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Thermochemistry Help Again! How to find mass?

  1. Feb 10, 2010 #1
    1. The problem statement, all variables and given/known data

    Imagine that your water heater has broken, but you want to take a bath. You fill your bathtub with 25 kg of room-temperature water (about 25 degrees Celsius). You figure that you can boil water on the stove and pour it into the bath to raise the temperature. How much boiling water would you need in order to raise the bath to body temperature (about 37 degrees Celsius)? Assume that no heat is transferred to the surrounding environment.

    2. Relevant equations

    q = mc(Tf-Ti)

    3. The attempt at a solution

    So I find "q" in the following way:

    q = 25000 g x 4.18 J/g x C x 12 C
    q = 125400 J/g x C

    Then, I sub in the following...

    m = q/c(Tf-Ti)
    m = 125400 J/g x C / 4.18 J/g x C x 12 C
    m = 2500

    I have a strong feeling this is terribly wrong, can someone please point the mistake out for me?
     
  2. jcsd
  3. Feb 11, 2010 #2

    Lok

    User Avatar

    What is that "q = 25000 g x 4.18 J/g x C x 12 C", and why find out the energy of the water?
    The specific heat of water between 0 and 100 is about the same.(usually regarded)

    So you have 25kg -- 25'C
    x kg -- 100'c
    And the 25+x kg -- 37'C

    Can you get an equation from these?
     
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