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Chapter 14

Chapter 14. Equilibrium Suroviec Spring 2014. I. Equilibrium. So far we have mostly considered just forward reactions aA + bB  cC + dD. But all reactions can move in either direction. A. State of equilibrium. Rate of equilibrium. Equilibrium is dynamic. B. Positions of equilibrium.

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Chapter 14

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  1. Chapter 14 Equilibrium Suroviec Spring 2014

  2. I. Equilibrium • So far we have mostly considered just forward reactions aA + bB  cC + dD • But all reactions can move in either direction

  3. A. State of equilibrium • Rate of equilibrium • Equilibrium is dynamic

  4. B. Positions of equilibrium

  5. II. Equilibrium Constant • Omit concentrations of pure solids and liquids because those concentrations will not change • Look at elementary steps:

  6. A. What does K mean? • Large value of K means product favored 2. Small value of K means reactant favored

  7. III. Reaction Quotient

  8. Example Given the K of this reaction to be 170, when the conditions are changed what is the Q? Given the new Q, what is the direction of the reaction to re-establish equilibrium?

  9. IV. Calculations with K • We need the equilibrium concentrations to determine K, be we usually know initial concentrations, we can therefore get there from the balanced chemical equations!!! • Butane interconverts to isobutane at 25oC with a K = 2.5. If 0.017 moel of butane is in 50 mL, what is the concentration of both species at equilibrium?

  10. Example PCl5 (g) PCl3 (g) + Cl2 (g) K is 1.2 at 25oC. If you place 0.300 M PCl5 (g) in a flask what are the equilibrium concentrations of PCl3 (g), PCl3 (g) and Cl2 (g)?

  11. Example H2 (g) + Br2(g) 2HBr (g) • K is 2.18 × 106 at 730oC. If you place 0.267 M HBr (g) in a flask and allow it to come to equilibrium, what are the equilibrium concentrations of H2 (g), Br2 (g) and HBr (g)?

  12. V. Manipulating Equilibrium Expressions N2(g) + 3H2 (g) 2NH3 (g) 2N2(g) + 6H2 (g) 4NH3 (g)

  13. Rules for Manipulating When the stoichiometric coefficients in a balanced reaction are changed by a factor of n: • When a chemical reaction is reversed in • direction: • When several balanced reactions (each with its own equilibrium constant) are added to obtain a net balanced equation:

  14. Ex Calculation Knet for the following reaction: Fe (s) + H2O (g) FeO (s) + H2 (g) Given the following information: H2O (g) + CO (g) H2 (g) + CO2 (g) K1 = 1.6 FeO (s) + CO (g) Fe (g) + CO2 (g) K2 = 0.67

  15. VI. LeChatelier’s Principle • Any change in any of the factors that determine the equilibrium conditions of a system will cause the system to change in such a manner to counteract the effect of the change • Systems always want to be at equilibrium and will work to get back there.

  16. Example 2SO2 (g) + O2 (g) 2SO3(g) ΔHrxn = -197 kJ Disturbances: • Add more SO2(g) • Take away O2 (g) • Decrease the volume by ½

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