Multistep Reaction Kinetics

[homestar]

I saw a multistep reaction kinetics question in some test prep material. I can't remember the details of the question, but I thought that it was particularly difficult and I can't find info on it easily (I've looked reasonably diligently).

A multistep chemical reaction was presented as an example.

The question asked to determine an equation for the reaction rate. It provided a few options, and I believe they were:

"the reaction rate is the negative slope of the change in reactant concentration over time"

"the reaction rate is the negative slope of the logarithm of the change in reactant concentration over the change in time"

"the reaction rate is the negative slope of the logarithm of the change in INTERMEDIATE concentration over the change in time"

etc...

Any thoughts? I've just never encoutered differential equations involving logarithms modelling multistep reaction kinetics in my pre-med studies.

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[fizzgig]

i dunno if this is correct but they're not asking you to set up a diffeq or anything. if a single step elementary reaction is 1st 2nd 3rd order or whatever you have those graphs that show you how concentration changes over time (which involve logs or 1/[x] or whatever makes the relationship a straight line).

now if you have a multi step i would assume they just want you to 1)decide which is the rate determining step. if it's step 1, just use the step 1 reactants. if it's a later step then (assuming the other steps are very fast and plenty of intermediate is made) use that step's equation, so you're using intermediate concentrations.

2)they would have had to give you info to determine reaction order, and thats how you decide if it's [x], 1/[x], or the one involving log x that i cant' remember vs time on the graph...