L29-post

# L29-post - 1 Lecture 29 How Far Gibbs Free Energy Key Idea...

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Unformatted text preview: 1 Lecture 29 How Far? Gibbs Free Energy Key Idea: The amount of product depends on the magnitude and sign of the enthalpy and entropy changes. ∆ G o Temp ∆ G o Temp ∆ G o Temp ∆ G o Temp From Wednesday: ∆ G o = ∆ H o − T ∆ S o ∆ H o ∆ S o − + ∆ H o ∆ S o + − ∆ H o ∆ S o + + ∆ H o ∆ S o − − Types of Problems to Solve in Chem 1A 1. Calculate the standard Gibbs free energy change ( ∆ G o ) at 298.15 K for a reaction in two different ways: (a) from the Gibbs free energies of formation ( ∆ G o f ), and (b) from ∆ H o rxn and ∆ S o rxn . 2. From this information, determine if a reaction is product-favored or reactant-favored at the standard temperature (298.15K). For a reaction that is reactant-favored, calculate the temperature above or below which the reaction becomes product-favored. 2 Mg (s) + CO 2 (g) → 2 MgO (s) + C (graphite, s) Mg (s) CO 2 (g) MgO (s) C (graphite,s) ∆ H o f S o ∆ G o f-393.5-601.7 32.68 213.74 26.94 5.74-394.4-569.43 in kJ/mol in J/mol K in kJ/mol N 2 O 4 4 (g) (g) 2 NO NO 2 (g) g) Predict ∆ H o : Predict ∆ S o : 51.31 240.06 33.18 NO 2 (g) 97.89 304.29 9.16 N 2 O 4 (g) ∆ G° f S° ∆ H° f in kJ/mol in J/mol K in kJ/mol N 2 O 4 4 (g) (g) 2 NO NO 2 (g) g) ∆ G o = ∆ H o − T ∆ S o = +57,200 J − 298.15 K (+175.83 J/K) = +57,200 J − 52,424 J ∆ G o Temp ∆ H o ∆ S o + + Recall Le Chatelier’s Principle!...
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L29-post - 1 Lecture 29 How Far Gibbs Free Energy Key Idea...

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