Steady State Approximation

Steady State Approximation - Steady State Approximation...

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1 Steady State Approximation Steady-State Approximation Consider N 2 O 5 ( g ) 2 NO 2 ( g ) + 1/2 O 2 ( g ) Possible Mechanism: N 2 O 5 + M N 2 O 5 * + M (slow) k 1 k -1 N 2 O 5 * NO 3 + NO 2 (slow) NO 3 + NO 2 NO + NO 2 + O 2 (fast) NO 3 + NO 2 NO 2 (fast) k 2 k 3 k 4 “M” can be any molecule in the reaction
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2 Steady-State Approximation As N 2 O 5 * is a reactive intermediate, we can say the following regarding its formation and loss: Rate N 2 O 5 * formation = k 1 [N 2 O 5 ][M]; while Rate N 2 O 5 * loss = k -1 [N 2 O 5 * ][M] and Rate N 2 O 5 * loss = k 2 [N 2 O 5 * ] Therefore, the rate of change of [N 2 O 5 * ] (rate it is formed at - rate it is lost at) is: * ** 25 12 5 5 22 5 [] = [N O ][M] – [N O ][M] – [N O ] dNO kk k dt Steady-State Approximation The Steady-State approximation assumes that after a very short time the rate of intermediate production and loss are approximately equal, so: d [ N 2 O 5 * ] dt = 0 and: 5 5 5 [N O ][M] –
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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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Steady State Approximation - Steady State Approximation...

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