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Need help with simple calorimetry problem

  1. Apr 18, 2005 #1
    So here's the problem

    Conside the dissolution of CaCl2:

    CaCl2(s) ---> Ca^(2+) (aq) + 2Cl^(-1) (aq) deltaH = -81.5kJ

    An 11.0g sample of CACl2 id dissolved in 125g of water, with both substances at 25.0°C. Calculate the final temperature of the solution assuming no heat lost to the surroundings and assuming the solution has a specific heat capacity of 4.18 J/(°C*g).


    So far I think it's just q(rxn) = q(water) + q(CaCl2)

    (136g)(4.184J/°Cg)(Tfinal - 25.0°C) = (125g)(4.184)(Tfinal - 25.0°c) + (11g)c(Tfinal - 25.0°C)

    But it seems that I am missing C for the calcium chloride and I don't know what to do about it? is there another way to calculating it without C of CaCl2?
     
  2. jcsd
  3. Apr 19, 2005 #2
    The heat capacity(Cp) of the solution will be very close to that of pure water, 4.18 J/(g C). The problem states this.
     
  4. Apr 19, 2005 #3
    Are you suggesting that I use 4.184 for the heat capacity of every one? If I do then it wouldn't make sense since that's just making the left side equal to the right side and getting at final temperature of 25.0°C.

    By the way, is my formula correct though?

    heat of solution = heat of water + heat of calcium chloride
     
  5. Apr 19, 2005 #4

    GCT

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    You won't need the left side of this equation. Note that the enthalpy is in kJ/mole of reaction. How would you convert kJ/mole of reaction to kJ?

    This energy is equivalent to q...it is used to raise the temperature of ___?

    "(136g)(4.184J/°Cg)(Tfinal - 25.0°C)",

    this is incorrect, 4.184J/Cg applies specifically to water.
     
    Last edited: Apr 19, 2005
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