6 FeSO4 + K2Cr2O7 + 7 H2SO4 → K2SO4 + 3 Fe2[SO4]3 + Cr2[SO4]3 + 7 H2O
This is a complexation reaction: Fe2[SO4]3 andCr2[SO4]3 is the formed complex.
This is an oxidation-reduction (redox) reaction:
6 FeII - 6 e- → 6 FeIII (oxidation)
2 CrVI + 6 e- → 2 CrIII (reduction)
FeSO4 is a reducing agent, K2Cr2O7 is an oxidizing agent.