1. Rates of Chemical Reactions
Chapter 6

3. Things that Affect Rate
Temperature
Higher temperature faster particles.
More and harder collisions.
Faster Reactions.
Concentration
More concentrated closer together the molecules.
Collide more often.
Faster reaction.

4. Things that Affect Rate
Particle size
Molecules can only collide at the surface.
Smaller particles bigger surface area.
Smaller particles faster reaction.
Smallest possible is molecules or ions.
Dissolving speeds up reactions.
Getting two solids to react with each other is slow.

5. Things that Affect Rate
Catalysts- substances that speed up a reaction without being used up.(enzyme).
Speeds up reaction by giving the reaction a new path.
The new path has a lower activation energy.
More molecules have this energy.
The reaction goes faster.
Inhibitor- a substance that blocks a catalyst.

23. AP enrichment

27. AP enrichment

28. AP enrichment

35. H O H2O
Energy
Reactants
Products
Reaction coordinate

36. Activation Energy - Minimum energy to make the reaction happen
Reactants
Products
Reaction coordinate

37. Activated Complex or Transition State
Energy
Reactants
Products
Reaction coordinate

38. Energy
Reactants
Overall energy change- ∆H
Products
Reaction coordinate

47. Catalysts- heterogeneous gas and solid
Hydrogen bonds to surface of metal.
Break H-H bonds H H H H
Pt surface

48. Catalysts H H C C H H H H H H
Pt surface

49. C C Catalysts Pt surface
The double bond breaks and bonds to the catalyst. H H H C C H H H H H
Pt surface

50. C C Catalysts Pt surface The hydrogen atoms bond with the carbon H H H

51. Catalysts H H C C H H H H H H
Pt surface

52. Reaction Mechanism
Elementary reaction- a reaction that happens in a single step.
Reaction mechanism is a description of how the reaction really happens.
It is a series of elementary reactions.
The product of an elementary reaction is an intermediate.
An intermediate is a product that immediately gets used in the next reaction.

53. This reaction takes place in three steps

54. Ea
First step is fast
Low activation energy

55. High activation energyEa
Second step is slow
High activation energy

56. Ea
Third step is fast
Low activation energy

57. Second step is rate determining

58. Intermediates are present

59. Activated Complexes or Transition States

60. Mechanisms and rates
There is an activation energy for each elementary step.
Slowest step (rate determining) must have the highest activation energy.

61. Slow Step and Reaction Order
Given a proposed reaction mechanism,
The sum of all the elementary steps should add up to the overall reaction
The proposed reaction coefficients of the SLOW step should match the overall reaction rate order.
2 Proposals for the Destruction of Ozone:
Sum: Sum:
2O3(g) = 3O2(g) 2O3(g) = 3O2(g)
Evidence gathered experimentally shows that the destruction of ozone is a first order reaction
THUS the CORRECT REACTION MECHANISM IS THE ONE ON THE LEFT
O3(g) = O2(g) + O(g) SLOW O3(g) + O3(g) = O2(g) + O4(g) SLOW
O(g) + O3(g) = O2(g) + O2(g) FAST O4(g) = O2(g) + O2(g) FAST