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Chemistry 1011 Slot 51 Chemistry 1011 TOPIC Rate of Reaction TEXT REFERENCE Masterton and Hurley Chapter 11
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Chemistry 1011 Slot 52 11.5 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.
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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
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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
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Chemistry 1011 Slot 55 Effect of a Catalyst on the Activation Energy
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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
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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
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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
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