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Chemical Kinetics or Reaction Rates

Chemical Kinetics or Reaction Rates. You have 6 ball bearings with identical magnetic strength but different diameters where A > B > C > D > E > K. Which two will hold together the most & the least. Reaction Rate. The speed at which reactants become products in a chemical reaction M/s.

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Chemical Kinetics or Reaction Rates

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  1. Chemical Kinetics or Reaction Rates

  2. You have 6 ball bearings with identical magnetic strength but different diameters where A > B > C > D > E > K. Which two will hold together the most & the least.

  3. Reaction Rate • The speed at which reactants become products in a chemical reaction • M/s

  4. Kinetic Theory • All matter is made up of tiny particles • The particles are in constant motion • All collisions are elastic ?

  5. Elastic Collisions • Collisions in which there is no energy change

  6. Particles Reacting • For particles to react, they must collide • Reaction rate is dependent on collision rate

  7. Particles Reacting • When a reaction takes place, an energy change occurs • Collision in which reactions occur are not elastic

  8. Reaction Rate • Rate = - d[Reactant]/dt • Rate = +d[Product]/dt • M/s

  9. Factors Affecting Rxn Rate • Concentration, Temperature, Agitation, Process, Orientation, Catalyst, SA of Solid, Pressure of Gas, Reaction Mechanism

  10. List & describe all of the factors affecting rxn rates.

  11. Drill: • List at least 5 factors that will affect reaction rates

  12. Rate Expression • An equation showing how rate depends on the amount of reactants in a rate determining reaction

  13. Rate Expression • Rxn: aA(aq) + bB(aq) P • Expr: Rate = k[A]a[B]b • [A] = molarity of A

  14. Rate Expression • Rxn: aA(g) + bB(g) Product • Exp: Rate = kPAaPBb

  15. Write Rate Expressions for: H2(g) + N2(g) NH3(g) HCl(aq) + Ba(OH)2(aq) BaCl2(aq) + H2O (l)

  16. Write Rate Expressions for: Cl2(g) + HOOH (aq) P(aq)

  17. Reaction Order • The total number of reactants • Equals total of all of the coeffecients of R in the rxn • Equals total exponents in rate expression

  18. Determining Rxn Rate • Find rate expression ratios • (Ratio of concentrations)x = rate ratio • x = exponent

  19. Experimental Results Exp [A] [B] [C] Rate 1 1.0 1.0 1.0 2 2 2.0 1.0 1.0 4 3 1.0 2.0 1.0 8 4 1.0 1.0 2.0 4

  20. Experimental Results Exp # [A] [B] [C] Rate 1 0.1 0.1 0.1 3 2 0.3 0.1 0.1 9 3 0.1 0.3 0.1 27 4 0.1 0.1 0.3 3

  21. Half-Life • The time required for one half of a reactant to be decomposed in a reaction

  22. Useful Relationships Rxn Order Rate Exp 0 R=k 1 R=k[A] 2 R=k[A]2

  23. Useful Relationships Rxn Order Half Life 0 [Ao]/2k 1 0.693/k 2 1/k[A]

  24. Useful Relationships Rxn Order Lin Plot 0 [A] vs k 1 ln[A] vs k 2 1/[A] vs k

  25. Useful Relationships • Rxn Order Calc R E • 0 -d[A]/dt = k • 1 -d[A]/dt = k[A] • 2 -d[A]/dt = k[A]2

  26. Experimental Results Exp # [R] [S] [T] Rate 1) 0.25 0.20 0.10 2 2) 0.25 0.60 0.10 18 3) 0.50 0.20 0.10 4 4) 0.25 0.20 0.40 32

  27. Clausius-Claperon Eq (T2)(T1) k2 (T2 – T1) k1 Ea= R ln

  28. Calculate the activation energy of a reaction whose rate constant is 2.0 x 103 at 27oC and is 2.0 x 106 at 77oC:

  29. Experimental Results Exp # T [A] [B] Rate 1) 27oC 0.10 0.10 2 2) 27oC 0.30 0.10 18 3) 27oC 0.10 0.20 4 4) 77oC 0.10 0.10 20

  30. Reaction Mechanism • The sequence of steps that make up the reaction process

  31. Reaction Mechanism Step 1 A <--> B fast Step 2 B ---> C slow Step 3 C <--> D fast Total A ---> D

  32. Reaction Mechanism • The rate determining step in a reaction mechanism is the slowest step

  33. Reaction Mechanism • To solve the rate expression, you must use the slowest step

  34. Solve Rate Expression A + B C + D fast 2C + A G fast 2D + B K fast 2G + 2K Prod. slow

  35. Solve Rate Expression X + Y M + N fast M + N 2G slow 2N + G K fast 2G + 2K Prod. fast

  36. Solve Rate Expression X + Y M + N fast 3M + N 2G fast 2N K fast 4G + 2K Prod. slow

  37. Solve Rate Expression A + B C + D fast 4C + A 2G fast 4D + B 2K fast G + K Q + W slow Q + W Prod. fast

  38. Review

  39. Experimental Results Exp # T [A] [B] Rate 1) 27oC 0.10 0.10 2 2) 27oC 0.30 0.10 18 3) 27oC 0.10 0.20 8 4) 77oC 0.10 0.10 20

  40. Solve Rate Expression A + B C + D fast 4 C + A 2G fast 2 K 4D + B fast G + K Q + W fast 2Q + 2W Prod. slow

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