1. Kinetics
Lesson 4
PE Diagrams

2. Potential Energy Diagrams
Kinetic Energy (kJ)
Heat energy due to the motion of particles. Simulation
Potential Energy or Enthalpy (H).
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)

3. 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.

4. 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

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

6. 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

7. 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

8. 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

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

10. 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

11. 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

12. 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)

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. Potential Energy Diagrams Endothermic
Standard Notation:
I2 + Cl kJ → 2ICl
ΔH Notation:
I2 + Cl2 → 2ICl ΔH = kJ
Both notations indicate an endothermic reaction. The first indicates that 100 kJ of KE are consumed, while the second shows that the PE increases by 100 kJ.
on left
or positive

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. Exothermic Reaction

35. Exothermic Reaction
Uncatalyzed reaction

36. Exothermic Reaction
Uncatalyzed reaction
Catalyzed reaction

37. Exothermic Reaction
Reactants
Products

38. Exothermic Reaction
Reactants
Products
stronger bonds

39. Exothermic Reaction
Downhill in PE
KE is produced

40. Exothermic Reaction
Downhill in PE
KE is produced
Ea(for)(uncat)

41. Exothermic Reaction Downhill in PE KE is produced Ea(for)(uncat)
Ea(for)(cat)

42. Exothermic Reaction Downhill in PE KE is produced Ea(for)(uncat)
Ea(for)(cat) H

43. Exothermic Reaction Downhill in PE KE is produced Ea(for)(uncat)
Ea(for)(cat)
Ea(rev)(cat) H

44. Exothermic Reaction Downhill in PE KE is produced Ea(for)(uncat)
Ea(rev)(uncat)
Ea(for)(cat)
Ea(rev)(cat) H

45. PE(kJ)
500
400
300
200
100
reaction path
H forward =
H reverse =
Ea forward uncat =
Ea reverse uncat =
Ea forward cat =

46. PE(kJ)
500
400
300
200
100
reaction path
H forward = -300 kJ
H reverse =
Ea forward uncat =
Ea reverse uncat =
Ea forward catalyzed =

47. PE(kJ)
500
400
300
200
100
reaction path
H forward = -300 kJ
H reverse = +300 kJ
Ea forward uncat =
Ea reverse uncat =
Ea forward catalyzed =

48. PE(kJ)
500
400
300
200
100
reaction path
H forward = -300 kJ
H reverse = +300 kJ
Ea forward uncat = 100 kJ
Ea reverse uncat =
Ea forward catalyzed =

49. PE(kJ)
500
400
300
200
100
reaction path
H forward = -300 kJ
H reverse = +300 kJ
Ea forward uncat = 100 kJ
Ea reverse uncat = 400 kJ
Ea forward catalyzed =

50. PE(kJ)
500
400
300
200
100
reaction path
H forward = -300 kJ
H reverse = +300 kJ
Ea forward uncat = 100 kJ
Ea reverse uncat = 400 kJ
Ea forward catalyzed = 50 kJ

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

52. PE(kJ)
reaction path
The only way to change the PE diagram is to add a catalyst.

53. PE(kJ)
reaction path
The only way to change the PE diagram is to add a catalyst.
More low energy collisions are successful!

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

55. 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.