The reaction of sulfur with oxygen to form sulfur trioxide is:

2 S (s) + 3 O₂ (g) → 2 SO₃ (g)

Here's what the equation represents:

* S (s): Sulfur in its solid state (s)

* O₂ (g): Oxygen gas (g)

* SO₃ (g): Sulfur trioxide gas (g)

This reaction is a combustion reaction where sulfur reacts with oxygen to produce sulfur trioxide. The coefficients in the balanced equation (2, 3, and 2) ensure that the number of atoms of each element is the same on both sides of the equation.