Energy of reaction: per moles of what?

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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!
 

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  • #2
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1 mole of thiosulfate
Generally per mole of the principal reactant. You winkled it out.
 
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Generally per mole of the principal reactant. You winkled it out.
Thanks for the reply! How do I determined which is the principal reactant if I'm not familiar with the reaction?
 
  • #4
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which is the principal reactant if
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.
 
  • #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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