Hydrogen sulfide
Systematic name Hydrogen sulfide
Other names	Dihydrogen monosulfide Dihydrogen sulfide Sewer gas Sulfane Sulfurated hydrogen Sulfureted hydrogen Sulfuretted hydrogen Sulfur hydride Hydrosulfuric acid Hydrothionic acid Thiohydroxic acid Sulfhydric acid
Identifiers
CAS number	7783-06-4
PubChem	402
EC number	231-977-3
KEGG	C00283
MeSH	Hydrogen+sulfide
ChEBI	CHEBI:16136
RTECS number	MX1225000
SMILES	[H]S[H]
InChI InChI=1/H2S/h1H2
Beilstein Reference	3535004
Gmelin Reference	303
3DMet	B01206
Properties
Molecular formula	H2S
Molar mass	34.08 g mol-1
Appearance	Colorless gas
Odor	Rotten eggs
Density	1.363 g dm−3
Melting point	−82 °C, 191 K, -116 °F
Boiling point
Solubility in water	4 g dm−3 (at 20 °C)
Vapor pressure	1740 kPa (at 21 °C)
Acidity (pKa)	7.0
Magnetic susceptibility (χ)	−25.5·10−6 cm3/mol
Refractive index (nD)	1.000644 (0 °C)
Structure
Point group	C2v
Molecular shape	Bent
Dipole moment	0.97 D
Thermochemistry
Std enthalpy of formation ΔfHo298	−21 kJ mol−1
Standard molar entropy So298	206 J mol−1 K−1
Specific heat capacity, C	1.003 J K−1 g−1
Hazards
EU classification	F+ T+ N
Main hazards	Flammable and highly toxic
NFPA 704	4 4 0
R-phrases	R12, R26, R50
S-phrases	(S1/2), S9, S16, S36, S38, S45, S61
Explosive limits	4.3–46%
U.S. Permissible exposure limit (PEL)	C 20 ppm; 50 ppm [10-minute maximum peak]
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Hydrogen sulfide (British English: hydrogen sulphide) is the chemical compound with the formula H₂S, is a colorless, toxic, flammable gas that is responsible for the foul smell of rotten eggs and flatulence. It often results when bacteria break down organic matter if there is no oxygen. This happens in swamps, and sewers (alongside the process of anaerobic digestion). It also happens in volcanic gases, natural gas and some well waters. This is the smell that people often think to be that of sulfur. But sulfur itself does not smell.