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CHEMICAL EQUILIBRIUM Chapter 16

CHEMICAL EQUILIBRIUM Chapter 16. “Systems”: two reactions that differ only in direction. Any reversible reaction. H 2 + I 2 ↔ 2HI. noted by the double arrow; ↔. TWO REACTIONS. only difference is the Direction. H 2 + I 2 ↔ 2HI. reactants. products. 2HI ↔ H 2 + I 2. Left. Right.

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CHEMICAL EQUILIBRIUM Chapter 16

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  1. CHEMICAL EQUILIBRIUMChapter 16

  2. “Systems”: two reactions that differ only in direction • Any reversible reaction H2 + I2↔ 2HI noted by the double arrow; ↔

  3. TWO REACTIONS • only difference is the Direction H2 + I2↔ 2HI reactants products 2HI ↔ H2 + I2 Left Right

  4. Reversible Reactions H2 + I2 ↔ 2HI • the products may react back to original reactants. • “closed system”: ONLY if all reactant are present • If one piece is completely gone it has ”gone to competition” and no longer reversible

  5. Examples: Reversible Reactions. • Unopened Soda • Breathing • Rechargeable batteries • Color changing shirt

  6. Equilibrium • The state in which a chemical reaction and its reverse reaction occur at the same rate.

  7. Equilibrium = No change in amount over time

  8. Properties of an Equilibrium Equilibrium systems are • DYNAMIC (in constant motion) • REVERSIBLE • can be approached from either direction Pink to blue Co(H2O)6Cl2 ---> Co(H2O)4Cl2 + 2 H2O Blue to pink Co(H2O)4Cl2+ 2 H2O ---> Co(H2O)6Cl2

  9. Equilibrium Rates = 0 No change in the amounts

  10. Equilibrium achieved Reversible Reactions Product conc. increases and then becomes constant at equilibrium Reactant conc. declines and then becomes constant at equilibrium

  11. Chemical Equilibrium Fe3+ + SCN-aFeSCN2+ At Equilibrium: RATES ARE EQUAL • the concentrations of reactants and products are constant. D [ ]’s = 0 • The forward and reverse reactions continue after equilibrium is attained.

  12. Reaction Quotient At anypointin the reaction H2 + I2 --->2 HI

  13. The Reacton Quotient, Q In general, all reacting chemical systems are characterized by their REACTION QUOTIENT, Q. When the system is at equilibrium, Q = K

  14. Equilibrium achieved Equilibrium Constant In the equilibrium region

  15. THE EQUILIBRIUM CONSTANT For any type of chemical equilibrium of the type aA + bB--->cC + dD the following is a CONSTANT (at a given T) If K is known, then we can predict concs. of products or reactants.

  16. Writing and Manipulating K Expressions Solids NEVER appear in equilibrium expressions. S(s) + O2(g) ---> SO2(g)

  17. Writing and Manipulating K Expressions Liquids NEVER appear in equilibrium expressions. NH3(aq) + H2O(liq) ---> NH4+(aq) + OH-(aq)

  18. Writing Equilibrium Expressions

  19. Product- or Reactant Favored Product-favored Reactant-favored

  20. For: N2(g) + 3 H2(g) ---> 2 NH3(g) Using K: Is the reaction product-favored or reactant-favored? When K is much greater than 1 the reaction is strongly product-favored.

  21. For AgCl(s) g Ag+(aq) + Cl-(aq) Kc = [Ag+] [Cl-] = 1.8 x 10-5 If K is much less than 1 The reaction is strongly reactant-favored. Ag+(aq) + Cl-(aq) gAgCl(s) is product-favored.

  22. Using K: Can determine if the reaction is at equilibrium.

  23. If [iso] = 0.35 M and [n] = 0.15 M, are you at equilibrium? If not, which way does the reaction “shift” to approach equilibrium?

  24. REACTION QUOTIENT, Q Characterize all chemical systems If Q = K, then system is at equilibrium. Q (2.33) < K (2.5) Reaction is NOT at equilibrium, [iso] must ________ and [n] must ____________.

  25. Experimental Determination of Equilibrium Constant, K 2 NOCl(g) --->2 NO(g) + Cl2(g) Place 2.00 mol of NOCl is a 1.00 L flask. At equilibrium you find 0.66 mol/L of NO. Calculate K. Set of an “ICE” table of concentrations [NOCl] [NO] [Cl2] Initial 2.00 0 0 Change Equilibrium 0.66

  26. Determining K 2 NOCl(g) ---> 2 NO(g) + Cl2(g) [NOCl] [NO] [Cl2] Initial 2.00 0 0 Change -0.66 +0.66 +0.33 Equilibrium 1.34 0.66 0.33

  27. 2 NOCl(g) ---> 2 NO(g) + Cl2(g) [NOCl] [NO] [Cl2] Initial 2.00 0 0 Change -0.66 +0.66 +0.33 Equilibrium 1.34 0.66 0.33

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