrong actions if someone believes it at face value. Wiki credited Aristotle (oh, how I despise Aristotle) with popularizing the general practice of leaving water in the sun before trying to freeze it (where did they put it to freeze it?), which is the wrong thing to do. I can see people now blithely putting hot water in their ice trays because they need a lot of ice for a party and think that will make it freeze faster!

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if all other conditions but starting temperature are controlled to, there is no effect,
What about the experiment in post #20. Would that work with room twater too?

What about the experiment in post #20. Would that work with room twater too?
I don't know - it wasn't demonstrated. But while it may be similar if you are correct in your prediction, it strains the description of the effect and doesn't lend itself well to quantitative measurement of what is happening.

Surely someone has observed two equal containers, with equal amounts of water and at EQUAL temperature, one freezing faster than the other. Not every time, mind you, but under just the right conditions. Sounds a bit like the Mpemba effect. Maybe the higher temperature is a distraction, maybe something is happening at the quantum or a much larger level that effects freeze times.

Surely someone has observed two equal containers, with equal amounts of water and at EQUAL temperature, one freezing faster than the other. Not every time, mind you, but under just the right conditions. Sounds a bit like the Mpemba effect. Maybe the higher temperature is a distraction, maybe something is happening at the quantum or a much larger level that effects freeze times.
What happens is that when people says "hot water can freeze faster than cold water" they forget that, in a *scientific* experiment and not in home made one, "water" means "pure water" and not "water that can have air, gases, particles, salts inside/dissolved" and that in a scientific experiment the conditions must be controlled, equal for the two comparisons and the envinronment must be suitable for a freezing comparison (so it's not acceptable to make the experiment with environmental air temperature below 0°C as in experiment shown in #R20, for example, because in the case of hot water, the faster vaporization and then condensation subtracts amount of substance faster; it's as if you would manually take away water from one container, it's not acceptable).

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lightarrow

Newton's law of cooling is based on the observed fact that heat flow is proportional to temperature difference. So if you start off with twice the temperature difference you get twice the heat flow. When the temperature of the "hot" water reaches the starting temperature of the "cold" water, it must continue following that law and follow exactly the same temperature profile that the "cold"water followed.
Thank you for explaining your statement. But, if you can, on a night when the temperature is below freezing, can you take a pot of boiling water and throw it outside? I've done this experiment. If I remember correctly, when you do the experiment, the water should turn into snow or graupel(which is a form of precipitation between hail, sleet, rain, and snow). I know it's not the same as what the question is exactly asking, but it might be cool to do with both normal water and distilled water(or pure water, distilled is close to it and easier to find) to see if their is a noticeable difference.

Disagree. If "everything else is equal" is not at least implied, then there is no mystery/paradox to resolve. I could easily just say "hot water freezes faster than cold water if I put the hot water in the freezer and drink the cold water." That's not just unsurprising and not a paradox, it's just plain stupid. To put a finer point on it, the OP says "identical" and the wiki on the subject in different descriptions uses "identical" and "similar" and in folk tales if a difference were known one would do better to directly exploit the actual difference rather than indirectly exploit it by using hot water.
I was thinking about the following: if you boil water for a while, the freezing temperature of the water will change, so the initial composition of the water is different. Is this violating the conditions of 'all else equal'? The two water samples were the same before you started boiling one sample.
Actually, if boiling the water would add nucleation agents to the water, then the freezing temperature would be higher than the non-boiled water and the Mpemba effect could be due to this. But the opposite (less nucleation agents when you boil the water) is happening as shown in the paper, so boiling for a long period of time and cooling a sample of this water should even increase the time of freezing compared to a sample that was not boiled!

That isn't true. In the first experiment in the article, he sealed the water in a glass vial and repeated the experiment dozens of times (both with tap water and de-ionized water) in order to make all other conditions besides starting temperature exactly identical. As should be expected, the effect did not manifest.
Yes. My point was that something (a boundary condition, the composition of the water, the convection current in the water) must be different (at the moment that the hot water reaches the temperature of the cold water) or else the effect cannot occur. I think that the experiment with the copper containers in Brownbridge fulfills the requirement 'all else equal at the start of the measurement'.

The convection currents in the water might also play a dominant role under certain circumstances, but I haven't seen many studies on this, only this one on the royal society of chemistry website:
http://www.rsc.org/images/adam-smith-paper-entry_tcm18-225152.pdf [Broken]
According to these measurements, if your initial temperature is around 5 C then no convection currents will be formed. When you start with a higher temperature (20,40,60,80,100), the convection currents will result in a stronger cooling rate. There is then a trade-off between the time it takes to cool down from the initial temperature and the increase in cooling rate that you will (eventually) get. Also, the exact moment that the water starts to freeze is a statistical event and they show quite some spread in their measurements for the 5 C samples.

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