What is a Sulfur trioxide (SO₃)?

Sulfur trioxide (SO₃) is a highly reactive inorganic compound composed of sulfur and oxygen. At room temperature, it can exist as a white crystalline solid or a fuming liquid. It reacts violently with water, releasing heat and forming concentrated sulfuric acid. Industrially, SO₃ is produced via the contact process by oxidizing sulfur dioxide (SO₂). It is mainly used in the large-scale production of sulfuric acid (H₂SO₄), one of the most essential chemicals in industry. Sulfuric acid is crucial for fertilizers, explosives, dyes, synthetic fibers, and ore processing.

SO₃ is extremely hygroscopic and reacts with moisture in the air, often producing white fumes. Due to its high corrosiveness, it must be handled with acid-resistant equipment and proper protective gear. Environmentally, SO₃ contributes to acid rain. It forms from SO₂ oxidation in the atmosphere and reacts with water to produce sulfuric acid, which falls with rain. Therefore, strict emission controls are enforced in many countries.

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