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

  1. Oct 26, 2015 #1
    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 ???
  2. jcsd
  3. Oct 26, 2015 #2
    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.
  4. Oct 26, 2015 #3


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    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.
  5. Oct 26, 2015 #4
    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.
  6. Oct 26, 2015 #5
    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:

  7. Oct 26, 2015 #6


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    What happens when the initially hot water reaches the initial temperature of the cold water?
  8. Oct 26, 2015 #7
    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]>
    Last edited by a moderator: May 7, 2017
  9. Oct 26, 2015 #8


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    Here's the thread where I posted the results of the experiment I did, showing no effect: https://www.physicsforums.com/threa...-tray-freeze-quicker-than-one-at-33-f.205920/

    Nor have I. In particular, results from a junior high science fair project from 50 years ago are less than persuasive. That has all of the hallmarks of a myth.
  10. Oct 26, 2015 #9
    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.
  11. Oct 26, 2015 #10
    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!
  12. Oct 26, 2015 #11


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    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:
    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.
  13. Oct 26, 2015 #12
    But once it cools this will stop happening.
  14. Oct 26, 2015 #13
    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:
    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.
  15. Oct 26, 2015 #14
    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?
  16. Oct 26, 2015 #15


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    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.
  17. Oct 26, 2015 #16
    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.

  18. Oct 26, 2015 #17
  19. Oct 26, 2015 #18

    Andy Resnick

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    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.
  20. Oct 26, 2015 #19
  21. Oct 26, 2015 #20


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    You mean like here?

  22. Oct 27, 2015 #21
    Then why someone says that hot water can freeze faster than cold water?:

  23. Oct 27, 2015 #22
    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]
    Last edited by a moderator: May 7, 2017
  24. Oct 27, 2015 #23


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    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.
    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.
    Last edited by a moderator: May 7, 2017
  25. Oct 27, 2015 #24
    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!
    Last edited by a moderator: May 7, 2017
  26. Oct 27, 2015 #25
    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.
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