: Rate of Reaction of Acetone with lodine: What does the rate law tell us abo th

Question

: Rate of Reaction of Acetone with lodine: What does the rate law tell us abo the steps by which the reaction may occur? H30++ H20 (R1) acid catalyzed fast keto intermediate formation +H20 H30+ (R2) H3C CH3 keto enol rate-determining keto enol reaction I2 + H2O (R3) + +H30+ rapid halogenation of enol Equation (3) expresses the quickly obtained relationship where the forward reaction qual to the backward reaction r, for reaction (R1). Because these are elementary single collision steps, we can express the rate for each step from the chemical equation. k, [acetonel [H,01 k,[keto] Because the intermediate keto form cannot appear in the final rate law we need to express it in terms of the reactants. Rearranging to solve for the keto intermediate from Eq. stated in Eq. (4). (keto--[acetone] [H301 k.j From the mechanism we can see that r2 is the rate determining step, rate r, and is expressed in Eq. (5). Substituting [keto] from Eq. (4) we obtain Eq. (6). For completeness, it should be noted that we are making use of the assumption of negligible reverse reaction for (R2) as mentioned above. 2-k2[keto] kzk rate = r2 = [acetone] [H301 Combining the individual step k's into one overall k gives Eq. (7) rate = k [acetone] [H301 87

Explanation / Answer

1) Example from real life situation that fits the above mechanism:

To transfer liquid through a long neck narrow funnel:

1) You pour a liquid through a long neck funnel,the liquid accumulate at the (cup -shaped) mouth of the funnel (fast ,doesn't take time)

2) The rate of liquid flow depends on the radius of the cylindrical neck,for very small rate the process of liquid movement is greatly slowed down (slow,rate determining step)

3) The liquid after passing through the neck immediately fills the beaker placed at its exit end (fast process)

a)Rate determining step is the slowest of all the step involved in the reaction mechanism.This step ony is used to predict the actual rxn rate.In the example ,described above ,the liquid passes through the narrow neck slowly so this step is rate determining.

b)The rxn has three step mechanim:

2N2O5 --->4NO2 +O2

step 1) N2O5 <---Kf/Kr--->NO2+NO3(fast rxn) [Kf=forward rxn rate constant,Kr=reverse rxn rate constant]

step 2)NO3+NO2 (N2O5)--K1--->NO +NO2 +O2 ( k1=rxn rate contnt) [Rate determining step)

step3) NO3+NO ---K2--->2NO2 (fast rxn)

rate=k[N2O5]

c) fast forward process before RDS,N2O5 ---Kf--->NO2+NO3(fast rxn)

d)N2O5 <---Kr---NO2+NO3(fast rxn)

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