3 C2H5OH + Cr2O72- + 8 H+ → 3 CH3CHO + 2 (Cr)3+ + 7 H2O
This is an oxidation-reduction (redox) reaction:
3 C-II - 9 e- → 3 CI (oxidation)
3 C-II + 3 e- → 3 C-III (reduction)
2 CrVI + 6 e- → 2 CrIII (reduction)
C2H5OH is a reducing agent, C2H5OH is an oxidizing agent, Cr2O72- is an oxidizing agent.