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Will a snowflake keep if you freeze it?

  1. Jul 8, 2013 #1
    If you were to somehow catch a snowflake and put it in a freezer before it melts, will it keep its shape? My gut says no. Thermal motion will make it slowly jiggle into a blob of ice, or it might fall apart under its own weight. Is my gut right? Unfortunately I don't live in a place where it snows so I have little relevant experience.
     
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  3. Jul 8, 2013 #2

    LeonhardEuler

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    Since a freezer takes in hotter air with a higher level of humidity than can remain at very low temperatures, more ice will tend to condense on the snowflake and it will lose its original shape fairly soon.
     
  4. Jul 8, 2013 #3

    A.T.

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    Since the structures form in free fall, I'm not sure if all of them can support their own weight, lying around somewhere.
     
  5. Jul 8, 2013 #4

    Drakkith

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    Why would you expect this? My desk has been around for 30+ years and is still its original shape. Ice is a solid and retains its shape unless something else causes it to change.

    Also, for those who don't think it can retain its shape under its own weight, I can see images of them doing just that on google images.
     
  6. Jul 8, 2013 #5

    sophiecentaur

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    An ice crystal would stay the same if it were kept in dry air, I imagine.
    Tupperware?
     
  7. Jul 8, 2013 #6
    I'm not so sure. Water will sublime straight from a solid to a vapor and freeze straight from a vapor to a solid. The net effect of these 2 processes will be to shuffle material around so I'm pretty sure the snowflake will loose it's shape. What I'm not sure of is the time-scale.

    Question for the O.P. What kind of time-scale were you asking about? Hours, months, years?
     
  8. Jul 8, 2013 #7
    Thanks for the quick replies :)

    I'm talking about a long time scale. I can imagine it still looking like a snowflake after a few minutes or even an hour, but what about after a week?

    I hadn't even thought about sublimation. That seems to make the answer certain. The snowflake will lose its shape without having to melt. Also LE's point about the humidity is a good one and gives the same result.

    What I'm driving at is, are snowflake patterns the result of an equilibrium process? The freezing of water into ice is. If you keep a block of ice below freezing in a closed container, it will stay ice forever. But even in a crystal, don't atoms rearrange themselves very occasionally? If you sealed off a desk in a very cold room for several eons, would it still look like a desk? My guess is no, but it would still be solid.

    I'm thinking that a snowflake is always either growing or dying. The large scale structure is qualitatively different from the microscopic crystal structure, which is stable.
     
  9. Jul 8, 2013 #8
    You already know that the shapes of snowflakes are not stable. Otherwise, they would all be the same shape.
     
  10. Jul 9, 2013 #9

    Drakkith

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    Yes, it would.

    Here is a link to a fossilized insect dated at 16-20 million years old: http://en.wikipedia.org/wiki/File:Leptofoenus_pittfieldae_(male)_rotated.JPG

    A tiny insect formed of fragile materials has been preserved for almost 20 million years. But that's nothing. The oldest fossils in existence are stromalites. Some have been dated to be over 3 BILLION years old and they've still kept their shape.

    If your desk was protected from corrosion and decay it would keep its shape effectively forever. Or at least until the Sun enters its red giant phase and engulfs the Earth.
     
  11. Jul 9, 2013 #10

    D H

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    This is the correct answer.

    Look what happens to ice cubes left in the freezer for too long. They shrink and eventually get spongy due to sublimation. The now porous ice cube will adsorb all kinds of odors lingering in the freezer.

    That's what happens with a solid ice cube. The surface area per unit mass of a snowflake is many orders of magnitude larger for a snowflake than for an ice cube. The couple of months or so that it takes for an ice cube to get to that stinky old ice cube state will happen in no time flat for a snowflake.
     
  12. Jul 9, 2013 #11

    LeonhardEuler

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    True, but I think it's important to keep in mind the differences between a desk and a snow flake. For the sake of simplicity, assume the desk is made of iron, but there is no oxygen so it doesn't rust.

    Looking around I find the vapor pressure of water to be 600 Pa at 0 Celsius and the vapor pressure of iron to be something like 10^(-59) Pa at the same temperature assuming I didn't mess up the calculation (formula here: http://en.wikipedia.org/wiki/Vapor_pressures_of_the_elements_(data_page [Broken]))

    So the chances of a water molecule evaporating off a snow flake over a given period of time are much, much higher than an iron atom evaporating off of the desk. The time scale for what mrspeedybob and DH are talking about is far, far faster for ice than most solids. You hear about the humidity levels, but never about the amount of iron vapor in the air, because the evaporation of an iron atom is a rare event.

    To answer techmologist's question, the formation of a snow flake is a dynamic process, and how big it grows depends on how long it spends in the air. Under the conditions in the atmosphere where snow flakes grow, equilibrium favors the formation of more solid over vapor, but the particular shape a flake takes depends on its history and is not necessarily the thermodynically most favored for a given set of conditions.
     
    Last edited by a moderator: May 6, 2017
  13. Jul 9, 2013 #12
    Chestermiller: that is another good point.

    Drakkith: You are right. It would take much, much longer than what I said for the desk to become a heap of whatever material it was made out of. Probably longer than the universe has been around. So practically forever. But I still say that, in principle at least, even crystals flow a little bit. An iron hammer out in deep space would eventually turn into an iron sphere if the universe lasted long enough. Thanks for the link to that wasp picture.

    D H: thanks for that good explanation of how ice cubes become stinky.

    So it seems to be established that intricate structure that makes a snowflake a snowflake forms spontaneously, but not as the equilibrium endpoint of some process. So it is different from the crystal structure of ice itself, or the spontaneous separation of oil droplets from oil mixed in water.
     
  14. Jul 9, 2013 #13
    Ah, thanks for that detailed explanation. Does a solid have to sublime in order to rearrange its atoms (while maintaining the same crystal structure, of course)? Can't the atoms just sort of move over each other, like a slow motion version of liquid flow? Or maybe that is an example of sublimation.

    I was looking at one of those websites that argues that order or structure or organization doesn't spontaneously arise in nature (it apparently contradicts the spirit of the 2nd Law, if not the letter) without the intervention of an intelligent agent. The only exceptions they allow to this rule are the somewhat humdrum structures resulting from equilibrium, such as the freezing of water into ice. But they lumped snowflakes in with these equilibrium structures. I thought that seemed out of place. Kinda nice of them to provide a beautiful counterexample to the claim they were making.
     
    Last edited by a moderator: May 6, 2017
  15. Jul 9, 2013 #14

    LeonhardEuler

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    Yes, atoms in a crystal can occasionally move past each other, but that is an extremely slow process, and it does not directly lead to a change in the overall macroscopic shape of an object. But in very old rocks the results of diffusion can be seen.

    The second law of thermodynamics doesn't have a spirit. Either something violates it or it doesn't. Structure and organization do spontaneously arise in nature. The bulk shapes of objects are not really subject to equilibrium because there are a small enough number of degrees of freedom there that unlikely shapes can very well arise simply by chance.

    At the microscopic level each atom has three degrees of freedom in position and three more degrees in momentum before you get to an even finer level of description that would consider the degrees of freedom for individual electrons. Since a macroscopic system has at least ~10^20 or so atoms, almost all the degrees of freedom are in the microscopic structure.

    When many creationists talk about the 2nd law of thermodynamics they make the mistake of overemphasizing the visible macroscopic structure. Believe it or not, there are many more ways of having a functioning car at 20°C than having a pile of car parts strewn about randomly at 19°C. The cooler car parts have a lower entropy, and the macroscopic order has such a small effect it doesn't even really enter the picture. This is because each atom is farther restricted at a cooler temperature, and the collective effect of this on ~10^25 atoms has a much bigger effect on the number of ways of arranging things than restrictions on how to arrange ~1000 parts.
     
  16. Jul 9, 2013 #15
    Very interesting.

    I share with creationists their (professed) desire to know how purposeful, organized macroscopic structures got to be the way they are. I think that's a perfectly valid thing to be interested in. But to say that they contradict the second law, and then when pressed say that, okay maybe they don't exactly contradict the second law but it's just so hard to see how they manage to satisfy it without intelligent intervention--that seems like a sneaky tactic. If they had been able to catch you off guard convince you that the second law is actually contradicted, they would just leave it at that and high five each other.

    Still, I learn a lot from looking at their stuff once in a while, whether directly or indirectly. They are highly motivated, often clever people. They spend a large part of their lives trying to dig up all sorts of odd facts that might be of use to them (and ignoring ones that aren't). And it is true that scientists sometimes engage in sloppy thinking themselves, or get some facts wrong, or talk confidently about stuff that they aren't well versed in, or say something in an unclear way. I can count on creationists to point these things out, and avoid the same pitfalls myself.
     
  17. Jul 9, 2013 #16

    LeonhardEuler

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    Yes, it's interesting to look at other points of view, and I read those arguments sometimes too. It is surprising and counter-intuitive that complicated things like people and other animals could arise out of matter following physical laws. But it definitely doesn't violate the laws of thermodynamics.

    Keep in mind that just because something doesn't violate the laws of thermodynamics doesn't mean it will happen. There are a lot of absurd things that won't happen, but don't violate the laws of thermodynamics, they violate other laws or are extremely improbable.

    An example I hear given by creationists is wind blowing through a junk yard and making an airplane. It is nearly impossible, but doesn't violate the laws of thermodynamics, but there are other reasons it is unlikely. They are better off leaving thermodynamics out of it and just arguing that it seems implausible. But we now know a process that can make really complicated things naturally, and that is evolution.
     
  18. Jul 10, 2013 #17
    There are ways to do it but ideally all relevant items should be cooled to about -5C for best results: glass slides and slide overs, clear thin superglue, and an artist's paintbrush. This article describes how. Even if the snow crystals eventually melt, you should have a "fossil". It's probably best to catch falling "dry" snow on a chilled piece of cardboard .

    http://www.its.caltech.edu/~atomic/snowcrystals/preserve/preserve.htm
     
    Last edited: Jul 10, 2013
  19. Jul 10, 2013 #18
    Thanks for the link. That site of Dr. Libbrecht's also has a link to a paper on snowflake physics that looks interesting. I have met Dr. Libbrecht and he is a cool guy. He didn't blow up when he found my me and my lab partner celebrating our partial success with a couple brewskies in the senior physics lab. He calmly suggested that it wasn't a great idea. We didn't do it again.

    Exactly. I am happy to admit that the natural emergence of complicated organizations defies my common sense. But I'm always having to improve my common sense. My common sense is not a law of nature. And as you say, something can be improbable for other reasons than defying a law of nature, in which case it would be impossible.

    In trying to imagine a universe where the popular "Everything's running down, getting worse" view of the second law would really apply in the way that some people think it does, I think the universe would need to consist of nothing but little billiard ball atoms. There would be no potential energy and no radiation. Only kinetic energy. So things could not clump together to form complex structures. A universe that started with a bunch of red balls separated from a bunch of white balls would proceed to a pinkish mixture of the balls, with no emergence of structure along the way. Fortunately the universe we live in is nothing like that.
     
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