1. Kinetics
Unit E
Lundquist 2017

2. Collision Theory & Instantaneous Rate Law
Unit E.1

3. Video Time

4. Collision Theory
Reactions only occur if reactants collide with enough energy & in the correct orientation

5. Reaction Rates
Rate = change in concentration of a reactant or product per unit time
𝑀 𝑠 -or- 𝑚𝑜𝑙 𝐿×𝑠
determined experimentally
Appearance of Prod
Concentration of rxts
Change in temp.

6. Factors that effect reaction rates
Notes
p. 1
Factors that effect reaction rates
GENERALLY: 10oC increase doubles speed
Nature of Reactants
Concentrations
Surface Area
Temperature
Catalysts

7. Tricky Tricky
Adding an inert gas DOES NOT affect the rate of a reaction!
Inert means unreactive
Usually Ar / He (noble gases)

8. Unit E.1 Note Quiz Questions1. 3. 2. 4.

9. Collision Theory
Reactions only occur if reactants collide with enough energy & in the correct orientation

10. Remember
Activation energy (Ea) is the amount of energy rxts need when they collide to produce collisions
“Fruitful collisions”
DH = prod – rxts
+DH = endothermic
-DH = exothermic

11. Unit E.1 Note Quiz Questions5. 6. 7.

12. Maxwell-Boltzmann Distributions
Area under the curve represents the number of collisions with Ea marked

13. Maxwell-Boltzmann Distributions
Which temperature is higher?
T2 because more collisions are fruitful (have enough energy to overcome activation energy)

14. Chemical Reaction Rates
The speed of the reaction
𝑅𝑎𝑡𝑒 =− ∆ 𝑟𝑛𝑡 ∆𝑡 𝑜𝑟 ∆ 𝑝𝑟𝑜𝑑 ∆𝑡
Changes with time

15. Instantaneous Reaction Rate
The rate at a given time
Determined by finding the tangent of the curve

16. Instantaneous Reaction Rate (practice)
What is the reaction rate for the reactants at 10s and at 20s?
What is the reaction rate for the products at 10s and at 20s?

17. Relative Reaction Rate
How rates relate to each other in a chemical reaction
Reactants are used up (-rate)
Products are produced (+rate)
Look to the stoichiometry
Put a 1 over the coefficient
Can remove the fraction by multiplying by the common denominator
2𝑁 𝑂 2 𝑔 → 𝑂 2 𝑔 +2𝑁𝑂(𝑔)
𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝑟𝑎𝑡𝑒 =− ∆[𝑁 𝑂 2 ] ∆𝑡 =+ ∆[ 𝑂 2 ] ∆𝑡 = ∆[𝑁𝑂] ∆𝑡
-or-
Initial rate = -1:+2:+1

18. Practice
What is the initial relative reaction rate for the following reactions? What is the whole number ratio? 4 𝑃 𝐻 3 → 𝑃 4 +6 𝐻 2 𝑅𝑎𝑡𝑒=− 1 4 ∆[𝑃 𝐻 3 ] ∆𝑡 =+ ∆[ 𝑃 4 ] ∆𝑡 =+ 1 6 ∆[ 𝐻 2 ] ∆𝑡 -Or- Rate = -3 : 12 : 2

19. Unit E.1 Note Quiz Questions8. 10 9.

20. Differential Rate Law
Unit E.2

21. Differential Rate Law Rate Expression
Equilibrium
When the ratefwd = ratervs
Would GREATLY complicate this SOOOO…
We will focus ONLY on rates immediately after mixing
How to measure rate:
Count bubbles
Mass precipitate
Spectroscopy (how we’re doing this lab)

22. Differential Rate Law Rate Expression
𝑎𝐴+𝑏𝐵 →𝑥𝑋
Rate Law written as:
𝑅𝑎𝑡𝑒=𝑘 𝐴 𝑚 𝐵 𝑛
k = rate constant
[A] = concentration of reactant A
[B] = concentration of reactant B
m = order of reaction for reactant A
n = order of reaction for reactant B
Can be zero, whole numbers, or fractions. CAN ONLY BE DETERMINED BY EXPERIMENTATION

23. Differential Rate Law Rate Expression
The Rate Constant (k)
LOWER CASE k
Temperature dependent
Units are needed to make 𝑟𝑎𝑡𝑒= 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 𝑡𝑖𝑚𝑒 = 𝑚𝑜𝑙 𝐿 × 𝑠𝑒𝑐
What would be the units of K for:
Rate = k[A]1
𝑀 𝑠𝑒𝑐 = 𝑋 𝑌 𝑀

24. Differential Rate Law Rate Expression
Orders
Can only be determined by looking at concentration and rate data
Overall order is the sum of the exponents
Rates

25. Differential Rate Law Rate Expression
𝑟𝑎𝑡𝑒=𝑘 [𝐴] 0
Zero Order
Changing the concentration of the reactant does not change the rate of the reaction
Unusual but possible
Easiest to spot
m = 0
rate = k

26. Differential Rate Law Rate Expression
𝑟𝑎𝑡𝑒=𝑘 [𝐴] 1
First Order
doubling the concentration of the reactant does doubles the rate of the reaction
VERY common (ex: nuclear decay)
m = 1

27. Differential Rate Law Rate Expression
𝑟𝑎𝑡𝑒=𝑘 [𝐴] 2
Second Order
doubling the concentration of the reactant does quadruples the rate of the reaction
common for gases
m = 2

28. Differential Rate Law Two ways to determine from data
Table logic
Ugly Algebra
Faster
Requires you to KNOW definitions
May require you to make assumptions (can be wrong )
MUCH slower
Never fails
Can be a bit confusing

29. 𝐴+𝐵 →𝑃𝑟𝑜𝑑𝑢𝑐𝑡 Determine the rate expression

30. 𝐴+𝐵 →𝑃𝑟𝑜𝑑𝑢𝑐𝑡 Determine the rate constant (k)
Rate = k[B]
Use any experiment to find k
Units of k
Overall order -1 is the molarity (M)
1 𝑀 𝑜𝑣𝑒𝑟𝑎𝑙𝑙−1 × 𝑡𝑖𝑚𝑒

31. Practice

32. Practice

33. Unit E.2 Note Quiz Questions1

34. Unit E.2 Note Quiz Questions4 3

35. Unit E.2 Note Quiz Questions5

36. Do p.

37. Reaction Mechanisms series of reactions that result in the goal reaction (like hess’ law)
Rules:
Must be done experimentally (meaning I will give them to you)
Must agree with the stoichiometry
Must agree with the rate law

38. Reaction Mechanisms describing mechanisms
Elementary step – a proposed step in the over all reaction
Molecularity – number of molecules that participate the the step

39. Practice

40. Rate determining step
The rate of the reaction is limited by the combined rates up to the SLOWEST step
In the reaction 2𝑋+𝑌 → Z For a particular reaction the rate is found to be 𝑟𝑎𝑡𝑒=𝑘[𝑌] Which of the below purposed mechanisms is a valid mechanism for this reaction?

41. Quiz Next Class Determine the order of the reaction for each reactant
Determine the over all order
Use stoich. or the rate law to find the concentration at a set time
Justify a mechanism and identify the slow step.

42. Integrated Rate Law
Unit E.3

43. Rate Laws Differential Rate Law Integrated Rate Law
Concentration vs rate data
Use table logic or ugly algebra to find rate law & value of K
Concentration vs time data
Must choose the straightest line graph and know what it means
ONLY one reactant
k is the |slope|

44. Orders by integrated rate law (alphabetize concentration, natural log, and reciprocal)
𝑘=−𝑚
𝑘=−𝑚
𝑘=𝑚

45. Zero Order If [A] : time has an (𝑟 𝑣𝑎𝑙𝑢𝑒 ) 2 ≈1 then zero order so:
𝑦 = 𝑚 𝑥 𝑏
𝐴 =−𝑘 𝑡𝑖𝑚𝑒 +[ 𝐴 𝑖 ]

46. First Order
If ln[A] : time has an (𝑟 𝑣𝑎𝑙𝑢𝑒 ) 2 ≈1 then first order so:
𝑦 = 𝑚 𝑥 𝑏
𝑙𝑛 𝐴 =−𝑘 𝑡𝑖𝑚𝑒 +𝑙𝑛[ 𝐴 𝑖 ]

47. Second Order
If 1 [𝐴] : time has an (𝑟 𝑣𝑎𝑙𝑢𝑒 ) 2 ≈1 then Second order so:
𝑦 = 𝑚 𝑥 𝑏
1 𝐴 =𝑘 𝑡𝑖𝑚𝑒 + 1 [ 𝐴 𝑖 ]

48. Unit E.3 Note Quiz Questions1

49. Unit E.3 Note Quiz Questions

50. Practice
Finish PE.2

51. Kinetics Clean Up
Unit E.4

52. Half Life With respect to kinetics
Just need to be able to
Discuss order (what order is it NOT)
Determine half life
What is the concentration after a set number of half lives
What time would a set concentration be found

53. Half Life Practice What order is it NOT? Determine half life
What is the concentration after the second half life?
When would 75% of the sample have decayed?

54. Unit E.5 Note Quiz Questions1 2 3

55. Swamping Integrated rate law with more than 1 reactant
We maximize one reactants concentration so that ANY change is negligible
What we will do in lab

56. Do number 1a on p.

57. Reaction Mechanisms series of reactions that result in the goal reaction (like hess’ law)
Rules:
Must be done experimentally (meaning I will give them to you)
Must agree with the stoichiometry
Must agree with the rate law

58. Reaction Mechanisms describing mechanisms
Elementary step – a proposed step in the over all reaction
Molecularity – number of molecules that participate the the step

59. Unit E.5 Note Quiz Questions4

60. Practice

61. Rate determining step number 1b on p.
The rate of the reaction is limited by the combined rates up to the SLOWEST step
In the reaction 2𝑋+𝑌 → Z For a particular reaction the rate is found to be 𝑟𝑎𝑡𝑒=𝑘[𝑌] Which of the below purposed mechanisms is a valid mechanism for this reaction?

62. Unit E.5 Note Quiz Questions7 6 5

63. Practice

64. Do p.

65. Catalysts NOT CONSUMED Lower activation energy DON’T change DH
Homogeneous catalyst – same phase
Heterogeneous catalyst – different phase

66. Unit E.5 Note Quiz Questions8 10 9

67. Test Next Class
30 Multiple choice
45 minutes
4 free response