Will this reaction occur? I was studying reductive behaviour of $\ce{H2S}$. So, there is one reaction in my textbook.

$$\ce{3H2S + K2Cr2O7 + 4H2SO4 -&gt; 3S + Cr2(SO4)3 + K2SO4 + 7H2O}$$

This reaction oxidizes $\ce{S^2-}$ to $\ce{S}$. But I thought why not $\ce{SO2}$?

$$\ce{H2S + K2Cr2O7 + 4H2SO4 -&gt; SO2 + Cr2(SO4)3 + K2SO4 + 5H2O}$$

The reaction seems stoichiometrically plausible, but this reaction must need highly concentrated oxidants. I know the 1st reaction happens at low concentration of $\ce{H2SO4}$. Maybe then using high concentrated $\ce{H2SO4}$ would do the work for 2nd one.

I am not sure, though I am confident that the 2nd reaction will happen. What do you think?
But I thought why not $\ce{SO2}$


While the reaction is stechiometrically correct, it is hard to perform.


In excess of $\ce{H2S}$ sulfur will be produced.
In excess of oxidant sulfate will be produced.


And exact balance is impossible to achieve.

That said, $\ce{SO2}$ reacts with  $\ce{H2S}$ finally producing sulfur. This reaction, just like many inorganic reactions, is an unholy mess of many different processes with many products obtained simulationaly and the only way to produce understandable and reproduceable results is to simplify the situation. One of the way to simplify the situation is to use a vast excess of one of the reagents.