It's a combustion.

Combustions are part of what class of chemical reactions?

Combustions are oxidations.

This reaction produces heat. It is an ... reaction.

exothermic

The colorless gas obtained is sulfur dioxide. Give its chemical formula!

SO₂.

What is the meaning of the yellow color of bromothymol?

It means that SO₂ reacts with water to form an acid.

That acid is sulfurous acid. What is its formula? Describe it!!

H₂SO₃. It is a colorless and water-soluble substance.

Write down the equations of the two observed reactions!

S₈+8O₂→ 8SO₂ SO₂+H₂O→ H₂SO₃