Lec 08 Jan 21 Wed - 1.23 7. Catalysis: speeding up a...

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1.23 7. Catalysis: speeding up a reaction (Sect 14-11) Can increase the rate of a reaction by : - increasing temperature (which increases k ) - using a catalyst (when you can’t use a higher T ) Catalyst : a substance that increases the rate but is not consumed during the reaction. therefore you only need a little catalyst works by providing a different mechanism and a different transition state for the reaction. This new reaction pathway has a lower E a has no influence on Δ H (this depends only on initial and final states (independent of pathway) Biology: catalysts are enzymes Chemistry: catalysts are often transition metals A. Homogeneous Catalysis = catalyst is in the same phase as the reactants (usually both in solution) e.g. Decomposition of H 2 O 2 (aq) catalyzed by I - (say from KI(aq) ): 1. H 2 O 2 (aq) + I - (aq) OI - (aq) + H 2 O (l) Slow 2. H 2 O 2 (aq) + OI - (aq) H 2 O (l) + O 2 (g) + I - (aq) Fast Overall : 2 H 2 O 2 (aq) 2 H 2 O (l) + O 2 (g) k 1 k 2
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Lec 08 Jan 21 Wed - 1.23 7. Catalysis: speeding up a...

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