28 H2SO4 + 7 K2Cr2O7 + 3 C3H5(OH)3 → 40 H2O + 9 CO2 + 7 K2SO4 + 7 Cr2(SO4)3
This is an oxidation-reduction (redox) reaction:
9 C-2/3 - 42 e- → 9 CIV (oxidation)
14 CrVI + 42 e- → 14 CrIII (reduction)
C3H5(OH)3 is a reducing agent, K2Cr2O7 is an oxidizing agent.