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Homework Help: [A-level]Latent Heat Question, Help!

  1. Jan 12, 2010 #1
    1. The problem statement, all variables and given/known data
    The specific latent heat of vaporization of water at 28[tex]\circ[/tex]C is 2.3 x 106JKg-1. It has been estimated that 1.2 x 1012 m3 of water is evaporated per day from the Earth's surface.

    Given that the density of water is 1 x 103 kgm-3calculate the energy required to evaporate this volume of water.

    3. The attempt at a solution

    I'm thinking since the water is just evaporating and not boiling, the energy needed would be the heat required to just evaporate the water:

    EH=mwater x latent heat
    =2.67 x 1018J

    But this is wrong. I realize I have not used the density of water but I do not know how to apply it. Is this question asking me to find the increase in internal energy?

    In any case the volume of water is 1.02 x 109m3.
  2. jcsd
  3. Jan 12, 2010 #2


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    Homework Helper

    What did you use for the mass of water? You need to find the mass using mwater=ρV
  4. Jan 12, 2010 #3

    I cannot believe I made such a silly mistake. For some reason I always saw the volume as the mass.

    Anyways I got the correct answer now. Thanks.
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