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Heat/fusion/vaporization question?

  1. Aug 17, 2010 #1
    1. The problem statement, all variables and given/known data
    Given 150g of ice at -15oC, how much steam (at 100oC in g) is required to give a resultant of 50oC water?


    2. Relevant equations
    q=lm
    q=cmT
    heat for vap: 2256j
    heat for fusion: 333J


    3. The attempt at a solution
    I got something like
    remaining heat: 49950-2256m
    change heat with remaining water: 4.19(150+m)T
    and that m(100)/(150+m)=50 (error here?)

    In the end, i got something like m=9g, which is too little, cause answers says 33g
     
  2. jcsd
  3. Aug 18, 2010 #2

    kuruman

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    What exactly is your reasoning for this "remaining heat"? What is 49950 and how did you get it?
     
  4. Aug 19, 2010 #3
    remaining heat: 49950-2256m

    I got this from q=lm
    where 49950 is the joules taken to melt ice to liquid, and 2256m (where m is the mass of gas) is the joules given off to turn steam to liquid.
     
  5. Aug 20, 2010 #4

    kuruman

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    When you end up with water at 50 oC, you need to say that the heat lost by the steam is equal to the heat gained by the ice. In other words,

    Heat to turn steam to liquid + Heat to reduce T of condensed steam from 100 oC to 50 oC

    is equal to

    Heat to turn ice to liquid + Heat to raise T of melted ice from 0 oC to 50 oC.
     
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