Earlier a laboratory exercise was proposed in which the students
use the initial rates method based on the clock reaction
approach to deduce the rate law and propose a reaction mechanism
for the oxidation of iodide by iron(III) ions.1 Here an
extension of that exercise is reported in which the students determine
the dependence of the reaction rate on ionic strength
and temperature using the same approach. The first study
further supports the proposed mechanism (eq 6) and identifies
the reaction between FeI2+ and I− ions as the rate-determining
step, whereas the latter study reveals the activation quantities
Ea, Δ⧧H, and Δ⧧S for the overall reaction of the first two steps
of the mechanism.