Lec-07-Chap13omplete

Lec-07-Chap13omplete - Lec-07: Reaction Mechanisms;...

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Unformatted text preview: Lec-07: Reaction Mechanisms; Catalysis Chapter 13 11 CHE 132 First Midterm - Review Session: Sunday September 20, 3:00 - 6:00 PM Old Chemistry Building, Room 116 Reaction Mechanisms and Rate Laws Most chemical reactions do not occur in a single step; instead they involve a sequence of unimolecular or bimolecular elementary reaction steps . As an illustration consider the reaction ( 29 ( 29 ( 29 2 2 2 2 NO g F g 2 NO F g + → Experimentally it is found that the rate law is [ ] [ ][ ] 2 exp 2 2 NO 1 rate NO F 2 d k dt = - = That the rate law is of first order with respect to NO2 (instead of 2) shows that the reaction involves more than one step . 22 Reaction Mechanisms and Rate Laws ( 29 ( 29 1 2 2 2 2 2 2 slo NO F N NO w fa F F F NO + t O + s F k k + → → The accepted mechanism for the reaction is We see that the mechanism is consistent with the overall stoichiometry. We now analyze the mechanism to verify that it is consistent with rate law. To do so we recognize that the products cannot be formed faster than the rate of the slowest step in the mechanism sequence . ( 29 ( 29 ( 29 2 2 2 2 NO g F g 2 NO F g + → 33 Reaction Mechanisms and Rate Laws ( 29 ( 29 1 2 2 2 2 2 2 slo NO F N NO w fa F F F NO + t O + s F k k + → → The slowest elementary process in a sequence is called the rate determining step . [ ] [ ][ ] 2 1 2 2 NO 1 r N at 2 F e O k d dt = - = This is an example of a mechanism with a slow initial step . Then it is straightforward to recover the rate law . In this mechanism F is referred to as a reaction intermediate ....
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This note was uploaded on 01/02/2010 for the course CHE 132 taught by Professor Hanson during the Fall '08 term at SUNY Stony Brook.

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Lec-07-Chap13omplete - Lec-07: Reaction Mechanisms;...

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