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Topic: law of mass action  (Read 6154 times)

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Demotivator

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law of mass action
« on: August 09, 2004, 03:45:10 PM »
aA + bB <> cC + dD
Keg = kf/kr= [C]c[D]d/[A]ab
Is the law of mass action rigorously true for equilibria problems or is it a magic show?
It makes the assumption that the rate of a reaction in a given direction is governed by a one step process.
This does not square with what I understand, that the rate is governed by the slowest step in a reaction
mechanism.
My question is, for problems involving equilibria in the real world is the law of mass action used as is, or is a modified version with experimentally determined coefficients used? If used as is, what is the justification?

Offline Mitch

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Re:law of mass action
« Reply #1 on: August 10, 2004, 09:01:34 PM »
It of course depends on the mechanism, in particular the slowest step.
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Offline Donaldson Tan

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Re:law of mass action
« Reply #2 on: August 12, 2004, 02:21:06 AM »
Mitch: Are u suggesting that the forward and backward equations in a chemical equilibrium are not the rate determining step?
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Re:law of mass action
« Reply #3 on: August 12, 2004, 09:56:28 PM »
From what I understood of the question, the particular equation above holds true. In the real world you don't have equilibrium like that, when you go from starting material to product there are intermediates, those intermediates also have to be incorporated into the rate equation. Since the question asked how it was done in the real world, I answered it accordingly.
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