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Heat of Combustion help!

  1. Aug 12, 2007 #1
    1. The problem statement, all variables and given/known data

    Calculate the heat of combustion for C2H6 from the following information:
    C2H4+ 3O2----> 2 CO2 + 2 H2O (-1409.5kJ)
    C2H4 + H2 ----> C2H2 (-136.7 KJ)
    H2 + 1/2 O2 -----> H2O ( -285.5 kJ)





    3. The attempt at a solution

    C2H6 --> C2H4 + H2 +136.7kJ
    C2H4 + 302 --> 2CO2 + 2H20 -1409.5kJ
    C2H6 + 3O2 --> 2CO2 + 2H2O + H2 -1272.8kJ
    H2 + 1/2 O2 --> H2O -285.5Kj
    C2H6 + 3.5O2 --> 2CO2 + 3H2O - 1558.3kJ


    is my final answer 1558.3 correct?:confused: can someone check this for me plzz
     
  2. jcsd
  3. Dec 3, 2007 #2
    It is close.
    I have the following:
    C2H6 + 2.5O2 --> 2CO2 + 3H2O + DH
    Applying heats of formations for each compound:
    -85 + 2.5*0 = 2*(-394) + 3*(-242) + DH
    DH = 1429 kJ/mol

    You may use the following calculator http://home.fuse.net/clymer/rq/ but I found it not being very accurate.
     
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