Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted