A clock reaction is commonly used to demonstrate principles of chemical kinetics. In a clock reaction, an initially colorless solution changes color at a precise time during the course of the reaction. One such clock reaction is based on a reaction between S2O82– and I–. The rate law was determined to be rate = k [ S2O82–] [I–]. The following mechanism has been proposed for the reaction. Predict whether the steps are fast or slow based on the overall rate law.

A clock reaction is commonly used to demonstrate principles of chemical kinetics. In a clock reaction, an initially colorless solution changes color at a precise time during the course of the reaction. One such clock reaction is based on a reaction between S₂O8^2– and I^–. The rate law was determined to be rate = k [ S₂O₈^2–] [I^–]. The following mechanism has been proposed for the reaction. Predict whether the steps are fast or slow based on the overall rate law.

S₂O₈^2–+ I^– yield  IS₂O₈^3–  fast or slow

IS₂O₈^3– yield 2 SO₄^2– + I⁺  fast or slow

I⁺+ I^– yield I₂                          fast or slow

I₂+ I^– yield I₃^–                         fast or slow