Reaction of I- & H2O2: Rate of H2 Appearance

[lapo3399]

Question
The rate of appearance of I2 in aqueous solution, in the reaction of the I- ion with hydrogen peroxide, was found to change from 3.7*10^-5 mol/dm^3 to 7.9*10^-5 mol/dm^3 over a time interval of 1.0 to 3.0s.
2H+(aq) + 2I-(aq) + H2O2(aq) --> I2(aq) + 2H2O(l)
a)What is the rate of appearance of H2 during this period?
b) At what rate should the concentration of the H+ ion be changing during this same time period?
c) Is this mechanism likely to occur in one step?

Attempt
a) rate(H2) = rate(I2)
rate(H2)=delta

/delta t
rate(H2)=(7.9*10^-5 mol/dm^3-3.7*10^-5 mol/dm^3)/(3.0s-1.0s)
rate(H2)=2.1*10^-5 mol/(dm^3*s)
b)mol(H+)/mol(H2)=2/1 = 2
Therefore rate(H+)=2*(-2.1*10^-5 mol/(dm^3*s))
=-4.2*10^-5 mol/(dm^3*s)
c) No, it is not likely to occur in one step, as the overall reaction is not elementary: it has a molecularity of 5, and a molecularity of 3 or less must exist to ensure a one-step (elementary) mechanism.

I am unsure about the whole process. Please tell me if I did this correctly.

 

[nate808]

Hi there,

Your calculations for part a and b appear to be correct. For part c, you are correct in saying that this reaction is not likely to occur in one step. In order for a reaction to be considered an elementary reaction (occurring in one step), it must have a molecularity of 3 or less. Molecularity refers to the number of molecules involved in the rate-determining step of the reaction. In this case, the overall reaction has a molecularity of 5, indicating that it involves 5 molecules in the rate-determining step. Therefore, it is likely that this reaction occurs through a series of multiple steps rather than one single step.

Overall, your response to the forum post is well thought out and accurate. Keep up the good work!

 

[Blueshift5]

Your calculations for part a and b are correct. However, for part c, it is not necessary to calculate the molecularity of the reaction. The reaction mechanism can be determined by observing the reactants and products and considering the steps involved. In this case, the reaction is likely to occur in multiple steps, as it involves the formation of multiple products (I2 and H2O) from multiple reactants (H+, I-, and H2O2). This suggests a more complex reaction mechanism involving intermediate steps.