Lecture 10 - 1/27/10 e.g. The hydrogenation of ethylene to...

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1/27/10 1 e.g. The hydrogenation of ethylene to make ethane is : Overall : H 2 (g) + C 2 H 4 (g) ! C 2 H 6 (g) Metal catalyst (usually Ni, Pt or Pd) splits H-H bond in H 2 (g) 2. 2 Metal (s) + H 2 (g) ! 2 Metal-H (s) (Slow) 3. 2 Metal-H (s) + C 2 H 4 (g) ! C 2 H 6 (g) + 2 Metal (s) 4. Escape, or desorption, of products k 1 k 2 1. Reactants adsorb onto the surface (active sites) 105 Rate = k 1 [H 2 ] Solids do not have a concentration metal Rate of slowest step (RDS) Overall rate = - do not appear in rate law In cars, catalytic converters (platinum, rhodium), help split the bonds in CO (g) and NO (g). There is a reduction catalyst, to reduce NO (g) to N 2 (g), and an oxidation catalyst to oxidize CO (g) to CO 2 (g). So what could cause the catalyst to stop working? 106 Other substances bind to surface and won’t come off “Poison” the catalyst Think of the heterogeneous reaction mechanism - Reactants bind to the metal - No binding = no catalytic activity Jimmy is trying to compare two different reactions. For reaction (1), 2N 2 O 5 ! 2N 2 O 4 + O 2 He measures t 1/2 = 1116 s for [N 2 O 5 ] 0 = 0.0100 M ! [N 2 O 5 ] t = 0.0050 M For reaction (2), 2 C 4 H 6 ! C 8 H 12 He measures t 1/2 = 1630 s for [C 4 H 6 ] 0 = 0.0100 M ! [C 4 H 6 ] t = 0.0050 M Which of the following is true regarding the rate constants?
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This note was uploaded on 04/22/2010 for the course CHEM 102 taught by Professor Brown during the Winter '10 term at University of Alabama at Birmingham.

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Lecture 10 - 1/27/10 e.g. The hydrogenation of ethylene to...

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