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Gibbs Free Energy & Equilibrium Constants. 19.7-8. K: Equilibrium Constant. For a general reaction: aA + bB --> cC + dD K = [C] c [D] d [A] a [B] b. K >1 product favored K <1 reactant favored. Equilibrium Molarities or Pressures of R/P.
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K: Equilibrium Constant • For a general reaction: aA + bB --> cC + dD • K = [C]c[D]d [A]a[B]b K >1 product favored K <1 reactant favored Equilibrium Molarities or Pressures of R/P
Gibbs Free E and Equilibrium Constant • Gº = − RT lnKeq - R: ideal gas constant, 8.314 J/mole·K - T: Kelvin - K: value of equilibrium constant
∆G° and K • At equilibrium: Gº = − RT lnKeq • If G < 0, then K > 1; product favored • If G = 0, then K = 1; the rx is at equilibrium. • If G > 0, then K < 1; reactant favored
Practice Problems • For a reaction, the G = -16.37 kJ/mol. Calculate the equilibrium constant at 25 C. P or R favored? • For a reaction, the K = 1.8 x10-10. Calculate Gº. P or R favored?
Bond Dissociation Energy [Ch 9: pp.355-357] • The enthalpy change for breaking a specific type of bond in a molecule • Breaking bonds is endothermic; forming bonds is exothermic • ∆H°rxn = Energy to break bonds - Energy to form Bonds
Bond Dissociation Energy • Estimate the enthalpy for the combustion of propane • C3H8 + O2 --> CO2 + H2O Bond: Ave bond diss. energy in kJ mol-1 C-H +413 C-C +347 O=O +498 C=O +805 H-O +464 All endothermic
Bond: Ave bond diss. energy in kJ mol-1 C-H +413 C-C +347 O=O +498 C=O +805 H-O +464
