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Unformatted text preview: 19.7 Thermodynamics and Keq G, G, and Keq
G is change in free energy at non-standard conditions. G is related to G G = G + RT ln Q where Q = reaction quotient When Q < K or Q > K, reaction is spontaneous. When Q = K reaction is at equilibrium When G = 0 reaction is at equilibrium Therefore, G = - RT ln K G, G, and Keq
Product Favored, G negative, K > 1 G, G, and Keq
Product-favored 2 NO2 ---> N2O4 Gorxn = 4.8 kJ State with both reactants and products present is more stable than complete conversion. K > 1, more products than reactants. G, G, and Keq
Reactant-favored N2O4 --->2 NO2 Gorxn = +4.8 kJ State with both reactants and products present is more stable than complete conversion. K < 1, more reactants than products Thermodynamics and Keq
Keq is related to reaction favorability. When Gorxn < 0, reaction moves energetically "downhill" Gorxn is the change in free energy when reactants convert completely to products. Thermodynamics and Keq
Gorxn is the change in free energy when pure reactants convert completely to pure products. Product-favored systems have Keq > 1. Therefore, both Grxn and Keq are related to reaction favorability. Thermodynamics and Keq
Keq is related to Gorxn. The larger the value of K the more negative the value of Gorxn Gorxn = - RT lnK where R = 8.31 J/Kmol Thermodynamics and Keq
Gorxn = - RT lnK
Calculate K for the reaction N2O4 --->2 NO2 Gorxn = +4.8 kJ Gorxn = +4800 J = - (8.31 J/K)(298 K) ln K 4800 J ln K = = - 1.94 (8.31 J/K)(298K)
K = 0.14 When Gorxn > 0, then K < 1 ...
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This note was uploaded on 04/07/2008 for the course CHEM 120 taught by Professor Tucker during the Spring '08 term at Siena College (Loudonville).
- Spring '08