1. Kinetics
Lesson 4
PE Diagrams

2. Potential Energy Diagrams Exothermic
Show the change in potential energy or enthalpy during a successful collision.
Standard Notation:
H2 + I2 → 2HI kJ
ΔH Notation:
H2 + I2 → 2HI ΔH = kJ
Both notations indicate an exothermic reaction. The first indicates that 170 KJ of KE are produced, while the second shows that the PE decreases by 170 KJ.
On the right
Or negative

3. Two reactants collide and form a complex species
Activated Complex
Two reactants collide and form a complex species

4. ΔH Forward/Enthalpy change
Exothermic Reaction ΔH= -

5. ΔH Reverse/Enthalpy change
Endothermic Reaction ΔH=+

6. Potential Energy Diagrams
Kinetic Energy (kJ)
Heat energy due to the motion of particles. Simulation
Potential Energy .
ΔH means change in enthalpy
It is also called the heat of the reaction because it tells you how much heat or KE was produced or consumed by the reaction.
Bond Energy (kJ)

7. PE + KE = Total Energy is constant
Conservation of Energy
PE KE ΔH Reaction Type
Decreases Increases -ve exothermic
Increases Decreases +ve endothermic
When PE (bond energy) decreases it is converted into KE which increases.
Remember that KE is heat energy, so it gets hotter and it is exothermic.

8. Ea (energy of activation)
Always +ve, given from outside

9. Required for forward reaction
Ea (Forward)
Required for forward reaction

10. Required for reverse reaction
Ea (Reverse)
Required for reverse reaction

11. Which reaction is fast? Forward or reverse?

12. Lets Explore the Potential Energy Changes during a Single Collision
H2 + I2 → 2HI KJ
1. An H2 and I2 approach each other

13. Lets Explore the Potential Energy Changes during a Single Collision
H2 + I2 → 2HI kJ
1. Reactants H2 and I2 approach each other
Reactants PE
Reaction Path

14. Lets Explore the Potential Energy Changes during a Single Collision
H2 + I2 → 2HI kJ
2. They collide and become an Activated Complex PE
Reaction Path

15. Lets Explore the Potential Energy Changes during a Single Collision
H2 + I2 → 2HI kJ
2. They collide and become an Activated Complex
Unstable
Reaction Intermediate
High PE Low KE
Bonds Break & Form
Reactant bonds break
Activated complex bonds form PE
Reaction Path

16. Lets Explore the Potential Energy Changes during a Single Collision
H2 + I2 → 2HI kJ
3. New bonds form and products separate PE
Reaction Path

17. Lets Explore the Potential Energy Changes during a Single Collision
H2 + I2 → 2HI kJ
3. New bonds form and products separate
activated complex bonds break
product bonds form PE
Reaction Path

18. Lets Explore the Potential Energy Changes during a Single Collision
H2 + I2 → 2HI kJ
3. New bonds form and products separate
Activated Complex
Reactants
Products PE
Reaction Path

19. Lets Explore the Potential Energy Changes during a Single Collision
H2 + I2 → 2HI kJ
3. New bonds form and products separate PE
Reaction Path
Ea(for)
Ea(rev)

20. Lets Explore the Potential Energy Changes during a Single Collision
H2 + I2 → 2HI kJ
3. New bonds form and products separate PE
Reaction Path Ea
Ea(rev)
ΔH = -ve

21. Relationship ship between Ea(f), Ea(r) and ΔH

22. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJ
H2 + I2 → 2HI ΔH = kJ
  600
400
200
PE (KJ)
Reaction Path

23. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJ
H2 + I2 → 2HI ΔH = kJ
  600
  reactants
400
200
PE (KJ)
Reaction Path

24. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJ
H2 + I2 → 2HI ΔH = kJ
  600
  reactants Ea
400
200
PE (KJ)
Reaction Path

25. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJ
H2 + I2 → 2HI ΔH = kJ
  600
  reactants Ea
400 ΔH
200
PE (KJ)
Reaction Path

26. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the activation energy is 200 kJ.
H2 + I2 → 2HI ΔH = kJ  
  600
  reactants Ea
400 ΔH
200
PE (KJ)
Reaction Path

27. Workbook Page 25
Question 41-45

28. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.
  I2 + Cl KJ → 2ICl
 PE
400
200
Reaction Path

29. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.
  I2 + Cl KJ → 2ICl
 PE
400
200
Reaction Path

30. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.
  I2 + Cl KJ → 2ICl
 PE
400
200
Reaction Path

31. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.
  I2 + Cl KJ → 2ICl
 PE
400
200
Reaction Path

32. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.
  I2 + Cl KJ → 2ICl
 PE
400
200
Reaction Path
ΔH = KJ

33. Draw the PE diagram if the enthalpy of the reactants is 400 kJ and the energy of the activated complex is 600 kJ.
  I2 + Cl KJ → 2ICl
 PE
400
200
Reaction Path
ΔH = KJ

34. Draw the PE diagram if the enthalpy of the reactants is 400 KJ and the energy of the activated complex is 600 KJ.
  I2 + Cl KJ → 2ICl
 PE
400
200
Reaction Path Ea
ΔH = KJ

35. Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ
  600
  400
  200
PE (KJ)
Reaction Path

36. Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ
  600
  400
  200
PE (KJ)
Reaction Path

37. Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ
  600
  400
  200
PE (KJ)
Reaction Path
Ea (rev) = 400 kJ

38. Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ
  600
  400
  200
PE (KJ)
Reaction Path
Ea (rev) = 400 kJ

39. Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ
  600
  Ea (for) = 200 kJ
  400
  200
PE (KJ)
Reaction Path
Ea (rev) = 400 kJ

40. Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ
  600
  Ea (for) = 200 kJ
  400
  200
PE (KJ)
Reaction Path
Ea (rev) = 400 kJ

41. Draw the PE diagram if the enthalpy of the products is 200 kJ, the Ea (for) = 200 kJ, and Ea (rev) = 400 kJ
  600
  Ea (for) = 200 kJ
  400
  200
PE (KJ)
Reaction Path
Ea (rev) = 400 kJ
ΔH = -200 kJ

42. Exothermic or Endothermic?
Exercise
Exothermic or Endothermic?

43. Exothermic or Endothermic?
Exercise
Forward reaction is
Exothermic or Endothermic?

44. Exothermic or Endothermic?
Exercise
Reverse reaction is
Exothermic or Endothermic?

45. What is Ea for forward reaction?
Exercise
What is Ea for forward reaction?

46. What is Ea for reverse reaction?
Exercise
What is Ea for reverse reaction?

47. Exercise Which species has strongest bond?
Clue: stronger the bond, higher the energy need to break the bond.

48. Exercise Which species has weakest bond?
Clue: stronger the bond, higher the energy need to break the bond.

49. What is ΔH for reverse reaction?
Exercise
What is ΔH for reverse reaction?

50. What is ΔH for forward reaction?
Exercise
What is ΔH for forward reaction?

51. What is activated complex?
Exercise
What is activated complex?

52. Which set of species has highest PE?
Exercise
Which set of species has highest PE?

53. Which set of species has highest KE?
Exercise
Which set of species has highest KE?

54. Which set of species has lowest KE?
Exercise
Which set of species has lowest KE?

55. Which set of species is fastest moving particles?
Exercise
Which set of species is fastest moving particles?

56. Which set of species is slowest moving particles?
Exercise
Which set of species is slowest moving particles?

57. Which reaction should be faster?
Exercise
Which reaction should be faster?
Forward or Reverse

58. Summary Activated complex
Breaking bond require energy and making bond give off energy
KE and PE conversion at collision
Speed of molecules based on KE
Stability of species based on PE
ΔH Forward/Enthalpy change
Ea (energy of activation) forward and reverse
Slow and fast reaction based on Ea
Strength of Bond based on Ea of reaction
Ea(f) Ea® ΔH relationship and calculation

59. Worksheet 1.2

60. KE Distribution Curve

61. Write two facts about this graph?
Distribution Curve
Write two facts about this graph?

62. Distribution Curve

63. Draw a Distribution Curve for student marks47 8 74 15 49 41 51 52 62 22 59 28 55 73 84 1 31 38 87 16 63 11 56 25 57 32 60 36 42
Write two facts about the distribution of marks

64. Draw a Distribution Curve for student marks
Write two facts about the distribution of marks
Is it a group of strong student or weak?
How will graph be different if it is not a group of strong students?

65. Kinetic Energy Distribution Curve

66. Kinetic Energy Distribution Curve
Are all molecules in this room moving?
Do they have KE?
Do all molecules have same amount o f KE?
Predict a distribution curve of KE of molecules?
How will KE distribution curve of a warm water flask
be different from an ice cube?

67. Kinetic Energy Distribution Curve

68. PE(kJ)
reaction path
Slow rate due to high Ea

69. PE(kJ)
500
400
300
200
100
reaction path
Increasing the temperature does not change the diagram. It gives more collisions the required Ea and more are successful.
Increasing the concentration, pressure, and surface area does not change the diagram.

70. Page 19 Question 29-30

71. Summary Activated complex
Breaking bond require energy and making bond give off energy
KE and PE conversion at collision
Speed of molecules based on KE
Stability of species based on PE
ΔH Forward/Enthalpy change
Ea (energy of activation) forward and reverse
Slow and fast reaction based on Ea
Strength of Bond based on Ea of reaction
Ea(f) Ea® ΔH relationship and calculation
KE distribution curve