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Equilibrium

March 28, 2007. Equilibrium. Chemical Reactions. Reactants  Products A + 3B  2C But the reverse can also happen 2C  3B + A So we can describe the reaction as equilibrium A + 3B 2C. Forward Reaction. Reverse Reaction. Equilibrium.

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Equilibrium

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  1. March 28, 2007 Equilibrium

  2. Chemical Reactions Reactants  Products A + 3B  2C But the reverse can also happen 2C  3B + A So we can describe the reaction as equilibrium A + 3B 2C Forward Reaction Reverse Reaction

  3. Equilibrium rate of forward reaction = rate of reverse reaction

  4. Equilibrium - Concentration At equilibrium, the concentration of product and reactants stays constant

  5. Equilibrium Visualization http://www.dlt.ncssm.edu/TIGER/chem5.htm

  6. Law of Mass Action • Once a reaction has reached equilibrium, the relative concentration of products remains constant • We call this constant K, the equilibrium constant Example: N2 + 3H2 2NH3

  7. Equilibrium Expression • Things that appear in the equilibrium expression • Concentration of solutions • Pressure of gases • Reaction coefficient • Things that do NOT appear • Pure liquids • Pure solids • Units

  8. Learning Check Does this graph represent a K > 1, K< 1, or K =1 ? Greater number of reactants – K < 1

  9. Learning Check Determine the Equilibrium Expression (K) for each of the following reactions CaCO3(s) CaO (s) + CO2(g) 2NO2(g) N2O4(g) H2CO3(aq) CO2(g) + H2O(l)

  10. Calculating the Equilibrium Constant Calculate the equilbrium constant if the equilibrium concentrations of NO2 and N2O4 are 2.0 mol/L. 2NO2(g) N2O4(g)

  11. Equilibrium Position N2 (mol/L) H2 (mol/L) NH3 (mol/L) 30 30 900 10 40 800 5 45 675 • At constant temperature….reaction can only have one equilibrium constant but many equilibrium positions N2 + 3H2 2NH3 K = 640 (25 °C) • Equilibrium concentration of each product can be…

  12. Value of Equilibrium Constant A + 2B 2C + D • If K >>>>1, forward reaction is favored • Large concentration of products • If K <<<<1, reverse reaction predominates • Large concentration of reactants • If K = 1, reverse reaction and forward reaction equal • Equal concentration of reactants

  13. Changing the Equilibrium Constant • Change the temperature • Change the reaction coefficients • N2 + 3H2 2NH3 2N2 + 6H2 4NH3 Relationship between K1 and K2 K2 = K12 K2 = (640)2 = 4.096 x 105

  14. Changing the Equilibrium Constant • Change the temperature • Change the reaction coefficients • N2 + 3H2 2NH3 2NH3 N2 + 3H2 Relationship between K1 and K3 K3 = 1/K1K3 =1/ 640 = 0.00156

  15. Learning Check • Determine the value of the equilibrium constant for the following reaction • 2NO2 N2O4 ½ N2O4 NO2

  16. Disturbing the Equilibrium

  17. Heat as a Reactant/ Product • UO2(s) + 4HF(g)  UF4(g) + 2H2O(g

  18. FeSCN2+ Equilibrium • KSCN + Fe(NO3)3 FeSCN2+ + KNO3 • SCN- + Fe3+FeSCN2+ • Fe3+ + HPO42- FeHPO4+ • Ag+ + SCN- AgSCN • Ag+ + Cl- AgCl Spectator ions….ignore

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