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Homework Help: Standard enthalpies of a reaction

  1. Dec 14, 2009 #1
    I calculated the standard enthalpy of a reaction using the constituent standard enthalpies of formations. My answer is in kcal / mol, how do I convert to J/g ?
    I know how to do the unit analysis BUT

    for the weight in grams... I imagine I use the weight in grams of the reaction - right? Would that be the combined weight in grams of the products or the net difference (in grams?)?


    example, calculating the enthapy of the following reaction:
    CuSO4•5H2O(s) → CuSO4•3H2O(s) + 2H2O(g)

    literature values in kcal/mol :
    CuSO4•5H2O(s) ΔHf = -544.45
    CuSO4•3H2O(s) ΔHf = -402.27
    H2O(g) ΔHf = -57.80

    When I convert each one to J/g, I get an enormous enthalpy of reaction (about -26000) but it should be about +500!!!!!!!!!
    Last edited: Dec 14, 2009
  2. jcsd
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