1. Catalysts Mak-3-ram Kamale-2-dine

2. Catalyst review A catalyst provides an alternative reaction pathway that requires less activation energy (topic 5: enthalpy/topic 6: kinetics) Types: – Homogeneous Same phase as reactants – Heterogeneous Different phase than reactants

3. C.4.1 Compare the modes of action of homogeneous and heterogenous catalysts Homogeneous catalysts can produce intermediate compounds in a reaction during the reaction process. However they are regenerated and will eventually return to the original state. Transition metal ions make great catalysts because they occupy more than one oxidation state. Example : Fe 2+ oxidizes to Fe 3+ and then back to Fe 2+ in the reaction between S 2 O 8 2- and an I - ion.

4. C.4.1 Compare the modes of action of homogeneous and heterogenous catalysts Heterogenous catalysts function by adsorption. Adsorption is when molecules of the reactant are adsorbed onto the surface of the catalyst and they are orientated correctly to react with the other reactant molecules. Transition metals (group 3) are frequently used adsorbents in industrial processes.

5. C.4.1 Compare the modes of action of homogeneous and heterogenous catalysts An active site is the region of the catalyst which binds to the reactant. A good catalyst will allow a reactant to adsorb to the surface at the active site, but release it once the product is formed. Catalysts such as tungsten can adsorb too strongly and not release the reactant molecules, making it non-effective as a catalyst.

6. C.4.1 Compare the modes of action of homogeneous and heterogenous catalysts The shape of the catalyst can be important in their effectiveness. Enzymes are common biological catalysts. Often heat or changes in pH will denature the enzyme, changing the shape and making the active site no longer available. Any time the shape changes which blocks the active site, the catalyst is no longer effective.

7. C.4.2 Outline the advantages and disadvantages of homogenous and heterogenous catalysts. Homogenous Catalysts Advantages: – All the catalyst is exposed to the reaction (more active site volume) – Can be used more easily to make one single product using a catalyst which has unique active sites. Disadvantages: – Can be difficult to remove from the reaction mixture.

8. C.4.2 Outline the advantages and disadvantages of homogenous and heterogenous catalysts. Heterogenous Catalysts Advantages: – Easily removed by filtration – Long life, and are less specific so they can be used for other reactions. Disadvantages – Only effective on the surface used for adsorption. – Surface might not become usable after thorough usage. (Coating on surface reduces activity)

9. C.4.3 Discuss the factors in choosing a catalyst for a process. Selectivity: will the catalyst produce only the desired product? Efficiency: will the catalyst effectively lower the E a of the reaction? Will it work well in extreme conditions (high pressure/temperature)? Environmental impact: will the catalyst produce intermediate compounds that are harmful to the environment?

10. C.4.2 Outline the advantages and disadvantages of homogenous and heterogenous catalysts. Poison Potential: a poison can block the active site of a heterogeneous solid catalyst from the reactants. Cost: nickel is cheaper than palladium and platinum, but is it more effective as a catalyst?