For a reaction 2H_2O_2 I^-/alkaline medium ->2H_2O+O_2 the proposed mechanism is as given below: (I) H_2O_2 + I^ – → H_2O + IO^ – (slow)

Question

For a reaction

2H₂O₂\(\frac{I^-}{\text{alkaline medium}}\to\)2H₂O+O₂

 the proposed mechanism is as given below: 

(I) H₂O₂ + I^– → H₂O + IO^–  (slow) 

(II) H₂O₂ + IO^– → H₂O + I^– + O₂  (fast) 

(a) Write rate law for the reaction. 

(b) Write the overall order of reaction. 

(c) Out of steps (I) and (II), which one is rate determining step?

Answer 1

The reactions given are as follows: 

2H₂O_{2\(\frac{I^-}{\text{alkialine medium}}\to\)}2H₂O+O₂     

H₂O₂+I^-→H₂O+IO^-(slow)    (i)

H₂O₂+IO^-→H₂O+I^-+O₂   (fast)  (ii)

(a) To find the rate expression, we consider rate determining step, which is step (I) for this reaction. Then according to the rate law,

Rate=k[H₂O₂][I^-]

(b) Since, two reagents are involved in the rate-limiting step, thus overall rate of reaction is proportional to the concentration of those reagents, that is, 2.

(c) The slowest step in this reaction is called the rate-determining step, that is step (I).