c103-sp10-0512

# c103-sp10-0512 - Chemistry 103 Spring 2010 Today 1 State...

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Chemistry 103 Spring 2010 Today 1. State functions. 2. Redox reactions. Announcements 1. Ch. 14-17 OWL homework is active. 2. Next midterm exam on Wednesday, May 19. Chapter 16 and Chapter 17 (note 17.8-17.10 are mostly ideas) 3. CSULA closure on May 21 (furlough). 4. CSULA closure on May 31 (holiday). 5. Bring textbook and calculator to each lecture.

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Chemistry 103 Spring 2010 2 Review Δ Gº = -RTlnKº Calculate the equilibrium constant K c at 25 ºC from the standard free energy change for the reaction below. H 2 CO 3 (aq) H + (aq) + HCO 3 - (aq) Kº = 4.35 x 10 -7 = K c = K a = [H + ][HCO 3 - ]/[H 2 CO 3 ]
3 State functions and pathways Because changes in enthalpy, entropy, and free energy are state functions, we can use any pathway to calculate the change in enthalpy, entropy, and free energy of an overall reaction. Hess’s Law : Δ H for a process is equal to the sum of Δ H for any set of steps, i.e., for any path that equals the overall process. (also works for Δ G and Δ S because they are state functions, too) Often the steps are the formation reactions to make substances in their standard states. The Δ f , S° , and Δ f values for these reactions are easily determined through experiments: Δ rxn = Σ n Δ f (products) - Σ n Δ f (reactants) Δ rxn = Σ nS°(products) - Σ nS°(reactants) Δ rxn = Σ n Δ f (products) - Σ n Δ f (reactants) If we have data from other reactions, we could use those steps to build a different pathway to the overall reaction: Δ G ° rxn = Δ G ° rxn1 + Δ G ° rxn2 + … = Σ n Δ G ° rxns Δ S ° rxn

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## This document was uploaded on 03/06/2011.

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c103-sp10-0512 - Chemistry 103 Spring 2010 Today 1 State...

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