Mechanism Rate Law

Mechanism Rate Law - Rate Laws From Mechanisms Consider the...

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1 Chemical Kinetics Rate Laws From Mechanisms Consider the following reaction and its experimental rate law: and three possible mechanisms: 22 2 2NO ( ) F ( ) 2NO F( ) rate law [NO ][F ] obs gg g k + = Z ZX YZZ 1 –1 1 –1 2 –2 1 –1 2 –2 2 2 2 1: 2NO F 2NO F 2 : NO F NO F + F ( ) NO F NO F ( ) 3: NO F NO F + F ( ) NO F NO F ( ) k k k k k k k k k k Mechanism Mechanism slow fast Mechanism fast slow ⎯⎯→ + ←⎯⎯ + + + + Which mechanism(s) are possible? Chemical Kinetics Rate Laws From Mechanisms 2 • Rate laws are a reflection of the slow step in a reaction; one can use the elementary reactions shown in a mechanism to arrive at a rate law for it. For Mechanism 1, since there is ONLY one step: This does NOT match the experimental rate law so this mechanism must NOT be operative! 1 –1 2 2 12 2 2NO F [NO ] [F ] k k rate law k + =
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2 Chemical Kinetics Rate Laws From Mechanisms 3 For Mechanism 2, based on the slow step in the mechamism: This DOES match the experimental rate law so this mechanism is a possibility! BUT: what if Mechanism 3 were operative? 1 –1 2 –2 22 2 12 2 NO F NO F + F ( ) NO F NO F ( ) [NO ][F ] k k k k slow fast rate law k ⎯⎯→ + ←⎯⎯ + = Chemical Kinetics Rate Laws From Mechanisms-4
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This note was uploaded on 06/01/2009 for the course CHEM chem6ch taught by Professor Hoeger during the Spring '09 term at UCSD.

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Mechanism Rate Law - Rate Laws From Mechanisms Consider the...

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