1. Chemical Kinetics Chapter 16

2. Kinetics Reaction Rates Factors affecting rate Quantitative rate expressions DeterminationFactors Models for Rates Reaction Mechanisms Effects of catalysts

3. Rates Change in concentration of a reactant or product per unit time

6. Factors affecting rates Nature of the reactants State of subdivision/surface area ConcentrationTemperatureCatalysts

7. Reactants Complexity Bond strengths Etc.

15. Concentrations as functions of time

16. Graph: Concentration vs. time

17. Average Rate Change of concentration in a time interval

18. Average Rate Slope of line between two points on the graph

19. Instantaneous rate Slope of tangent line at a point on the graph

20. Instantaneous Rate 0.009 M 375 s

22. Initial Rate (t = 0)

23. Initial rate Slope of tangent line at time 0 (y intercept)

24. Rate Laws k =rate constant m, n =order rate =k[NO 2 ] n

25. Introduction to Rate Laws Reversible chemical reactions Forward:Backward:Equilibrium:

26. Introduction Dominant Reaction: Rate Law: k, k’:specific rate constant n :order of reactant n :order of reactant can be zero, fractional, or negative

27. Method of Initial Rates Unknown:k, m, n Initial rate:instantaneous rate just after reaction is initiated

28. Initial Rates, NO 2 decomposition

29. Order of Reaction General:Substituting:Solution:

30. Rate constant Rate 1 7.1 x 10 -5 M s -1 =-k[0.01 M] 2 k=0.71 M -1 s -1 Rate 2 2.8 x 10 -4 M s -1 =-k[0.02 M] 2 k=0.70 M -1 s -1

31. You try

32. O 2 + 2 NO  2NO 2

33. Overall Order Sum:1+2+3 =6 Overall order of reaction:6

34. Types Differential: Rate dependence on concentration Integrated: Concentration dependence on time

35. First Order Reactions For aA  products Differential:Integrated:

36. Half-life, first order reactions Integrated law: Half-life: Half of initial reacted [A] t = ½[A] 0 Independent of [A] 0

39. Second Order Reactions For aA  products Differential:Integrated:

40. Half-life, second order reactions Integrated law: Half-life: Half of initial reacted [A] t = ½[A] 0 Inversely proportional to [A] 0

41. Zero Order Reactions For aA  products Differential:Integrated:

43. Graphical Method First order Second order Zero order Straight line

44. First order Plot: ln[A] vs. time ln[A] time ln[A] 0 slope = -k

45. Second order Plot: 1 vs. time 1 vs. time [A] [A] time 1 [A] o slope = k 1 [A]

46. Zero order Plot: [A] vs. time [A] time [A] 0 slope = -k

49. Summary Conditions set so dominant forward reaction Differential Rate Laws rate as a function of concentration method of initial rates Integrated Rate Laws concentration as a function of time graphical method Experimental data collection Rate law types can be interconverted

50. Reaction Mechanism Chemical equation:Summary Mechanism:Series of elementary steps Elementary Steps:Reactions with rate laws from molecularity Molecularity:Number of species that must collide to produce reaction

52. Reaction Mechanism Proposed elementary steps must satisfy conditions: — reasonable reactions — sum of steps = overall balanced reaction — mechanism rate law = experimental rate law

53. Intermediates — appear in steps — produced in one step — used in subsequent — not in overall equation

54. Rate-determining step In a multi-step process: SLOWEST step Determines overall reaction rate “Bottleneck”

55. Model for Kinetics Collision Theory rate determined by particle collisions collision frequency and energy Transition State Theory how reactants convert to products

56. Collision Theory (Bimolecular Collsions) Z:no. of bimolecular collisions per second f a :fraction with E a P:fraction with correct orientation E a :activation energy

63. Arrhenius Equation k:rate constant E a :activation energy (minimum required) T:absolute temperature R:universal gas constant A:orientation factor Energy & orientation requirements for reaction

64. Hydrolysis of an ester

68. Transition State Theory E a and internal energy: Bonds breaking and forming Atoms rearranging “Transition State” Unstable intermediate At point of highest energy

69. forward reactionreverse reaction

70. exothermic reaction

72. I - + CH 3 Cl  Cl - + CH 3 I

78. Catalysts Speed reaction Are not consumed Alternative pathway for reaction with lower E a TypesHomogeneousHeterogeneous Enzymes are biological catalysts

82. Adsorption, activation, reaction, desorption