Question

Is 2H⁺+H₂O₂+2I^- ---> 2H₂O+I₂ unimolecular, bimolecular or termolecular? Explain.

Answer 1

The given reaction

2 I- + H2O2 + 2 H+ ---> I2 + 2 H2O

The elementary steps

Step 1 is the slowest step and molecularity is bimolecular

H2O2 + I- -----> H2O + OI-

Step 2 is fast and molecularity is bimolecular

H+ + OI- - - - - - > HOI

Step 3 is fast and molecularity is termolecular

HOI + H+ + I- - - - - > I2 + H2O

Sum of all steps gives

2 I- + H2O2 + 2 H+ ---> I2 + 2 H2O

Step 1 is the rate determining step and it is bimolecular.

reaction intermediates are HOI and OI-

Rate law = k [I-] [H2O2]