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Two quick questions

  1. May 9, 2005 #1
    Three quick questions

    1) Is there a (safely!) edible liquid whose viscosity is less than that of water?

    2) Why must pressure be applied to freeze helium? (rather than just temperature like the other noble gases)
    (sorry, 3rd question just came from second :shy: )
    3) Because of question #2, I assume that not all gases liquefy before reaching absolute zero. Right?? (or wrong?)
    Last edited: May 9, 2005
  2. jcsd
  3. May 10, 2005 #2


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    1) I know of none. Water has a pretty low viscosity. Close or lower, are the light alcohols : methanol (which will make you blind in a few sips) and ethanol (which has methanol as the primary impurity). Neither of these is safely edible.

    2) Pressure must be applied (from vacuum) to freeze any gas at 0K. Keep in mind that the pressure merely fixes the mean spacing between molecules. For different gases, the pressure at which it solidifies is different and depends on the size of the atoms/molecules and the strength of the interactions between them. For He, the interactomic interaction is weaker than for the other noble gases, so it takes a higher pressure to solidify it. It just happens that this pressure is greater than 1 atm for He, and less than 1atm for the other gases. But remember that 1 atm is essentially an arbitrary pressure (determined by the mass and radius of the earth and the the gases in the atmosphere), so there's nothing special about it in this context.

    3) Again, it depends on the pressure. If you have a large room at 0K filled with say a 1000 molecules of any element/compound (and nothing else), you will not have a liquid. If you increase the pressure by shrinking the room into a tiny ball a few nanometers in diameter, you will make a liquid. Shrink further, and you have a solid !

    Extra note : It's really evasive to talk about liquid and solid helium at 0K without getting into a discussion of Bose Einstein Condensation. At this level, however, such a discussion is unwarranted.
  4. May 10, 2005 #3
    Is helium the ONLY gas that requires pressures above 1 atm to liquefy before reaching absolute zero ?

    But...is it possible to make a safely edible liquid with a viscosity less than that of water ? Is it impossible :confused: ?

    Basically, if I see a label that says "liquid's viscosity is less than that of water" on a bottle of liquid, then generally it would be dangerous to drink the liquid in the bottle?
    Also, what are some of the properties of "liquid helium" ???
    Last edited: May 10, 2005
  5. May 11, 2005 #4
    The only pure substance (not a mixture) liquids at room temperature and pressure I know of that are not harmful to humans in anything more than small amounts are going to be water and certain organic oils, which definitely have a higher viscosity. This is because oil is the only liquid which your body naturally digests. Anything else is going to have some toxic effect, because it is going to interfere with chemical reactions in your body which are dependent on a high concentration of water. Interfering with this concentration blocks or upsets the equilibrium of natural chemical reactions that go on in your body, and may react with other substances in your body which produce toxins which kill cells. Concentrated ethanol in small amounts that does not have methanol impurities will not kill you but is pretty harmful. Concentrated (95%) ethanol for use in industrial/chemical settings is sold as "denatured" ethanol with methanol impurities, which render it unsuitable for human consumption, for the purpose of avoiding taxes on "potable" alcohol.
  6. May 11, 2005 #5
    So ALL liquids with a viscosity less than water are harmful ?

    And my second question :smile: :

    What are the properties of liquid helium ?
  7. May 11, 2005 #6
    Yes, depending on the amount.

    Liquid helium exhibits superfluidity at low temperatures. This gives it very unique and strange properites - for instance there is a huge jump in specific heat at 2.18 K You can find more http://en.wikipedia.org/wiki/Superfluid
    and http://en.wikipedia.org/wiki/Liquid_helium

    Note that there is a difference in behavior between Helium-4 and its rarer isotope Helium-3. Helium-4 has a total spin of 0, so it is a boson and behaves Bose-Einstein statistics. Helium 3 on the other hand, has a net nuclear spin of 1/2, which makes it a fermion and behavs Fermi-Dirac statistics. Because of the difference in statistical thermodynamic behavior, the freezing point of helium-3 is 0.002 K compared to 4.18 k for helium-4.
  8. May 11, 2005 #7


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    Would you please confirm that this is accurate ?
  9. May 16, 2005 #8
    You're right, I meant to say "boiling point" and its 3.2 K for helium-3. 0.002 K is the point at which helium-3 exhibits superfludity, while helium-4 exhibits superfluidity at 2.2 K (the lambda point).
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