rate law question

[theonlytycrane]

The given answer is (B) which refers to reaction 2 and not the mechanism. I was focusing on the slow step of the mechanism and wasn't sure if the rate law could be stated just based on reaction 2?

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[wizzed101]

S2O7 is both an intermediate and cannot appear in the rate law
in the fast step, at equilibrium: [S2O7] = k1*[O2] * [HSO3-]^2

The rate law per the slow step: rate = k2 * [S2O7] = k2 * k1 *[O2]*[HSO3-]^2

Substitute k1*k2 =k and you'll have the answer.

 

[aldol16]

The given answer is (B) which refers to reaction 2 and not the mechanism. I was focusing on the slow step of the mechanism and wasn't sure if the rate law could be stated just based on reaction 2?

It's asking for the rate law for the fast step only, which you can express as either appearance of S2O7 or H20 or disappearance of HSo3 or O2.

 

[theonlytycrane]

can't believe I missed that. thanks!

 

[poochimaster]

Wow! What a trick!! I also immediately assumed the question was asking you to define the rate law for the slow step instead of the fast step; great example of how important it is to slow down and read all of the words in the question stem.