H₂S Chemistry

In the year 1777, a German and Swedish Pomeranian pharmaceutical chemist Carl Wilhelm Scheele discovered the chemical composition of hydrogen sulfide (H2S).

H2S chemical name is hydrogen sulfide. It is made of hydrogen and sulfur (H2 and S, respectively). The symbol of hydrogen sulfide is H2S. 

H2S is a colourless chalcogen hydride gas with the prevalent foul smell of rotten eggs. It is a poisonous, corrosive, and flammable gas. 

Every now and again, hydrogen sulfide is set up by the microbial breakdown of natural (organic) matter without oxygen gas, as in bogs and sewers. This interaction is usually called anaerobic absorption, which is performed by sulfate-reducing microorganisms.

On this page, we will understand more about hydrogen sulfide, its preparation, properties, and uses in detail.

Do You Know?

The  British English spelling of the H2S compound name is hydrogen sulphide; however, this spelling is not accepted by the International Union of Pure and Applied Chemistry (in short, IUPAC) or the Royal Society of Chemistry.

Hydrogen Sulfide Properties

Hydrogen sulfide is an exceptionally harmful and combustible, dull gas with a trademark scent of spoiled eggs. It is utilized in the assembling of synthetic compounds, in metallurgy, and as an insightful reagent. It is heavier than air and will in general collect at the lower part of inadequately ventilated spaces. Albeit impactful from the start, it rapidly stifles the feeling of smell. 

Hydrogen sulfide happens normally in rough oil, petroleum gas, volcanic gases, and underground aquifers. It can likewise result from the bacterial breakdown of natural matter. It is likewise created by human and creature squanders. 

Hydrogen sulfide is utilized in the production of synthetic compounds, in metallurgy, and as an analytical reagent. A few properties of H2S compound name are as follows:

Properties of H2S Compound Name


Corresponding Value

Chemical Formula of Hydrogen Sulfide

H2S (hydrogen sulphur)


Dihydrogen monosulfide

Sewer gas

Dihydrogen sulfide

Sour gas


Sulfur hydride

Hydrogen sulfide chemical structure



Colourless gas


Rotten eggs

Boiling point



-213 K

Melting point



-191 K

Average molar mass

34.08 g/mol 


Sulfur - sulfur compounds

Solubility in water

4 g/dm3 at 20 °C

Vapour pressure

1740 kPa (at 21 °C)

Acidity (pKa) 


Conjugate acid


Conjugate base


Refractive index (nD)

1.000644 (0 °C)

Magnetic susceptibility 

- 25.5·10−6 cm3/mol

Hydrogen Sulfide Structure

Printing group


Molecular shape 


Dipole moment

0.97 D

Hydrogen Sulfide Thermochemistry

Thermal heat capacity

1.003 J K−1  g−1

Standard molar entropy (So298 at 298 K

206 J mol−1 K−1

Std enthalpy of

formation (ΔfH298)

- 21 kJ mol−1

Critical temperature

373.3 K

100.2 °C

212.3 °F

Critical pressure

8.97 MPa 

8.97 bar

88.5 atm

1301 psi

Critical volume

98 cm3/mol

0.00288 m3/kg

1.48 ft3/slug

0.0461 ft3/lb


44.16 mol/m3

1.505 kg/m3

0.00292 slug/ft3

61.95 lb/ft3

Hydrogen Sulfide Hazards

Hydrogen sulfide is somewhat denser than air; a combination of H2S and air can be explosive. 

The explosive properties of Hydrogen Sulfur (or if we write the chemical formula of hydrogen sulphide, it is  H2S) are as follows:

Main Dangers

Flammable and Highly Toxic

EU (European classification)


R phases




S phases








Flash point

−  82.4 °C 

− 116.3 °F

190.8 K

Explosive percentage

4.3 - 4.6 %

Autoignition temperature

232 °C 

450 °F

505 K

Lethal Dose LD50 (median concentration)

444 ppm (rat, 4 hr)

634 ppm (mouse, 1 hr)

673 ppm (mouse, 1 hr)

713 ppm (rat, 1 hr)

Lethal concentration LC50

600 ppm (human, 30 min)

800 ppm (human, 5 min)

Hydrogen Sulfide Properties

Hydrogen sulfide combines with oxygen and gives off a blue fire to frame sulfur dioxide (SO2) and water. As a rule, hydrogen sulfide goes about as a diminishing specialist, particularly within the sight of base, which structures SH

At high temperatures or within the sight of impetuses, sulfur dioxide reacts with hydrogen sulfide to frame natural sulfur and water. This response is misused in the Claus interaction, a significant mechanical strategy to discard hydrogen sulfide. 

Hydrogen sulfide is marginally solvent in water and goes about as a frail corrosive (pKa = 6.9 in 0.01 = 0.1 mol/litre arrangements at 18 °C), giving the hydrosulfide particle HS.

(likewise composed SH). 

Hydrogen sulfide and its solutions are colourless. When presented to air, it gradually oxidizes to frame natural sulfur, which isn't dissolvable in water. The sulfide anion S2 isn't found in an aqueous solution.

Hydrogen Sulfide Geometry

Hydrogen sulfide goes about as a reducing specialist. H2S Lewis structure is a combination of hydrogens and one sulfur atom. Sulfur is the focal particle and contains 2 solitary sets though both hydrogens are associated with the focal molecule with the assistance of a single bond.

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Molecular geometry


Electronic geometry




Bond angle


Total valence electrons


Formal charge


Hydrogen Sulfide Preparation

Hydrogen sulfide is most regularly acquired by its detachment from acrid gas, which is petroleum gas with a high substance of H 

2S. It can likewise be delivered by treating hydrogen with liquid natural sulfur at around 450 °C. Hydrocarbons can fill in as a wellspring of hydrogen in this process.

Sulfate-lessening (resp. sulfur-decreasing) microorganisms produce usable energy under low-oxygen conditions by utilizing sulfates (resp. basic sulfur) to oxidize natural mixtures or hydrogen; this produces hydrogen sulfide as a side-effect. 

We can produce hydrogen sulfide by treating ferrous sulfide with a strong acid like HCl in standard lab preparation. A standard lab arrangement is to treat ferrous sulfide with a solid corrosive in a Kipp generator:

FeS + 2 HCl   →     FeCl2 (l) + H2S (g)

Most metals and non-metals sulfides after exposure to  H2O liberate Hydrogen sulfide. For use in subjective inorganic investigation, thioacetamide is utilized to create H2S, the reaction is as follows: 

CH3C(S) N H2     +     H2O  (l)     →       H2S      +    CH3C(O)NH2     

Thioacetamide   Water         Hydrogen sulfide    Acetamide        

Many metal and nonmetal sulfides, for example, aluminium sulfide, phosphorus pentasulfide, silicon disulfide free hydrogen sulfide upon openness to water:

6 H2O + Al2S3       →   3 H2S + 2 Al(OH)3 

This gas is likewise delivered by warming sulfur with strong natural mixtures and by diminishing sulfurated natural mixtures with hydrogen. 

Water warmers can help the transformation of sulfate in water to hydrogen sulfide gas. This is expected to giving a warm climate reasonable to sulfur microscopic organisms and keeping up the response that connects sulfate in the water and the water warmer anode, which is generally produced using magnesium metal.

Hydrogen Sulfide Uses

The fundamental utilization of hydrogen sulfide is a forerunner to basic sulfur. A few organosulfur compounds are delivered utilizing hydrogen sulfide. These incorporate methanethiol, ethanethiol, and thioglycolic acid.

After joining with soluble base metal bases, hydrogen sulfide converts to salt hydrosulfides, for example, sodium hydrosulfide and sodium sulfide: 

H2S    +    NaOH         →      NaSH      +     H2

       Sodium Hydroxide     Sodium Hydrosulfide

On the further reaction of NaSH with NaOH, we get the following compound:

NaSH     +   NaOH   →     Na2S    +    H2

                                Sodium Sulfide

Fact: These mixtures are utilized in the paper-making industry. In particular, salts of SH− break connections among lignin and cellulose segments of mash in the Kraft process.

Reversibly sodium sulfide within the sight of acids transforms into hydrosulfides and hydrogen sulfide; this provisions hydrosulfides in natural arrangements and is used in the creation of thiophenol.

Hydrogen Sulfide Phase Diagram

Hydrogen sulfide is a gas at STP conditions. However, at low temperature and/or high pressures the gas turns to a liquid or a solid state.

The hydrogen sulfide phase diagram describes the detailed phase behaviour with changes in temperature and pressure. 

The below graph between the critical point and the triple point shows the change in the boiling point of hydrogen sulfide point with changes in pressure. Also, it shows the saturation pressure with changes in temperature:

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At the critical point, no change in state occurs when its pressure is increased or if heat is added.

Here, the triple point of a substance (hydrogen sulfide) is the temperature and pressure at which the three phases viz: gas, liquid, and solid coexist in thermodynamic equilibrium.

Hydrogen Sulfide Applications

Hydrogen sulfide is utilized to isolate deuterium oxide, or hefty water, from ordinary water through the Girdler sulfide measure. 

Researchers from the College of Exeter found that cell openness to limited quantities of hydrogen sulfide gas can forestall mitochondrial harm. 

At the point when the cell is focused on illness, proteins are brought into the cell to deliver limited quantities of hydrogen sulfide. This examination could have further ramifications on forestalling strokes, coronary illness, and arthritis.

A suspended liveliness-like state has been prompted in rodents with the utilization of hydrogen sulfide, bringing about hypothermia with an attending decrease in metabolic rate. Oxygen request was likewise diminished, along these lines ensuring against hypoxia. Furthermore, hydrogen sulfide has been appeared to diminish irritation in different situations.

FAQs (Frequently Asked Questions)

Q1: How Hydrogen Sulfide Shows Superconductivity?

Ans: On subjecting hydrogen sulfide to a pressure above 90 GPa (gigapascal), it becomes a metallic conductor of electricity. 

When this same compound is cooled below a critical temperature (373 K), at this high-pressure phase, hydrogen sulfide possesses superconductivity. 

Likewise, the basic temperature increments with pressure, going from 23 K at 100 GPa to 150 K at 200 GPa. If hydrogen sulfide is compressed at higher temperatures, cooled, the basic temperature arrives at 203 K (- 70 °C), the most noteworthy acknowledged superconducting basic temperature starting in 2015. 

By subbing a little piece of sulfur with phosphorus and utilizing significantly higher pressing factors, it has been anticipated that it could be feasible to raise the basic temperature to over 0 °C (273 K) and accomplish room-temperature superconductivity.

Q2: How We Can Determine the Molecular and Electronic Geometry of Hydrogen Sulfide?

Ans: AXN method is the most useful and the shortest method to determine electron geometry and molecular shape for H2S. However, for this, we need to make a lewis structure of H2S for using this method.

Applying AXN Method  –

A portrays the central atom.

X shows the bonded pair of electrons.

N shows the lone pair of electrons.

As per H2S lewis structure, we have:–

A - Sulfur is the central atom.

2 bonded electron pairs are attached to the central atom sulfur.

2 lone pairs are around the sulfur atom.

Therefore, the generic formula of hydrogen sulfide becomes AX2N2 for determining the molecular and electron geometry of H2S. 

So,  according to the VSEPR Shape Chart, AX2N2 tells us that the molecular geometry of H2S is bent; however, the electron geometry is tetra.