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Ch. 9 K&K: Gibbs Free Energy and Chemical Reactions

Ch. 9 K&K: Gibbs Free Energy and Chemical Reactions. Recall (ch. 8): Free energy conditions . Helmholtz F isothermal Enthalpy H constant pressure Gibbs G const. pressure and temp.

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Ch. 9 K&K: Gibbs Free Energy and Chemical Reactions

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  1. Ch. 9 K&K: Gibbs Free Energy and Chemical Reactions Recall (ch. 8): Free energy conditions . Helmholtz F isothermal Enthalpy H constant pressure Gibbs G const. pressure and temp

  2. Ch. 9 K&K: Gibbs Free Energy and Chemical Reactions Recall (ch. 8): Free energy conditions . Helmholtz F isothermal Enthalpy H constant pressure Gibbs G const. pressure and temp Recall (ch. 3) pg. 68: “The Helmoltz free energy will be a minimum for a system S in thermal contact with a reservoir R if the volume of the system is constant.”

  3. Gibbs free energy Chemical reactions (and other experiments) are often carried out at constant pressure and constant temperature: (Gibbs free energy; Thermodynamic potential) G(U,t,s,P,V) = U – ts + PV

  4. Gibbs free energy Chemical reactions (and other experiments) are often carried out at constant pressure and constant temperature: (Gibbs free energy; Thermodynamic potential) G(U,t,s,P,V) = U – ts + PV dG = dU – tds – sdt + PdV + VdP

  5. Gibbs free energy Chemical reactions (and other experiments) are often carried out at constant pressure and constant temperature: (Gibbs free energy; Thermodynamic potential) G(U,t,s,P,V) = U – ts + PV dG = dU – tds – sdt + PdV + VdP Isothermal dt = 0 Isobaric dP = 0 So, for a system S at equilibrium: dGS = dUS – tdsS + PdVS

  6. dG = 0 at equilibrium dGS = dUS – tdsS + PdVS Comparing to eqn. 5.39 (dUS = tdsS – PdVS + mdNS) shows dGS = mdNS = 0, since dNS = 0 at equilibrium

  7. Chemical reactions in equilibrium H2 + Cl2 = 2HCl n1A1 + n2A2 + n3A3 + ….nmAm = 0 A1 = H2n1 = 1 A2 = Cl2n1 = 1 A3 = HCl n1 = -2 SnjAj = 0

  8. Chemical reactions in equilibrium Want to find expression of chemical equilibrium under conditions of constant temperature and pressure dG = SmjdNj j The unknown details of the chemical reactions are summarized by the various chemical potentials.

  9. Chemical reactions in equilibrium At equilibrium, dG = 0

  10. K(t) for an ideal gas with internal degrees of freedom

  11. K(t) for an ideal gas with internal degrees of freedom

  12. K(t) for an ideal gas with internal degrees of freedom

  13. K(t) for an ideal gas with internal degrees of freedom

  14. K(t) for an ideal gas with internal degrees of freedom

  15. K(t) for an ideal gas with internal degrees of freedom

  16. K(t) for an ideal gas with internal degrees of freedom

  17. Chemical reaction rates

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