定义Definition
三氧化硫 SO₃ 是硫的最高价氧化物，硫为 +6 价。气态 SO₃ 为平面三角形分子；常温下为无色易挥发的液体或固体。它是强酸性氧化物，与水剧烈反应生成硫酸。
Sulfur trioxide, SO₃, is the highest oxide of sulfur, with sulfur in oxidation state +6. Gaseous SO₃ is a trigonal planar molecule; at room temperature it is a colourless, volatile liquid or solid. It is a strongly acidic oxide that reacts violently with water to form sulfuric acid.
制备与接触法Production in the Contact process
工业上在 V₂O₅ 催化下，约 450 °C、1–2 atm 使 SO₂ 与 O₂ 反应：2SO₂ + O₂ ⇌ 2SO₃，ΔH = −197 kJ mol⁻¹。生成的 SO₃ 不直接通入水，因为反应放热过多会形成难以吸收的硫酸酸雾，而是用 98% 浓硫酸吸收生成发烟硫酸 H₂S₂O₇，再加水稀释得硫酸。
Industrially SO₂ and O₂ react over V₂O₅ at about 450 °C and 1–2 atm: 2SO₂ + O₂ ⇌ 2SO₃, ΔH = −197 kJ mol⁻¹. The SO₃ is not passed into water, because the violent heat release forms an acid mist that is hard to absorb; instead it is absorbed in 98% sulfuric acid to give oleum, H₂S₂O₇, which is then diluted.
性质Properties
SO₃ 与水反应：SO₃ + H₂O → H₂SO₄，强烈放热；与碱性氧化物反应生成硫酸盐，如 CaO + SO₃ → CaSO₄。它是强氧化剂和强脱水剂，对皮肤和呼吸道有严重腐蚀性。
SO₃ reacts with water, SO₃ + H₂O → H₂SO₄, very exothermically, and with basic oxides to form sulfates, e.g. CaO + SO₃ → CaSO₄. It is a strong oxidising and dehydrating agent and severely corrosive to skin and airways.
化学性质Chemical properties
与水反应：SO₃ + H₂O → H₂SO₄
With water: SO₃ + H₂O → H₂SO₄
被浓硫酸吸收：SO₃ + H₂SO₄ → H₂S₂O₇
Absorbed by concentrated sulfuric acid: SO₃ + H₂SO₄ → H₂S₂O₇
与碱性氧化物反应：MgO + SO₃ → MgSO₄
With basic oxides: MgO + SO₃ → MgSO₄
年表Timeline
- 1831
菲利普斯取得接触法专利
Phillips patents the Contact process
- 1915
巴斯夫开始用五氧化二钒作接触法催化剂
BASF begins using vanadium(V) oxide as the Contact process catalyst