Final answer:
The chemical equation for the reaction between sulfur dioxide gas and oxygen gas to form sulfur trioxide gas is 2 SO₂(g) + O₂(g) → 2 SO₃(g), with all substances in the gaseous state.
Step-by-step explanation:
The reaction between sulfur dioxide gas and oxygen gas to form sulfur trioxide gas can be expressed as the following balanced chemical equation:
2 SO₂(g) + O₂(g) → 2 SO₃(g)
In this equation, (g) indicates that sulfur dioxide (SO₂), oxygen (O₂), and sulfur trioxide (SO₃) are all in the gaseous phase. This reaction is a fundamental step in the industrial synthesis of sulfuric acid and is exothermic, releasing energy in the form of heat.