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Energy of reaction: per moles of what?

  1. Jan 10, 2015 #1
    Disclaimer: I've never had a chemistry class in my life. I'm reading a journal article that states the following:

    S2O32- + 2O2 + H2O → 2SO42- + 2H+

    has the standard Gibbs energy of −766 kJ/mol at 25ºC. So, this is energy produced per moles of what?! Reactant? Product? If so, which reactant or product and how do I figure that out? Or does it just mean that if I reacted 1 mole of thiosulfate with 2 moles of oxygen, I'd end up with 766 kJ of energy? Any help would be appreciated!
     
  2. jcsd
  3. Jan 10, 2015 #2

    Bystander

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    Generally per mole of the principal reactant. You winkled it out.
     
  4. Jan 10, 2015 #3
    Thanks for the reply! How do I determined which is the principal reactant if I'm not familiar with the reaction?
     
  5. Jan 10, 2015 #4

    Bystander

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    Hopefully there's some context to point it out. Look for key phrases hidden in obscure places in the text, "per mole of _____" produced/consumed.
     
  6. Jan 10, 2015 #5

    Borek

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    If there is no other information - "per mole of reaction as written". Say you are told ΔH for

    2Al + 3Cl2 → 2AlCl3

    is x kJ. That would mean x/2 kJ per mole of Al consumed or AlCl3produced, x/3 kJ per mole of Cl2.
     
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