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Another HELP problem: Steam to Ice

  1. Nov 16, 2007 #1
    Another URGENT HELP problem: Steam to Ice

    1. The problem statement, all variables and given/known data

    How many J of energy must be removed when 127.0 g of steam, at a temperature of 153.0°C, is cooled and frozen into 127.0 g of ice at 0°C? Take the specific heat of steam to be 2.1 kJ/(kg·K).

    2. Relevant equations
    Q1 = mc(delta T) <---- c= heat capacity of steam
    Q2 = mLv
    Q3 = mc(deltaT)<---- c=heat capacity of water
    Q4 = mLf

    3. The attempt at a solution

    first I converted grams to kilograms and got .127kg for the mass then I follwed through with my equations
    Q1 = (.127)(2100)(153-100)= 1.4135E4
    Q2 = (.127)(2259.36)= 2.869E2
    Q3 = (.127)(4186)(100-0)= 5.316E4
    Q4 = 4.241E4

    I added these up and got a total Q of 1.10E5, what am I doing wrong?
  2. jcsd
  3. Nov 16, 2007 #2


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  4. Nov 16, 2007 #3
    he had a different problem (that is to say a different problem regarding the same problem) than me, I just need to know if I'm doing it right and when went wrong.
  5. Nov 16, 2007 #4


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    You have the constants wrong.
    specifically the heat of vapourisation - the water/steam change should be the largest energy.
    Just put you hand over a kettle to find out!
    Last edited: Nov 16, 2007
  6. Nov 16, 2007 #5


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    Staff: Mentor

    Please check units!

    I strongly recommend writing units with values, so that one properly accounts for orders of magnitude.
  7. Nov 16, 2007 #6
    I seriously don't know how I keep messing up my units, but thanks again.
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