Cr2O2−7+I−+H+→Cr3++I2+H2O
1st step: Splitting into two half reactions,
Cr2O2−7+H+→Cr3++H2O(Reductionhalfreaction); I−→I2(Oxidationhalfreaction)
2nd step: Adding hydrogen ions to the side deficient in hydrogen,
Cr2O2−7+14H+→Cr3++7H2O
3rd side: Making atoms equal on both sides,
Cr2O2−7+14H+→2Cr3++7H2O;2I−→I2
4th step: Adding electrons to the sides deficient in electrons,
Cr2O2−7+14H++6e→2Cr3++7H2O
2I−→I2+2e
5th step: Balancing electrons,
Cr2O2−7+14H++6I−→2Cr3++3I2+7H2O.