Question

How would we represent the reaction of `SO_2` with `K_2Cr_2O_7` to give `SO_3`?

Answer 1

We would assume that the sulfur dioxide is oxidized to sulfur trioxide.

Explanation:

`stackrel(IV+)"SO"_2 +H_2O rarr stackrel(VI+)"SO"_3 +2H^(+) +2e^(-)` `(1)`

And dichromate is reduced to chromic ion......:

`Cr_2O_7^(2-) +14H^(+) + 6e^(-) rarr 2Cr^(3+) + 7H_2O` `(2)`

And we take `3xx(1)+(2)` to eliminate the electrons:

`Cr_2O_7^(2-) +8H^(+) + 3SO_2 rarr 2Cr^(3+) + 3SO_3 + 4H_2O`

Are charge and mass balanced? If the answer is no then we cannot accept the reaction. Industrially, the oxidant is oxygen gas. I do not know if the reaction would proceed as written.