The decomposition of hydrogen peroxide is given by the following reaction:2 H2O2(aq) → 2 H2O(l) + O2(g)In the presence of KI the reaction is thought to occur by the following mechanism:Step 1: H2O2 + I- → H2O + IO-Step 2: IO- + H2O2 → H2O + O2 + I-What is the role of I- in this mechanism?

Role of I⁻ in this mechanism is a catalyst

Explanation:

The decomposition of hydrogen peroxide is catalyzed as shown below.  

The catalyzed reaction is thought to proceed by a two-step mechanism:  

                            H₂O₂+ I⁻ → H₂O + IO⁻              (slow)  

                      IO⁻ + H₂O₂   → I⁻ + H₂O + H₂O₂     (fast)

The rate law for the overall process Rate=k [H₂O₂][I⁻ ] according to slow elementary step. However, it’s not consumed in the reaction and therefore changing its concentration does not impact rate. Its behavior as a catalyst will impact the value for k. This is often designated with k’ so we can write the rate law as: Rate=k’ [H₂O₂]

it forms an anion that has a larger radius. anions have a negative charge and are larger than the original atom.