bioex_lect33

bioex_lect33 - 2 is equal to 2 times the rate of the slow...

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MIT OpenCourseWare http://ocw.mit.edu 5.111 Principles of Chemical Science Fall 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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Reaction Mechanism See lectures 32 and 33 for determining reaction mechanisms. Example from pg. 4 of Lecture 33 notes: The reaction mechanism of natural ozone depletion: Through a variety of catalytic cycles, Cl and Br ions catalyze the destruction of ozone in the stratosphere. However, at high concentrations, ozone decays into oxygen without metal catalysts required: 2O 3 3O 2 proposed mechanism: k 1 Step 1 O 3 O 2 + O rate f = k 1 [O 3 ] (fast k -1 reversible) rate r = k -1 [O 2 ][O] k 2 Step 2 O + O 3 O 2 + O 2 rate= k 2 [O][O 3 ] (slow) The rate is determined by the slowest step The rate of formation of O
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Unformatted text preview: 2 is equal to 2 times the rate of the slow step (k 2 [O][O 3 ]), since two molecules of O 2 are formed. Thus, rate of formation of O 2 = 2k 2 [O][O 3 ], but O is an intermediate, solve for O in terms of products and reactants and rate constants. Since the first step is fast and reversible and the second step is slow, the first step is in equilibrium and we can write [O 2 ][O] = k 1 = K 1 or [O] = k 1 [O 3 ] [O 3 ] k-1 k-1 [O 2 ] substituting: rate = 2k 2 k 1 [O 3 ] 2 k-1 [O 2 ] rate = k obs [O 3 ] 2 [O 2 ] What is the order in O 3 ? 2 double O 3 /rate will? multiply by 4 What is the order in O 2 ? -1 double O 2 / multiply by What is the overall order? 1 double both O 3 and O 2 / double...
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This note was uploaded on 03/02/2012 for the course CHEM 5111 taught by Professor Vogel during the Fall '08 term at MIT.

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bioex_lect33 - 2 is equal to 2 times the rate of the slow...

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