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Topic 7 Equilibrium

Topic 7 Equilibrium. Dynamic equilibrium The position of equilibrium Equilibrium constants Le Chateliers principle Equilibrium in chemical processes. When A and B mixes the product C starts to form C reacts “back” to form A and B The reaction A +B  C and

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Topic 7 Equilibrium

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  1. Topic 7 Equilibrium • Dynamic equilibrium • The position of equilibrium • Equilibrium constants • Le Chateliers principle • Equilibrium in chemical processes

  2. When A and B mixes the product C starts to form • C reacts “back” to form A and B • The reaction A +B C and C A + B goes on at the same time • At equilibrium the rate for both reactions is the same • http://www.chm.davidson.edu/ronutt/che115/K/K_Solutions.htm

  3. 7.1 Dynamic equilibrium • Chemical equilibrium is a dynamic equilibrium. It may look like nothing is happening but reactions occur all the time. A + B C + D • means a reversible reaction, but sometimes ↔ or  is used

  4. In an equilibrium all of the species, A, B, C and D, is present. • Equilibrium doesn’t mean “equal”

  5. Physical equilibrium H2O(l) H2O(g)

  6. 7.2 Position of equilibrium A + B C + D Forward rate = kf[A][B] Reverse rate = kr[C][D] • At equilibrium: Forward rate = Reverse rate • kf/kr=Kc =[C][D] / [A][B] Kc:The Equilibrium constant Kc: temperature dependent

  7. a A + b Bc C + d DKc = [C]c[D]d / [A]a[B]b • H2 + I22 HI Kc= [HI]2 / [H2][ I2] • 4 NH3 + 5 O2 4 NO + 6 H2O Kc=[ H2O]6[NO]4 / [NH3]4[O2]5

  8. Units • Unit: Kc has not a fixed unit. Sometimes Kc can be without unit. • E.g. Kc =[ H2O]6[NO]4 / [NH3]4[O2]5 M6M4/M4M5= M

  9. When Kc >>1, the reaction goes almost to completion • When Kc<<1, the reaction hardly proceeds.

  10. Le Chatelier’sPrincipleChanges in Temperature, Pressure and Concentration will affect the equilibrium. A new equilibrium must be found.

  11. Observe that a catalyst doesn’t change the equilibrium but the equilibrium may be reached more rapidly.

  12. The Haber process N2(g) + 3 H2(g)2 NH3(g)DH = -92 kJ/mol With Iron catalyst. How to build an ammonia factory ?

  13. The Contact process 2SO2(g) + O2(g) 2SO3(g) DH= -196kJ/mol With V2O5 catalyst

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