Which mechanism and which step would best fit the data?

AI Thread Summary
Two proposed mechanisms are being evaluated to determine which best fits the experimental data and identifies the rate-determining step. The discussion highlights the need to analyze the effects of varying concentrations of reactants, specifically [I-], [H2O2], and [H+], on the reaction rate. It is suggested that the rate law can be derived from this analysis, indicating that [H+] may be an intermediate since it does not appear in the final rate law. Participants are encouraged to calculate the rate laws for different cases to clarify the relationship between reactant concentrations and the rate-determining step. Understanding these relationships is crucial for accurately identifying the mechanism that aligns with the observed data.
JessicaHelena
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Homework Statement


Two mechanisms are proposed (as seen in the screenshot). Which mechanism and which step as the rate determining step would best fit the data?

Homework Equations


I think this is more of a conceptual problem ...

The Attempt at a Solution


I apologise for not strictly following this format, but I am really lost, because the teacher didn't really teach us much about comparing the best-fit mechanisms and steps. How do I compare between the two? Both look equally good to me.
 

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Wasn't there any data given? Perhaps in earlier questions?
 
Oh, I believe it might be this data that they're referring to...
 

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Could anyone help me with this? I do have a test on this tomorrow, and I'd really like some help...
 
Compare I and II. What is the effect on the rate of doubling [I-] while keeping everything else constant? So how does the rate depend on [I-]?
Compare II and III. What is the effect of doubling [H2O2]?
Compare III and IV. Here you double both [H2O2] and [H+]. But you have already determined the effect of doubling [H2O2]. So what is the effect of doubling [H+]?
Now you know the dependence of the rate on the 3 concentrations, what does that tell you about the rate-determining step?
 
@mjc123
So from your questions, I can get the rate law, which would be something like
Rate = k*[H_2O_2]*[I^-], and we can plug in any row's data to find k.

However, I'm not sure what this tells me about the rate-determining step...
 
So if the rate law doesn't involve [H+], does that tell you anything?
 
@mjc123 So [H^+] would be the intermediate? (Since intermediates are canceled between the steps)
 
Try working out what the rate law would be in cases A-D.
 

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