The chemical equation for the reaction of sulfur and oxygen to form sulfur trioxide is:

S (s) + 3/2 O₂ (g) → SO₃ (g)

Here's the breakdown:

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

* O₂ (g): Oxygen in its gaseous state.

* SO₃ (g): Sulfur trioxide in its gaseous state.

* 3/2: This fraction indicates that 3 moles of oxygen molecules are needed for the reaction to occur.

Important Note: This reaction actually occurs in two steps:

1. S (s) + O₂ (g) → SO₂ (g) (Formation of sulfur dioxide)

2. 2 SO₂ (g) + O₂ (g) → 2 SO₃ (g) (Oxidation of sulfur dioxide to sulfur trioxide)

The overall equation combines these two steps.