(FeOH)3 + 3 H2 + 3 O2 → 3 Fe(OH)3
This is an oxidation-reduction (redox) reaction:
6 H0 - 6 e- → 6 HI (oxidation)
3 FeI - 6 e- → 3 FeIII (oxidation)
6 O0 + 12 e- → 6 O-II (reduction)
H2 is a reducing agent, (FeOH)3 is a reducing agent, O2 is an oxidizing agent.