Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Kuahji on March 01, 2008, 08:07:44 PM
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Does anyone know where I can find a good guide to rate mechanisms? I'm having a lot of trouble trying to figure out if an elementary is slow or fast or how everything is related.
Here is an example question
When the concentration of A is doubled, the rate for the reaction: 2 A + B-> 2 C quadruples. When the concentration of B is doubled the rate remains the same. Which mechanism below is consistent with the experiment observations?
The answer is (it was multiple choice, but I'll just post the correct answer)
Step 1: 2A -> D (slow)
Step 2: B + D -> E (fast)
Step 3: E-> 2 C (fast)
So I just look at it & wonder how... I just don't get it.
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I think that statement, When the concentration of B is doubled the rate remains the same.", implies that B is not a reagent in the rate-determining step, which is the elementary step that has the slowest rate. And "When the concentration of A is doubled, the rate for the reaction: 2 A + B-> 2 C quadruples" implies that the stoichiometric coefficient of A is twice, according to the Rate Law.
So the rate law is probably like ... Rate = [A]2
Find out more about the topic: try http://en.wikipedia.org/wiki/Reaction_rate
P.S. I don't speak English so my skills are poor. Hope you understand me.