Tang 03 rate theories

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Tang 03 rate theories

  1. 1. RATE THEORIES
  2. 2. RATE THEORIES <ul><li>Collision Theory </li></ul><ul><li>Transition State Theory </li></ul><ul><li>Catalysts </li></ul>
  3. 3. RATE THEORIES COLLISION THEORY: The rate of rxn is proportional to the number of effective/successful collisions per second between reactant molecules. What factors determine whether reactants could form a molecule? (e.g. is bumping into each other enough?)
  4. 4. Not all collisions are effective. Effective collision: A collision that actually results in the production of product molecules In a game of pool, what are the two conditions that are required for an effective collision? RATE THEORIES COLLISION THEORY:
  5. 5. WRONG ORIENTATION RATE THEORIES COLLISION THEORY: Not all collisions are effective 8 3
  6. 6. CORRECT ORIENTATION! RATE THEORIES COLLISION THEORY: 3 8
  7. 7. INCORRECT SPEED! RATE THEORIES COLLISION THEORY: Not all collisions are effective 3 8
  8. 8. CORRECT SPEED!!! RATE THEORIES COLLISION THEORY: 3 8
  9. 9. RATE THEORIES <ul><li>COLLISION THEORY: </li></ul><ul><li>For a collision to be effective, the molecules must collide with the proper: </li></ul><ul><ul><li>orientation </li></ul></ul><ul><ul><li>kinetic energy </li></ul></ul>8 SCORE
  10. 10. RATE THEORIES <ul><li>Orientation : H 2 + I 2  2 Hl </li></ul>COLLISION THEORY:
  11. 11. RATE THEORIES <ul><li>Orientation : NO + NO 3  2 NO 2 </li></ul>COLLISION THEORY:
  12. 12. RATE THEORIES <ul><li>Kinetic energy : A minimum kinetic energy, called activation energy (E a ), is required between reactants for a reaction to proceed. </li></ul><ul><ul><li>E a is unique to each reaction </li></ul></ul><ul><li>Higher temperatures result in a higher percentage of reactants with enough energy to react. </li></ul>COLLISION THEORY:
  13. 13. RATE THEORIES <ul><li>Kinetic energy : </li></ul>COLLISION THEORY:
  14. 14. RATE THEORIES <ul><li>Kinetic energy : </li></ul>COLLISION THEORY: number of particles energy Only a fraction of the reactant molecules collide with enough kinetic energy
  15. 15. RATE THEORIES COLLISION THEORY: <ul><li>Factors affecting effective collisions: </li></ul><ul><ul><li>molecule orientation </li></ul></ul><ul><ul><li>molecule energy </li></ul></ul><ul><li>Collision Theory Animation </li></ul><ul><li>Collision Theory Applet </li></ul>
  16. 16. RATE THEORIES TRANSITION STATE THEORY: Potential energy Reaction coordinate Potential energy diagrams Reactants Products E a Δ H The transition state complex (or activated complex) is formed at this peak
  17. 17. RATE THEORIES TRANSITION STATE THEORY: Potential energy diagrams The transition state complex (bonds break and form at the same time) Potential energy Reaction coordinate Reactants Products E a Δ H
  18. 18. RATE THEORIES TRANSITION STATE THEORY: Potential energy diagrams
  19. 19. RATE THEORIES TRANSITION STATE THEORY: Potential energy Reaction coordinate Draw the potential energy diagram for the reverse reaction Reactants Products E a Δ H
  20. 20. RATE THEORIES TRANSITION STATE THEORY: Examine the E a for both reactions. What does that suggest? E a is different between the forward and reverse directions of a given reaction. Generally, endothermic reactions are slower than exothermic reactions due to a higher E a .
  21. 21. RATE THEORIES TRANSITION STATE THEORY: <ul><li>Identify E a ,  H and transition state. </li></ul><ul><li>What are the values of E a and  H? 50kJ, -100kJ </li></ul><ul><li>Endothermic or exothermic? Exothermic </li></ul><ul><li>What are E a and  H for the reverse rxn? 150kJ, 100kJ </li></ul>
  22. 22. RATE THEORIES CATALYST: catalyst - a substance that increases the rate of a chemical reaction without being consumed homogeneous catalyst - exist in the same phase as the reactants heterogeneous catalyst - exist in a different phase as the reactants
  23. 23. RATE THEORIES CATALYST: Catalysts lower the E a of a reaction
  24. 24. RATE THEORIES CATALYST: Catalysts lower the E a of a reaction
  25. 25. RATE THEORIES CATALYST: <ul><li>Catalysts: </li></ul><ul><li>bend or stretch bonds to make them easier to break / react </li></ul><ul><li>reduce E A (make transition state easier) </li></ul><ul><li>bring two reactants close together </li></ul><ul><li>provide a microenvironment for reactions </li></ul>
  26. 26. RATE THEORIES CATALYST: Inhibitors - bind with the reactant or the catalyst to prevent the reaction from occurring and reducing reaction rate

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