Chemistry 1011 Slot 51 Chemistry 1011 TOPIC Rate of Reaction TEXT REFERENCE Masterton and Hurley Chapter 11

Chemistry 1011 Slot Catalysis YOU ARE EXPECTED TO BE ABLE TO: Identify heterogeneous and homogeneous catalysts in chemical and biological systems. Describe heterogeneous and homogeneous catalytic processes. Interpret catalysis in terms of the effect on activation energy.

Chemistry 1011 Slot 53 What is a Catalyst? A catalyst is a substance that increases the rate of a reaction without being consumed A heterogeneous catalyst is in a different phase from the reaction mixture A homogeneous catalyst is in the same phase as the reaction mixture

Chemistry 1011 Slot 54 Heterogeneous Catalysts Many transition metals can adsorb gas molecules onto their surface This involves the formation of a weak “bond” using metal d electrons The molecules can then react and the products desorb The metal provides an alternative path, with a lower activation energy Example: catalytic converters

Chemistry 1011 Slot 55 Effect of a Catalyst on the Activation Energy

Chemistry 1011 Slot 56 Homogeneous catalysts Most homogeneous catalysts join in the reaction A reaction intermediate is formed The reaction intermediate decomposes to give reaction products and regenerating the catalyst

Chemistry 1011 Slot 57 Example of Homogeneous Catalysis 2H 2 O 2(aq)  2H 2 O (l) + O 2(g) This reaction proceeds slowly, but can be catalyzed by I  ions H 2 O 2(aq) + I  (aq)  H 2 O (l) + IO  (aq) H 2 O 2(aq) + IO  (aq)  H 2 O (l) + O 2(g) + I  (aq) I  (aq) ions are regenerated – not used up

Chemistry 1011 Slot 58 Enzymes Catalysts in living organisms are called enzymes Many are proteins with high molar masses Many enzymes are very specific –Eg: maltase will catalyze the hydrolysis of maltose to glucose Most enzymes operate only over a very narrow temperature range