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Reaction Rates and Le Chatelier’s Principle

Reaction Rates and Le Chatelier’s Principle. Rate of Reaction. The rate of a chemical reaction Describes how rapidly a chemical change takes place They are determined by measuring changes in physical properties Volume, Temperature, Color, Mass, or pH. Five Factors that Affect Reaction Rate.

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Reaction Rates and Le Chatelier’s Principle

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  1. Reaction Rates and Le Chatelier’s Principle

  2. Rate of Reaction • The rate of a chemical reaction • Describes how rapidly a chemical change takes place • They are determined by measuring changes in physical properties • Volume, Temperature, Color, Mass, or pH

  3. Five Factors that Affect Reaction Rate • 1. Nature of the reactants • 2. Temperature • 3. Concentration • 4. Surface Area • 5. Catalysts

  4. Chemical Equilibrium • At equilibrium the forward reaction and the reverse reaction happen at the same time • There is no change in the amount of any substance in the reaction • Le Chatelier’s principle can be used to predict the effect of a change in conditions on a chemical equilibrium

  5. Le Chatelier’s Principle Summarized • If a chemical system at equilibrium experiences a change (also called a stress) in concentration, temperature, volume, or total pressure; the equilibrium will shift in order to minimize that change.

  6. See Saw A B C

  7. Add More B A B B C Which way does the see saw have to shift to reach equilibrium again?

  8. The Shift A B B C Which way does the see saw have to shift to reach equilibrium again?

  9. Results SHIFT LEFT B A B C More A is produced due to the shift in equilibrium

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

  11. 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)

  12. 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)

  13. Decrease Volume 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)

  14. P and V • P and V are inversely related. That means as P increases, then V decreases. • The rule is when P increases or V decreases then the equilibrium will shift to the side with the least number of moles. • This only works if all of the components are gasses.

  15. 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)

  16. Change in Temperature • Depends if reaction is Endothermic or Exothermic. • Endothermic: Heat on LEFT (+) • Exothermic: Heat on RIGHT (-)

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

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

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

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

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

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

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

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

  29. How does each situation affect the chemical reaction? CauseEffect 2H2O  2H2 + O2

  30. Which INCREASE Reaction Rates? • Increasing Temperature • Increasing Concentration • Increasing Surface Area • Adding a Catalyst. • How are these factors related to Reaction Rates? • DIRECTLY

  31. Nature of Reactants • Reaction rates are affected by the complexity of the bonds that must be broken and formed in the chemical reaction • The state of a reactant can also affect the reaction rate • Gases have the fastest and solids the slowest reaction rats • Because the frequency at which particles collide and the amount of energy they possess increase with increasing motion.

  32. Continued • The faster particles are moving, the more frequent they will collide • Collide with greater kinetic energy. • Because of this TEMPERATURE and REACTION RATE are directly related

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