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11-10-09 - GibbsFreeEnergy Gsys = Hsys Tsys Ssys < 0...

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Gibbs Free Energy G sys = H sys T sys S sys G = H - T S < 0 → spontaneous > 0 → not spontaneous = 0 → at equilibrium
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Gibbs Free Energy,  G G o = H o - T S o Two methods of calculating ∆ G o a) Determine ∆ H o and ∆ S o and use Gibbs equation. b) Use tabulated values of free energies of formation, ∆ G o f . Gibbs equation
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Free Energies of Formation Note that ∆G Note that ∆G o f for an element = 0 for an element = 0 G o = ∑ ∆ G o f (products) - ∑ ∆ G o f (reactants)
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C ( graphite ) + 2 H 2 (g) CH 4 (g) Example: Is the following reaction spontaneous at 298 K ? -50.8 186.26 -74.87 0 130.7 0 0 5.6 0 C ( graphite ) H 2 (g) CH 4 (g) G o f (kJ/mol) H o f (kJ/mol) S o (J/mol.K)
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Tungsten (W) filament
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Tungsten filament Glass
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W atom
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High temperatu Not so high temperature
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High temperatu Not so high temperature Br 2 molecule
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High temperatu Not so high temperature WBr 5 molecule
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High temperatu Not so high temperature
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High temperatu Not so high temperature
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High temperatu Not so high temperature
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W ( g ) + 2½ Br 2 ( g ) WBr 5 ( g ) WBr 5 ( g ) W ( g ) + 2½ Br 2 ( g ) At “moderate” T: At “high” T:
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