3 C (s) + 2 K2Cr2O7 (aq) + H2O (l) → 2 Cr2O3 (s) + K2CO3 (aq) + 2 KHCO3 (aq)
This is an oxidation-reduction (redox) reaction:
3 C0 - 12 e- → 3 CIV (oxidation)
4 CrVI + 12 e- → 4 CrIII (reduction)
C is a reducing agent, K2Cr2O7 is an oxidizing agent.