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Outline: 2/19/07

Outline: 2/19/07. Pick up Exam #1 - from me Pick up CAPA #10 & 11 - outside Seminar – Tues @ noon Jaecker Applications – Chem Dept . Today: Chapter 16 . Chemical Equilibrium The Equilibrium Constant (K eq ) Manipulating/Calculating K eq. Exam #1. Average ~ 74.7

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Outline: 2/19/07

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  1. Outline: 2/19/07 • Pick up Exam #1 - from me • Pick up CAPA #10 & 11 - outside • Seminar – Tues @ noon • Jaecker Applications– Chem Dept. • Today: Chapter 16 • Chemical Equilibrium • The Equilibrium Constant (Keq) • Manipulating/Calculating Keq

  2. Exam #1 • Average ~74.7 • High: 99,… Well done! • 15 25 35 45 55 65 75 85 95

  3. Exam #1 • What to do if…. Go over test = do a post mortem Remember it’s only 20%...or less! Change something… Come visit…

  4. Chapter 16: Equilibrium • 2 NO2(g) N2O4(g) • Rateformation = kf[NO2]2 • N2O4(g) 2 NO2(g) • Ratedecomposition = kd[N2O4] • At equilibrium: Ratef = Rated • kf [NO2]2 = kd[N2O4]

  5. nomenclature: [concentrations] or p •  becomes  • Rxn quotient: Q = [products]/[reactants] • Define an “equilibrium constant”: • Keq= kf /kd = [N2O4]/[NO2]2 • e.g. IfQ = Keq system is at equilibrium • IfQ > Keq products  reactants • IfQ < Keq reactants  products

  6. The Equilibrium Constant • For a general reaction • the equilibrium constant expression for everything in solution is • where Keq is the equilibrium constant.

  7. The Equilibrium Constant • An equilibrium can be approached from any direction. • Example: • has

  8. The Equilibrium Constant • In the reverse direction:

  9. Equilibrium Constant Rules: Magnitude of Keq tells you about preferred direction of reaction Keq = 31000 or Keq = 4.610-8 more products (at equilibrium) more reactants

  10. Equilibrium Constant Rules: Reactions can be written in either direction at equilibrium Keq = 1/ K’eq Reactions can be written as the sum of other reactions (Hess’ law) Keq = K’eq K”eq

  11. AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl- • Keq = A specific example (chem 113): • AgCl(s) Ag+ + Cl- Keq = 1.8  10-10 • Ag+ + 2 NH3 Ag(NH3)2+ • Keq = 1.6  107 • Keq = 2.9  10-3

  12. Equilibrium Constant Rules: Solids and (pure) liquids are left out of the Keq expression Example: H3PO4(aq) + 3 H2O(l) PO3-4(aq) + 3H3O+(aq) Keq = [PO3-4 ] [H3O+]3/ [H3PO4]

  13. Equilibrium Constant Rules: Magnitude of Keq tells you about the extent of reaction Reactions can be written in either direction at equilibrium Solids and (pure) liquids are left out of the Keq expression Units of Keq are defined to be 1….

  14. Let’s Practice: Worksheet #6 (A) Keq = (pNO)2(pO2) / (pNO2)2 = (0.0015)20.051 / (0.1)2 = 1.15e-5

  15. Starting from initial concentrations: • Mix: 110-3 Fe3+ and 110-3 SCN- • Keq = 142 • What are the final concentrations? • 110-3 110-3 0 Initial • -x -x +x Change (110-3-x)(110-3-x) +x Equil. • Fe3+ + SCN- Fe(SCN)2+

  16. Initial concentrations: • Mix: 110-3 Fe3+ and 110-3 SCN- • What are the final concentrations? • Keq = [Fe(SCN)2+]/[Fe3+][SCN-] • 142 = x / (110-3-x) (110-3-x) • (a quadratic equation in x) • x = 1.1110-4

  17. Return to Worksheet #6 • Do problems B & C Practice these! Finish Friday

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