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Y ICE doesnt melt when placed in microwave oven?

  1. Nov 2, 2009 #1
    i was dumbstruck :bugeye: :surprised after hearing the statement "that ice didn't melt when placed in microwave" from one of my friend, and its indeed true i checked by myself.And now i'm looking for the reason :)
     
  2. jcsd
  3. Nov 2, 2009 #2

    A.T.

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    I guess the water molecules are not dipoles anymore, when bound within a crystal structure, via hydrogen bonding.
     
  4. Nov 2, 2009 #3
    As far as I understand ,when in the liquid state the absorbed microwave energy is converted into molecular movement of the polar water molecules this giving rise to heating.In the solid state the molecules are strongly attracted to other molecules this severely restricting their movement.The ice will melt, it just takes time.
     
  5. Nov 2, 2009 #4
    I just put in 4 icecubes on a plate at full power. They were completely melted after 90 seconds.
     
  6. Nov 2, 2009 #5

    Cleonis

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    I do know that the microwave radiation provides a resonant frequency for transitions in rotation state of the water molecules. I assume that interaction with the microwaves whips the water molecules into spinning motion. When such a spinning water molecule collides with another molecule the rotational kinetic energy converts to other kinetic energies. That is, energy is pumped into the assembly of water molecules in the form of rotational kinetic energy of individual molecules, and subsequently that energy becomes distributed over all the possible motions of the molecules; the water heats up.

    I think that when water is in ice-form there is no transition available that resonates with the microwaves. Presumably only the water molecules on the surface of the ice are free enough to interact with the microwaves. So initially ice will absorb almost as little of the microwave's energy as, say, glass does.

    As more and more water transits from ice to water form there is more and more opportunity to absorb energy from the microwaves.

    Cleonis
     
  7. Nov 2, 2009 #6
    This question is similar to "Why water does not boil when placed in microwave oven"?
    It heats anyway and with time it melts and boils.
     
  8. Nov 2, 2009 #7

    D H

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    Water has a rather high heat of fusion. It takes quite a bit of energy (333.55 kilojoules/kilogram) to convert ice at 0°C to liquid water at 0°C. The same amount of energy applied to liquid water initially at 0°C will raise the temperature of that water to about 80°C.
     
  9. Nov 2, 2009 #8
    Quite right, heating water in a microwave is all fine and dandy until you take it out and put a spoon in.

    Exploding water is acutally quite a sight.
     
  10. Nov 2, 2009 #9
    That should be a quite pure water, distillated or so.
     
  11. Nov 2, 2009 #10
    And in a very smooth beaker
     
  12. Nov 2, 2009 #11

    D H

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    Yes, but the recent discussion on superheating of water misses the point to some extent. The reason water does not melt or boil (easily) is because of the latent heats of fusion and vaporization of water. It takes about the same time to raise liquid water from 0°C to 100°C as it does to change ice at -40°C to liquid water at 0°C, and it takes even longer (a lot longer) to completely boil liquid water that is already at 100°C.
     
  13. Nov 2, 2009 #12
    This is the tricky thing about people not realising the difference between heat and temperature.

    a t-s diagram would help.... (maybe)??
     
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