4 K2Cr2O7 (aq) → 4 K2CrO4 (aq) + 2 Cr2O3 (s) + 3 O2 (g)
This is an oxidation-reduction (redox) reaction:
4 CrVI + 12 e- → 4 CrIII (reduction)
6 O-II - 12 e- → 6 O0 (oxidation)
K2Cr2O7 is an oxidizing agent, K2Cr2O7 is a reducing agent.
This is a precipitation reaction: Cr2O3 is the formed precipitate.
This is a gas evolution reaction, O2 is the formed gas.