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Homework Help: Enthalpy of Reaction

  1. Oct 6, 2008 #1
    Hi. It's my first time posting here. I did a quick search, but I couldn't find any existing threads addressing my question, so here it is:

    Fe2O3 (s) + 3 C (gr) --> 4 Fe (s) + 3 CO2 (g)

    What is the ΔH of formation of CO2 (g) at 298 K if the following is true of the above reaction at 298 K:
    • Keq = 5.80 x 10-53
    • ΔSorxn = 0.522 kJ/K
    • ΔHoformation of Fe2O3 (s) = -795 kJ/mol

    I know that the correct answer is -114 kJ/mol, but I can't figure out how to get there. Here's what I've done so far:

    ΔGo = -RT lnK

    ΔGo = ΔHo -TΔSo
    ΔHo = -298kJ + (298K)(.522kJ/K)
    = -142.44 kJ

    -142.44kJ = 3ΔH (CO2) - 795 kJ
    3ΔH (CO2) = 652.5 kJ
    ΔH (CO2) = 217.5 kJ

    Which obviously isn't the right answer, but I don't see where I went wrong. Anybody see what I don't?
  2. jcsd
  3. Oct 7, 2008 #2


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    Science Advisor
    Homework Helper

    The reaction is not balanced , and next your last portion of work is wrong.
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