Equilibria Dimensions - Equilibria, free energy and...

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Equilibria, free energy and constants. As I mentioned in class, the free energy of reaction, for say: 2 N 2 (g) + 6 H 2 O(g) 4 NH 3 (g) + 3 O 2 (g) would be: Δ G r ° = 3 Δ G f °(O 2 ) + 4 Δ G f °(NH 3 ) – 6 Δ G f °(H 2 O) – 2 Δ G f °(N 2 ) where Δ G f ° is the free energy of formation of the reactants and products in kJ/mol. Taking into account that Δ G f ° = 0 for elements in their standard state, we get Δ G r ° = 4 Δ G f °(NH 3 ) – 6 Δ G f °(H 2 O) for this reaction. Using numbers from your book Δ G r ° = 4 (-16.45 kJ/mol) – 6 (-228.75 kJ/mol) = 1306.7 kJ. This reaction as written produces 4 moles of NH 3 or 3 moles of O 2 . Also as written K P = ಿಹయ ೀమ ಿమ ಹమೀ and Δ G r ° =-RTln K P . But R is in units of J/K/mol. So while Δ G r ° = 1306.7 kJ, my RT ln K P would give me J/mol or kJ/mol. What happened to the number of moles? Why or how can we get the dimensions correct in the RT ln K P term? Remember how we wrote the balanced equation and the overall stoichiometry. The value of
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This note was uploaded on 11/19/2010 for the course CHEM 204 taught by Professor Gruebele during the Spring '08 term at University of Illinois, Urbana Champaign.

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Equilibria Dimensions - Equilibria, free energy and...

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