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Topic: Rate law and mechanism  (Read 3275 times)

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Offline LHM

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Rate law and mechanism
« on: January 15, 2011, 05:48:18 PM »
For the reaction:
2 H2(g) + 2 NO(g) :rarrow: N2(g) + 2 H2O(g)
This mechanism is proposed:
step 1: H2 + NO :rarrow: H2O + N
step 2: N + NO :rarrow: N2 + O
step 3: O + H2 :rarrow: H2O

If we're given that the 2nd step is the rate law, then how come rate=k[H2][NO]2, instead of rate=k[H2][NO]2/[H2O]? Like why can just disregard the [H2O], since it's a gas in the overall equation?

Offline samiam

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Re: Rate law and mechanism
« Reply #1 on: January 15, 2011, 05:59:10 PM »
what?
You are saying step 2 is the rate law? so the rate determining step i.e. the elementary step that limits the overall rate of reactions.

than the rate law would be r=k[N][NO] it does not depend on the products.

Offline LHM

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Re: Rate law and mechanism
« Reply #2 on: January 15, 2011, 06:03:29 PM »
what?
You are saying step 2 is the rate law? so the rate determining step i.e. the elementary step that limits the overall rate of reactions.

than the rate law would be r=k[N][NO] it does not depend on the products.


Oh oops, I'm sorry! I meant that step 2 is the rate determining step.

Offline LHM

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Re: Rate law and mechanism
« Reply #3 on: January 17, 2011, 12:22:07 PM »
But it's highly unlikely that the answer key's wrong, which means that the rate law is rate=k[H2][NO]2, so do you or anyone else know why it's this?

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