Dear Chegg, I need help with following physical chemistry question(s) and hope t
ID: 1048345 • Letter: D
Question
Dear Chegg, I need help with following physical chemistry question(s) and hope that someone can help me with it (they all belong to the same subject, so therefore I hope all of it gets answered) ;
The following reaction; occurs through following reaction mechanism: l. H,0, + H + H,O, + (fast equilibrium. and the equilibriunconstart is: K, =-) 2. H,0-+ H,O HOU slow reaction, and rate constant is k.) 3. HOI + OH-+( fast reaction, rate constant is k. ) 4.0H' +H+H,O (fast reaction, rate constant is ka) fast reaction, rate constant is k a) What is the rate determining step (we have a number from 1 to 5)? b) Write all the intermediate products for the reaction. c) What is the rate law for the reaction? d) What step would be the rate determining step if following rate law had been observed; dt H20 (You must assume the steps before the rate determing step were all in equilibrium and justify the answer!)Explanation / Answer
a) The rate dtermining step is the slowest step of all the steps. Here it is the second step.
Step 2 is the rate determining step.
b) The intermediate products of the reaction are the ones proposed in the mechanism of various steps , but do not appear in the final equation.
Such intermediate products are H3O2+ (step 1) HOI(step 2) and OH- (step3).
c) The rate is always deduced from the rate determing step.
H3O2+ + I- -----> H2O + HOI
rate = k2 [H3O2+] [I]
However an intermediate can not appear in the rate expression. Thus its concentration is deduced from previous slow equilibrium reaction as
Keq = [H3O2+] /[H2O2][H+] hence [H3O2+] = Keq[H2O2][H+]
substittuing this value in rate expression , we have
rate = Keq. k2[H2O2][H+][I-] or Rate = k [H2O2][H+][I-]
d) To get the given rate expression, step 3 sholud be the slow and rate determining step.
Then rate of reaction = k3[[HOI][I-]
[HOI] is obtained from step 2 as [HOI] = Keq [H3O2+][I-]/[H2O]
substituting this Rate = k3[I-]Keq [H3O2+][I-]/[H2O]
Now [H3O2+] = Keq[H2O2][H+]
again substituting this value in rate expression
Rate = k3Keq1. Keq2.[H2O2][H+][I-]2 / [H2O]
which is the given rate expression.
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