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Gibbs Free energy

  1. Nov 4, 2013 #1
    1. The problem statement, all variables and given/known data


    When gaseous nitrogen and hydrogen are converted to gaseous ammonia, then delta G equals: -16.64Kj/mol

    3h2+ n2=2nh3
    Using the s values , calculate the delta h for the formation of ammonia

    2. Relevant equations

    Delta s for:
    H2:130.6
    N2:191.5
    Nh3:192.5

    T= 298

    3. The attempt at a solution

    Delta h= delta G + T delta s

    The ans is 46.2 kj/mol for NH3

    I understand how to get the delta s values
    However how did they get 46.2

    In the ans, they multiplied delta g by 2
    And then after adding it to the T delta s
    They got 92.3 Kj and divided it by 2 mols to get 46.2

    My question is why are they multiplying delta G by 2?
     
  2. jcsd
  3. Nov 5, 2013 #2

    Borek

    User Avatar

    Staff: Mentor

    Most likely data given

    is per mole of ammonia produced, not per so called "mole of reaction". Thus, as in a "mole of reaction" two moles of ammonia are made, you need to multiply by 2.

    But if that's the case it should be clearly spelled out what the data refers to, otherwise question is ambiguous. Nothing wrong with listing values per mole of substance or mole of reaction, as long as it is clear which one is given.
     
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