1. Catalysts
Rates of Reactions

2. A Catalyst is…
A substance that alters (speeds up or slows down) the rate of a chemical reaction but is not consumed in the reaction

3. Positive & Negative Positive catalysts = speed up a reaction
Manganese dioxide, amylase
Negative catalysts (inhibitors) = slow down a reaction
Glycerine in H2O2, Calcium propionate to preserve bread

4. A. Properties of Catalysts
Chemically unchanged
Specific
Lipase = fats
Pepsin = protein
Amylase = starch
Sucrase = sucrose
Small amounts effective
Equilibrium reached more quickly
Can be poisoned

5. B. Types of Catalysis Homogeneous Catalysis Hetrogeneous Catalysis
Same Phase = no boundary between the reactants and catalyst
Eg. both liquids
Hetrogeneous Catalysis
Different phases = a boundary exists
Eg. A liquid and a solid
Autocatalysis
One of the products catalyses the reaction
Eg. Potassium permanganate & ammonium iron (II) sulfate (Mn2+)

6. C. Mechanisms 1. Intermediate Formation Theory
2. The Surface Adsorption Theory

7. C1. Intermediate Formation Theory
Reactant 1 + Catalyst → Intermediate compound
Intermediate compound + Reactant 2 → Product + Catalyst

8. Particles must collide with each other
Collision Theory
Particles must collide with each other
A certain minimum energy needs to be reached before products are formed

9. Activation Energy
Is the minimum amount of energy needed by colliding particles for a reaction to occur
Size of A.E. depends on the nature of reactants
A.E. determines the rate of reaction

10. Maxwell – Boltzmann Distrubution

11. Reaction Profile Diagram

12. A = Reactants, B = Products

13. Activation Energies & Rates
Low activation energy = fast rate of reaction
High activation energy = slow rate of reaction

14. Effect of Catalyst on Reaction
Catalyst = lowers the activation energy (provides an alternative reaction pathway)

15. Recap on Factors Affecting Rate of Reaction
Nature of Reactants : covalent = slow as bonds must be broken so have higher Activation Energy, ionic = fast
Particle Size : Smaller particle size = more surface area exposed = number of collisions increased = greater number of effective collisions = faster rate of reaction
Concentration : Higher concentration = number of collisions increased = greater number of effective collisions = faster rate of reaction
Temperature = number of high energy reactants increases = greater number of effective collisions = faster rate of reaction
Catalyst : Lowers Activation Energy by providing an alternative reaction pathway = faster rate of reaction