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Reaction Equilibrium

Reaction Equilibrium. Unit 17 Daily 2. Key Question:. What is Le Chatelier’s Principle?. Today’s Goals:. Explore factors affecting equilibrium Predict direction of equilibrium shift Predict resulting changes in concentration Make equilibrium serve your own evil purposes.

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Reaction Equilibrium

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  1. Reaction Equilibrium Unit 17 Daily 2

  2. Key Question: What is Le Chatelier’s Principle?

  3. Today’s Goals: • Explore factors affecting equilibrium • Predict direction of equilibrium shift • Predict resulting changes in concentration • Make equilibrium serve your own evil purposes

  4. Factors Affecting Equilibrium • Equilibrium is a RATE balance. • Anything that can affect the rate of the forward or reverse reaction can throw equilibrium off. • What are the factors that affect reaction rate? • Concentration • Pressure or Volume (gases) • Temperature • Surface Area • Catalysts/Inhibitors

  5. Le Chatelier’s Principle • “If a system at equilibrium is subjected to an external stress, the equilibrium will shift to minimize the effects of that stress” • The Steps of Le Chatelier’s Principle: • Stress: Adding or removing a reactant, adding or removing a product, changing the pressure, volume, or temperature. • Shift: The equilibrium will shift away from what is added and towards what is removed. • Change in Concentration: The concentration of what is being shifted towards increases, the concentration of what is being shifted away from decreases.

  6. Changes in Concentration Fe3+(aq) + SCN-(aq) FeSCN2+(aq) (colorless) (red) If more Fe3+ is added to the system, what will happen? • equilibrium shifts to the right • equilibrium shifts to the product side • the forward reaction is favored (forward shift) How are concentrations affected? • [Fe3+] increases, [SCN-] decreases, [FeSCN2+] increases How is Keq affected? • Keq does not change when changes in concentration cause a shift in equilibrium

  7. Changes in Concentration Fe3+(aq) + SCN-(aq) FeSCN2+(aq) (colorless) (red) If more FeSCN2+ is added to the system, what will happen? • equilibrium shifts to the left • equilibrium shifts to the reactant side • the reverse reaction is favored (reverse shift) How are concentrations affected? • [Fe3+] increases, [SCN-] increases, [FeSCN2+] increases

  8. Changes in Concentration Fe3+(aq) + SCN-(aq) FeSCN2+(aq) (colorless) (red) If SCN- is removed from the system (by adding AgNO3 so that AgSCN(s) precipitate forms), what will happen? • equilibrium shifts to the left • equilibrium shifts to the reactant side • the reverse reaction is favored (reverse shift) How are concentrations affected? • [Fe3+] increases, [SCN-] increases (but also decreases since it was removed), [FeSCN2+] decreases

  9. Changes in Volume & Pressure • Only affect an equilibrium system if gases are present • What is the relationship between moles of gas and volume/pressure? • P = (nRT)/(V) • If pressure is increased (or volume decreased): • equilibrium will shift towards the side with FEWER moles of gas to bring the pressure back down • If pressure is decreased (or volume increased): • equilibrium will shift towards the side with MORE moles of gas to bring the pressure back up

  10. Changes in Volume & Pressure N2(g) + 3H2(g) 2NH3(g) (4 moles) (2 moles) If pressure is increased (volume decreased) on the system, what will happen? • equilibrium shifts to the right • equilibrium shifts to the product side • the forward reaction is favored (forward shift) How are concentrations affected? • [N2] decreases, [H2] decreases, [NH3] increases

  11. Changes in Volume & Pressure Notes: • If the number of moles of gas are equal on both sides, then the equilibrium can’t shift H2(g) + I2(g) 2HI(g) • Make sure to only count the moles of GAS when considering pressure effects on equilibrium

  12. Changes in Temperature If temperature is increased in the system, what will happen? • equilibrium will shift in the endothermic direction • the endothermic direction is away from the side with heat If temperature is decreased in the system, what will happen? • equilibrium will shift in the exothermic direction • the exothermic direction is towards the side with heat

  13. For Those Who Prefer Visuals…

  14. See Saw H2O H OH

  15. Add More Hydrogen H2O H H OH Which way does the see saw have to shift to reach equilibrium again?

  16. Add More Hydrogen H2O H H OH Which way does the see saw have to shift to reach equilibrium again?

  17. Add More Hydrogen SHIFT LEFT H H2O H OH More H2O is produced due to the shift in equilibrium

  18. Synthesis of Ammonia H2 H2 NH3 NH3 N2 H2 N2 (g) + 3H2 (g)  2NH3 (g)

  19. Increase Pressure SHIFT RIGHT NH3 NH3 H2 H2 H2 N2 SHIFT will occur to side with the least number of MOLES N2 (g) + 3H2 (g)  2NH3 (g)

  20. Decreasing Volume(Think about how P and V relate with Boyle’s Law) H2 H2 NH3 NH3 N2 H2 N2 (g) + 3H2 (g)  2NH3 (g)

  21. Decrease Volume = Increase Pressure SHIFT RIGHT NH3 NH3 H2 H2 H2 N2 SHIFT will occur to side with the least number of MOLES N2 (g) + 3H2 (g)  2NH3 (g)

  22. Change in Temperature • Depends if reaction is Endothermic or Exothermic. • Endothermic: Heat on LEFT • Exothermic: Heat on RIGHT

  23. Exothermic • Increase Temperature… which way will the see saw tip? HEAT D A C B

  24. Exothermic Which way will the reaction shift? A HEAT B C D

  25. Exothermic Reaction will SHIFT LEFT A HEAT B C D

  26. Exothermic DecreaseTemperature… which way will the see saw tip? HEAT D A C B

  27. Exothermic Which way will the reaction shift? HEAT D C B A

  28. Exothermic Reaction will SHIFT Right HEAT D C B A

  29. Endothermic • Increase Temperature… which way will the see saw tip? HEAT D A C B

  30. Endothermic • Which way will the reaction SHIFT? HEAT D C B A

  31. Endothermic • Reaction will SHIFT Right HEAT D C B A

  32. Endothermic • Decrease Temperature… which way will the see saw tip? HEAT D A C B

  33. Endothermic • Which way will the reaction SHIFT? HEAT A B C D

  34. Endothermic • Reaction will SHIFT Left HEAT A B C D

  35. Demo: Changes in Temperature 2NO2(g) N2O4(g) + energy (Dark Brown) (Clear)

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