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Hydrogen sulfide facts for kids

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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
CAS number 7783-06-4
PubChem 402
EC number 231-977-3
KEGG C00283
MeSH Hydrogen+sulfide
RTECS number MX1225000
Beilstein Reference 3535004
Gmelin Reference 303
3DMet B01206
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

−60 °C, 213 K, -76 °F

Solubility in water 4 g dm−3 (at 20 °C)
Vapor pressure 1740 kPa (at 21 °C)
Acidity (pKa) 7.0
−25.5·10−6 cm3/mol
Refractive index (nD) 1.000644 (0 °C)
Molecular shape Bent
Dipole moment 0.97 D
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
EU classification Flammable F+ Very Toxic T+ Dangerous for the Environment (Nature) N
Main hazards Flammable and highly toxic
NFPA 704

NFPA 704.svg

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.

Hydrogen sulfide is also known as sulfane, sulfur hydride, sour gas, sulfurated hydrogen, hydrosulfuric acid, sewer gas and stink damp. IUPAC accepts the names "hydrogen sulfide" and "sulfane". When people speak of more complicated compounds they always use the term "sulfane".


Deposit from hydrogen sulphide
Deposit of sulfur on a rock, caused by volcanic gases containing hydrogen sulfide

Small amounts of hydrogen sulfide can be found in crude petroleum. Sour natural gas can contain up to 28%. But, sour natural gas must be cleaned before it can enter a long distance pipeline. Pipelines limit hydrogen sulfide to 3 grains per thousand cubic feet of natural gas. Volcanoes and hot springs give off some H2S, where it probably is made by the hydrolysis of sulfide minerals, i.e. MS + H2O to give MO + H2S.

Normal average concentration in clean air is about 0.0001-0.0002 ppm.


Hydrogen sulfide is a highly toxic and flammable gas. Because it is heavier than air it tends to accumulate at the bottom of poorly ventilated spaces.


Hydrogen sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is most affected. The toxicity of H2S is comparable with that of hydrogen cyanide.

  • "Hydrogen Sulfide", Committee on Medical and Biological Effects of Environmental Pollutants, University Park Press, 1979, Baltimore. ISBN: 0-8391-0127-9

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See also

Kids robot.svg In Spanish: Ácido sulfhídrico para niños

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