2 HI-I + Fe2III(SO4)3 I20 + 2 FeIISO4 + H2SO4

This is an oxidation-reduction (redox) reaction:

2 I-I - 2 e- 2 I0 (oxidation)

2 FeIII + 2 e- 2 FeII (reduction)

Change the oxidation states