Sulfur trioxide
From Freepedia
| Sulfur trioxide | |
|---|---|
| Other names | Sulfuric anhydride Sulfan® Sulphur trioxide |
| Molecular formula | SO3 |
| Molar mass | 80.06 g/mol |
| CAS number | [7446-11-9] |
| Density | 1.92 g/cm3 |
| Solubility (water) | Hydrolysis |
| Melting point | 16.9°C |
| Boiling point | 45°C |
| Thermodynamic data | |
| Standard enthalpy of formation ΔfH°gas | -397.77 kJ/mol |
| Standard molar entropy S°gas | 256.77 J.K–1.mol–1 |
| Heat capacity Cp,gas | 24.02 J.K–1.mol–1 |
| Safety data | |
| EU classification | Corrosive (C) |
| R-phrases | R14, R35, R37 |
| S-phrases | S1/2, S26, S30, S45 |
| Disclaimer and references | |
Sulfur trioxide (British spelling: Sulphur trioxide) has the chemical formula SO3.
Sulfur trioxide is liquid, density 1.92 g/cm3, boiling point +43.7°C, melting point +16.8°C. 3 electron pairs for VSEPR consideration
When mixed with water, it produces sulfuric acid (H2SO4):
- SO3 + H2O = H2SO4 (+ 88 kJ)
which, upon heating, boils at ~290°C, and decomposes back into sulfur trioxide and water at 340°C.
Sulfur trioxide is prepared by the two-stage pyrolysis of sodium hydrogen sulfate:
- NaHSO4 → Na2S2O7 + H2O
- Na2S2O7 → Na2SO4 + SO3
This method will work for other metal bisulfates, the controlling factor being the stability of the intermediate disulfate salt.
