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Homework Help: Hess's law Help

  1. Dec 5, 2009 #1
    I have a problem I can't seem to solve. here it is and here is what I have gotten.

    Iron metal is produced in a blast furnace through a complex series of reactions the involve reduction of iron(III) oxide with carbon monoxide

    a. Write a balanced overall equation for the process, including the other product.

    Fe2O3(s) + 3 CO(g) → 2 Fe(s) + 3 CO2(g)

    b. Use the equations below the calculate ∆H of rxn for the overall equation:

    3Fe2O3(s) + CO(g) → Fe3O4(s) + CO2(g) ∆Ho = -48.5 kJ

    Fe(s) + CO2(g) → FeO(s) + CO(g) ∆Ho = -11.0 kJ

    Fe3O4(s) + CO(g) → 3FeO(s) + CO2(g) ∆Ho = 22.0 kJ

    This what I come up with, i get 2/3 Fe3O4 on one side and 1/3 Fe3O4 on the other side giving me a 1/3 of Fe3O4 that dose not cancel each other out.

    Fe2O3(s) + 3 CO(g) → 2 Fe(s) + 3 CO2(g) ∆H= ?
    Fe2O3(s) + 1/3CO(g) → 1/3Fe3O4(s) + 1/3CO2(g) ∆Ho = -16.17kJ
    2FeO(s) + 2CO(g) → 2 Fe(s) + 2CO2(g) ∆Ho = +22.0 kJ
    2/3Fe3O4(s) + 2/3CO(g) → 2FeO(s) + 2/3CO2(g) ∆Ho = +14.67 kJ
  2. jcsd
  3. Dec 6, 2009 #2
    You don't really need 4 equations, just stick with those you got. Try again using the three equations given to you. When you have done it is like you say Fe3O4 is not going to cancel each other out but remember that is ok to multiply a equation with a number. It is easier when you avoid fractions.
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