The Rate Law in Chemistry

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"The Rate Law" in Chemistry

Hey I've just been working on a chemistry lab lately in my chemistry course, and one of the problems on the lab write-up asks to:

Write the rate law for the following reaction, if it were to occur through a single-step mechanism.
2I^-(aq) + S2O8^2-(aq) -> 2SO4^2-(aq) + I2(aq)

Now since it is asking to write it as a single-step mechanism I would assume there is only one step needed.

Now in the lab it has given us this formula:

rate = -(delta[S2O8^-2])/(delta t) = -(1/2)(delta [I^-])/(delta t) = (1/2)(delta[SO4^2-])/(delta t) = (delta[I2])/(delta t)

So could you not just say the only step needed is:
-(delta[S2O8^-2])/(delta t) = (delta[I2])/(delta t)

Then for the second part to the question it asks "By examination of the experimentally determined rate law, explain whether this reaction does in fact proceed through a single-step mechanism. Explain."

Any help on this problem would be great, thanks.
 

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  • #2
GCT
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The rate law would be

rate=k(forward)[I-]^2[S2O8]

does your experimentally determined rate law concur with this expression?
 
  • #3
GCT
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The rate law would be

rate=k(forward)[I-]^2[S2O8]

does your experimentally determined rate law concur with this expression?
 
  • #4
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Ahh I see what you are saying, yeah it's just
rate=k[S2O8^2-][I^-]^2

And my rate law does not coincide with this, therefore it cannot be a single-step mechanism. Gotcha! Thanks.
 
Last edited:

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