Sulfur trioxide

Sulfur trioxide
	Resonance structures
	Space-filling model
Names
	Preferred IUPAC name Sulfur trioxide
	Systematic IUPAC name Sulfonylideneoxidane
	Other names Sulfuric anhydride, Sulfur(VI) oxide
Identifiers
CAS Number	7446-11-9 ;
3D model (JSmol)	monomer: Interactive image; γ-trimer: Interactive image; α/β polymer: Interactive image; (monohydrate): Interactive image;
ChEBI	CHEBI:29384 ;
ChemSpider	23080 ;
ECHA InfoCard	100.028.361
EC Number	231-197-3;
Gmelin Reference	1448
PubChem CID	24682; 22235242 ; (hemihydrate); (monohydrate): 23035042;
RTECS number	WT4830000;
UNII	HH2O7V4LYD ;
UN number	UN 1829
CompTox Dashboard (EPA)	DTXSID1029673 ;
	InChI InChI=1S/O3S/c1-4(2)3 Key: AKEJUJNQAAGONA-UHFFFAOYSA-N ; InChI=1/O3S/c1-4(2)3 Key: AKEJUJNQAAGONA-UHFFFAOYAX; (monohydrate): InChI=1S/O3S.H2O/c1-4(2)3;/h;1H2 Key: DEUOBQUHDSDIFY-UHFFFAOYSA-N;
	SMILES monomer: O=S(=O)=O; γ-trimer: O=S0(=O)OS(=O)(=O)OS(=O)(=O)O0; α/β polymer: OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)O; (monohydrate): O.O=S(=O)=O;
Properties
Chemical formula	SO3
Molar mass	80.066 g/mol
Appearance	Colorless to white crystalline solid which will fume in air. Colorless liquid and gas.
Odor	Varies. Vapor is pungent; like sulfur dioxide. Mist is odorless.
Density	1.92 g/cm3, liquid
Melting point	16.9 °C (62.4 °F; 290.0 K)
Boiling point	45 °C (113 °F; 318 K)
Solubility in water	Reacts to give sulfuric acid
Thermochemistry
Std molar; entropy (S⦵298)	256.77 JK−1mol−1
Std enthalpy of; formation (ΔfH⦵298)	−395.7 kJ/mol
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	Highly corrosive, extremely strong dehydrating agent
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314, H335
Precautionary statements	P261, P280, P305+P351+P338, P310
NFPA 704 (fire diamond)	3 0 3 W; OX
Flash point	Non-flammable
	Lethal dose or concentration (LD, LC):
LC50 (median concentration)	rat, 4 hr 375 mg/m3
Safety data sheet (SDS)	ICSC 1202
Related compounds
Other cations	Selenium trioxide; Tellurium trioxide; Polonium trioxide
Related sulfur oxides	Sulfur monoxide; Sulfur dioxide
Related compounds	Sulfuric acid
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Sulfur trioxide (alternative spelling sulphur trioxide) is the chemical compound with the formula SO₃. It has been described as "unquestionably the most [economically] important sulfur oxide". It is prepared on an industrial scale as a precursor to sulfuric acid.

Sulfur trioxide exists in several forms: gaseous monomer, crystalline trimer, and solid polymer. Sulfur trioxide is a solid at just below room temperature with a relatively narrow liquid range. Gaseous SO₃ is the primary precursor to acid rain.