1. Catalysts:
Speed up reaction rates by offering an alternate reaction pathway with a lower activation energy
How they work …
Remember “collision theory” from yesterday
1. The reacting molecules must collide with one another
2. The reacting molecules must collide w/ sufficient energy to initiate the breaking and forming bonds
3. The molecules must collide in an orientation that can lead to the proper rearrangement of products

2. Catalysts:
Types:
1. Surface catalysts – reacting particle attaches to catalytic surface, exposing the part of the molecule that is able to react
Examples – metals (Pt, Ni, etc)
3. The molecules must collide in an orientation that can lead to the proper rearrangement of products

3. Catalysts:
Types:
2. Enzyme catalysts– enzymes are large, biological molecules (proteins) with very specific and complex shapes
3. The molecules must collide in an orientation that can lead to the proper rearrangement of products

4. Catalysts:
Types:
2. Enzyme catalysts– enzymes are large, biological molecules with very specific and complex shapes
3. The molecules must collide in an orientation that can lead to the proper rearrangement of products

5. Catalysts:
Types:
3. Acid-base catalysts– look for common acids and bases (HCl, H2SO4, NaOH, NH3)
3. The molecules must collide in an orientation that can lead to the proper rearrangement of products

6. Reaction Mechanisms:
The sequence of bond-making and bond-breaking steps of a reaction
These steps are often called elementary steps
A proposed mechanism is always theoretical, can not be proven

7. Reaction Mechanisms: Example: Br2 + 2 NO  2 BrNO
Is this rxn likely to happen in 1 step?
NO!!! NO
3 particles would have to collide simultaneously, in exactly the right orientation, which is very unlikely …
Br2 NO

8. Reaction Mechanisms: Example: Br2 + 2 NO  2 BrNO Elementary Steps

9. Reaction Mechanisms: Example: Br2 + 2 NO  2 BrNO Elementary Steps

10. Reaction Mechanisms: Example: Br2 + 2 NO  2 BrNO Elementary Steps
2. Br2NO + NO  BrNO + BrNO

11. Reaction Mechanisms: Example: Br2 + 2 NO  2 BrNO Elementary Steps
2. Br2NO + NO  BrNO + BrNO
Show that these mechanism steps give the correct net reaction.

12. Reaction Mechanisms: Br2 + 2 NO  2 BrNO Elementary Steps
2. Br2NO + NO  BrNO + BrNO
What would the reaction coordinate diagram look like if the activation energy for the net reaction is 100 kJ and it is known to be exothermic?

13. Reaction Mechanisms: The decomposition of ozone … Elementary Steps
1. Cl + O3  O2 + ClO
2. ClO + O3  Cl + 2O2
What is the net reaction?
ID any intermediates, catalysts, reactants and products.

14. Reaction Mechanisms: The decomposition of ozone … Elementary Steps
1. Cl + O3  O2 + ClO
2. ClO + O3  Cl + 2O2
A different catalyst is introduced that adds 2 steps to the proposed mechanism as represented above. Which step is the slowest?

15. Reaction Mechanisms: H+ + I- + H2O2  H2O + HOI Elementary Steps
1. H+ + H H2O2  H4O2+2
2. Propose a second step in the mechanism

16. Reaction Mechanisms: H+ + I- + H2O2  H2O + HOI Elementary Steps
1. H+ + H H2O2  H4O2+2
2. H4O I-  H2O + HOI + H+
This reaction is known to be very fast. Do you agree with this proposed mechanism?

17. Practice On Your Own:

18. Practice On Your Own: