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Find amount of water at 20 degrees to melt 100 g ice

  1. Nov 9, 2013 #1

    vtl

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    This an extra voluntary question on a physics assignment I've already handed in. But I still want to try and figure it out so here goes:


    1. The problem statement, all variables and given/known data
    This is what I'm told: "You take 100 g ice cubes from the freezer. The ice cubes' temperature is -18°C." The specific heat capacity of ice is 2,0 kJ/kg*K.

    And then asked: "How big an amount of water at 20°C is required to melt the ice cubes from the freezer?"


    2. Relevant equations
    Qwater = cmΔT
    Qice = mL

    cwater*mwater*∆Twater+mice*Lmelt+cwater*mice*∆Tice=0

    3. The attempt at a solution
    I assume I need to find L, because in the examples in the book the L's used are for materials at either 0°C or 100°C, which I've isolated:

    -Lmelt=(cwater*mwater*∆Twater)/(-mis )+(cwater*mice*∆Tice)/(-mice )

    The problem is that I also don't know mwater because that's what the problem asks me to find. Will any amount of 20°C hot water melt the ice cubes eventually or something?
     
    Last edited: Nov 9, 2013
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  3. Nov 9, 2013 #2

    haruspex

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    You don't mention the water temperature in the problem statement. That's needed. You mention 20C later - is that given, or a number out of the air?
    What temperature do you think the ice will be at just before it melts?
     
  4. Nov 9, 2013 #3

    vtl

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    That's because there are three questions attached to the problem statement. 20 degrees is the temperature of the water you use to melt the ice.

    0 and 100 degrees is not related to the temperature of the ice, but of the water used to melt the ice.


    Edit: forgot to mention the 20 degrees when I translated the problem.
     
  5. Nov 9, 2013 #4

    haruspex

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    Then I don't understand what that has to do with L. You wrote
    L stands for latent heat, right? The latent heat of fusion of ice is nothing to do with the temperature of the water used to melt it. It's a constant which you can just plug in.
     
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