This is the balanced chemical equation for the reaction between sulfur dioxide (SO2), potassium dichromate (K2Cr2O7), and sulfuric acid (H2SO4) to form potassium sulfate (K2SO4), chromium (III) sulfate (Cr2(SO4)3), and water (H2O):

3 SO2 + K2Cr2O7 + 7 H2SO4 → K2SO4 + Cr2(SO4)3 + 7 H2O