Chemical, physical and thermal properties of hydrogen sulfide, H2S, also called hydrosulfuric acid, sewer gas and stink damp. Phase diagram included.

Hydrogen sulfide, H2S, is ahighly toxic and flammable, colorless gas with a characteristic odor of rotten eggs. It is used in the manufacture of chemicals, in metallurgy, and as an analytical reagent. It is heavier than air and tends to accumulate at the bottom of poorly ventilated spaces. Although very pungent at first, it quickly deadens the sense of smell.

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Hydrogen sulfide occurs naturally in crude petroleum, natural gas, volcanic gases, and hot springs. It can also result from bacterial breakdown of organic matter. It is also produced by human and animal wastes.

Hydrogen sulfide is used in the manufacture of chemicals, in metallurgy, and as an analytical reagent.

The phase diagram of hydrogen sulfide is shown below the table.

Chemical, physical and thermal properties of hydrogen sulfide:Values are given for gas phase at 25oC /77oF / 298 K and 1 bara, if not other phase, temperature or pressure given.

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Property Value Unit Value Unit Value Unit Value Unit
Autoignition temperature 505 K 232 °C 450 °F
Boiling Point 213.6 K -59.55 °C -75.2 °F
Critical density 10.2 mol/dm3 348 kg/m3 0.675 slug/ft3 21.7 lb/ft3
Critical pressure 8.97 MPa=MN/m2 89.7 bar 88.5 atm 1301 psi=lbf/in2
Critical temperature 373.3 K 100.2 °C 212.3 °F
Critical volume 98 cm3/mol 0.00288 m3/kg 1.48 ft3/slug 0.0461 ft3/lb
Density(gas) 44.16 mol/m3 1.505 kg/m3 0.00292 slug/ft3 0.0940 lb/ft3
Density (liquid) at -121.9 °F/-85.5°C 29116 mol/m3 992.3 kg/m3 1.925 slug/ft3 61.95 lb/ft3
Density (liquid) at -76 °F/-60°C 26877 mol/m3 916.0 kg/m3 1.777 slug/ft3 57.18 lb/ft3
Flammable, gas and liquid yes
Flash point 480 K 207 °C 405 °F
Gas constant, individual - R 244.0 J/kg K 0.06777 Wh/(kg K) 1459 45.34
Gibbs free energy of formation(gas) -34 kJ/mol -998 kJ/kg -429 Btu/lb
Heat (enthalpy) of formation(gas) -20.6 kJ/mol -604 kJ/kg -260 Btu/lb
Heat (enthalpy) of sublimation,at -145°F/-98°C 25.4 kJ/mol 745 kJ/kg 320 Btu/lb
Heat (enthalpy) of evaporationat-100°F/-73°C 20.00 kJ/mol 353.4 kJ/kg 151.93 Btu/lb
Heat capacity, Cp (gas) 34.6 J/mol K 1.01 kJ/kg K 0.242 Btu/lb°F or cal/g K
Specific heat capacity, Cp (liquid) at 20 bara 76.5 J/mol K 2.24 kJ/kg K 0.536 Btu/lb°F or cal/g K
Specific heat capacity, Cv (gas) 26.0 J/mol K 0.76 kJ/kg K 0.182 Btu/lb°F or cal/g K
Specific heat capacity, Cv (liquid) at 20 bara 37.0 J/mol K 1.09 kJ/kg K 0.259 Btu/lb°F or cal/g K
Ionization potential 10.46 eV
Melting point 187.66 K -85.5 °C -121.9 °F
Molecular Weight 34.081 g/mol 0.07514 lb/mol
Solubilityin water, at 25°C 4 mg/ml
Sound velocityin gas 309 m/s 1014 ft/s 692 mi/h
Sound velocity in liquid at 20 bara 836 m/s 2742 ft/s 1873 mi/h
Specific Gravity(gas) (relativ to air) 1.19
Specific Gravity (liquid) (relativ to water) 0.92
Specific Heat Ratio(gas) - CP/CV 1.33
Specific Heat Ratio (liquid) - CP/CV at 20 bara 2.07
Specific Volume (gas) 0.023 m3/mol 0.66 m3/kg 342.44 ft3/slug 10.64 ft3/lb
Specific Volume (liquid) at -121.9 °F/-85.5°C 0.0000343 m3/mol 0.00101 m3/kg 0.519 ft3/slug 0.0161 ft3/lb
Standard molar entropy, S° (gas) 206 J/mol K 6.04 kJ/kg K 1.44 Btu/lb °F
Surface tensionat 257°F/125°C 58.1 dynes/cm 0.0581 N/m
Thermal Conductivity 0.018 W/m °C 0.010400 Btu/hr ft °F
Triple pointpressure 0.0233 MPa=MN/m2 0.233 bar 0.230 atm 3.38 psi=lbf/in2
Triple point temperature 187.63 K -85.5 °C -121.94 °F
Vapor (saturation) pressure 2.0262 MPa=MN/m2 15200.0 mm Hg 19.9971 atm 293.88 psi=lbf/in2
Viscosity, dynamic (absolute) 0.013 cP 8.6 0.27
Viscosity, kinematic 8.505 cSt 91.5

See more about atmospheric pressure, and STP - Standard Temperature and Pressure & NTP - Normal Temperature and Pressure, as well as Thermophysical properties of: Acetone, Acetylene, Air, Ammonia, Argon, Benzene, Butane, Carbon dioxide, Carbon monoxide, Ethane, Ethanol, Ethylene, Helium, Hydrogen, Methane, Methanol, Nitrogen, Oxygen, Pentane, Propane, Toluene, Water and Heavy water, D2O.

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Hydrogen sulfide is a gas at standard conditions. However, at low temperature and/or high pressures the gas becomes a liquid or a solid.

The hydrogen sulfide phase diagram shows the phase behavior with changes in temperature and pressure. The curve between the critical point and the triple point shows the hydrogen sulfide boiling point with changes in pressure. It also shows the saturation pressure with changes in temperature.


At the critical point there is no change of state when pressure is increased or if heat is added.

See more: How Do You Solve This Inequality: 3B – 7 ≪ 32, Solve This Inequality: 3B

The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.