You're absolutely right! The reaction you're describing is the formation of sulfur trioxide from sulfur dioxide and oxygen:

2 SO₂ (g) + O₂ (g) ⇌ 2 SO₃ (g)

This is an important reaction in the production of sulfuric acid.

The reverse reaction is the decomposition of sulfur trioxide back into sulfur dioxide and oxygen:

2 SO₃ (g) ⇌ 2 SO₂ (g) + O₂ (g)

This reaction can be driven by various factors like:

* Heat: Increasing temperature favors the endothermic reverse reaction.

* Pressure: Decreasing pressure favors the reverse reaction, as it has more moles of gas on the product side.

* Catalyst: A catalyst can speed up both the forward and reverse reactions.

Let me know if you have any other questions!