Sulfur Dioxide and Hydrogen Sulfide Reaction, SO2 + H2S = S + H2O, Balanced Equation

Sulphur Dioxide and Hydrogen Sulfide Reaction | SO2 + H2S = S + H2O Balanced Equation

Sulphur dioxide and hydrogen sulfide are gases and they react with each other in the presence of moisture to give sulphur and water as products. This reaction is a sulphur forming reaction and also a redox reaction.

Redox reaction

A reaction, which undergo oxidation and reduction in same time is defined as a redox reaction.

SO2 + H2S = S + H2O reaction

This is a redox reaction (oxidation - reduction). Sulphur atom in the sulphur dioxide molecule is reduced to sulfur while sulphur atom in the hydrogen sulphide is oxidized to sulfur. This reaction occurs in the presence of moisture. SO2 and H2S are in gaseous state and produced sulfur is given as a pale yellow solid.

  • SO2 is reduced to sulfur. Oxidation number of sulfur atom in SO2 molecule is +4. That sulfur atom is reduced to 0 oxidation state when sulfur is formed.
  • H2S is oxidized to sulfur. Sulfur atom of H2S molecule is at -2 oxidation state and it is oxidized to zero oxidation state.

Balancing the equation

Due to forming sulfur by both H2S and SO2, we follow a special method to balance this equation. Remember how to balance a redox reaction and its steps!

  • Find the oxidation numbers of each atom to find which atoms are oxidized and reduced. When finding the oxidation numbers, we see SO2 is reduced and H2S is oxidized.
  • At initial situation, there are two sulfur atoms in the left side of the equation. But right side has only one. So add one more sulfur atom to the right side.
  • Then take the oxidation number difference in oxidation and reduction. Oxidation number differences of oxidation and reduction are 2 and 4 respectively. Next exchange the differences. See the figure how exchanging is done.
  • Finally balance the H2O by checking oxygen atoms of left and right sides.

Redox reaction between hydrogen sulfide and sulphur dioxide - balanced reaction

One sulphur dioxide molecule reacts with two hydrogen sulphide molecules and produces three sulfur atoms and two water molecules.

sulphur dioxide and hydrogen sulfide reaction - SO2 + H2S

SO2 gas properties

  • Colourless
  • Acidic
  • Toxic
  • Heavier than air

H2S gas properties

  • Colurless
  • Very toxic
  • Weak Acidic
  • Heavier than air


SO2 and H2S are very toxic gases and causes harmful injuries to humans, animals and whole environment. Inhaling H2S in very small amounts is enough to cause death. H2S toxic levels are mentioned below.

Hydrogen sulfide toxicity levels

This toxicity levels of H2S and effects were taken by Safety and Health Topics / Hydrogen Sulfide at . Concentrations are expressed in ppm values. In this experiment, your should be very careful to get protected from these hazardous chemicals.

toxicity levels of hydrogen sulfide concentration and effects


what is detimental for sulfur dioxide (so2) and hydrogen sulfide

Both sulfur dioxide and hydrogen sulfide are toxic compounds and has the capability to harm people. Hydrogen sulfide is more and more danger thann sulfur dioxide

What is the oxidation number of sulfur in h2s

First identify which atom has the higher electronegativity. Sulfur and hydrogen's electronegativity values are 2.5 and 2.1 respectively. So hydrogen should have positive oxidation number and sulfur has a negative oxidation number.

We know hydrogen's only positive oxidation number is +1.

Using the oxidation number determing equation

  • (+1 * 2) + x = 0
  • x = -2

Oxidation number of sulfur in H2S is -2.

How do you find SO2 and H2S in large scale?

In petroleum refining, H2S gas forms due to removing or decreasing sulfur in fuels. Some refineries (old ones) burn H2S before releasing to the environment. When H2S burning in the O2 SO2 forms.

Is HS + SO2 a redox reaction?

Yes. H2S is oxidized to sulfur and SO2 is reduced to sulfur.

How do you identify H2S and SO2?

Both are colourless gases. Send to gases separately to two barium chloride solution.

  • In one solution, a white precipitate forms. It is BaSO3.
  • In other solution, there is no precipitate forming.

sulfur dioxide equation

Dioxide means an oxide with two oxygen atoms. Therefore chemical equation of sulfur dioxide is SO2.

Will H2S + SO2 reaction will help to reduce hydrogen sulfide environmental effects?

If H2S is produced or released from a plant in great amount, this reaction is a good way to recover H2S. But this depend availability of sulfur dioxide gas.

what is sulphur + H2O?

Sulfur does not react with water and also does not dissolve in water.

oxidation of hydrogen sulfide to sulfur dioxide

When hydrogen sulfide is heated with oxygen gas, sulfur dioxide is given as the product. Here sulfur dioxide is oxidized to sulfur dioxide.

sodium reacts with sulphur to give sodium sulphide is this a redox reaction

Oxidation number of sulfide ion in sodium sulfide is -2. Therefore, oxidation number of sulfur is changed from 0 to -2. Therefore this sodium and sulphur reaction should be a redox reaction.

water + hydrogen sulfide reaction

When hydrogen sulfide dissolve in water, a weak acidic solution is given.

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