The key difference between H2S and SO2 is that H2S has the smell of a rotten egg, whereas SO2 has the smell of a burnt match.
Both H2S and SO2 are gaseous compounds at room temperature. These compounds contain sulfur atoms. H2S is a hydride of sulfur while SO2 is an oxide of sulfur. Moreover, both these gases have a pungent odour.
What is H2S?
H2S is hydrogen sulfide. It is a gas at room temperature, having the smell of a rotten egg. Therefore, it has a pungent and irritating odour. This gas is highly poisonous. Moreover, it is corrosive and flammable as well. Therefore, we need to handle it carefully. The molar mass of H2S is 38.09 g/mol. It appears as a colourless gas.
The H2S gas is slightly denser than normal atmospheric air. However, a mixture of air and H2S can cause explosive reactions. Furthermore, this gas burns in air with a blue flame upon the presence of oxygen gas. This reaction gives SO2 and water. Generally, H2S gas acts as a reducing agent because it can undergo only oxidation since the sulfur atom in this compound is in its least oxidation state (cannot be further reduced).
We can use H2S to get elemental sulfur. The reaction between H2S and SO2 in the presence of a catalyst and high temperature gives elemental sulfur and water. This is an important method to dispose of H2S. Moreover, H2S is slightly water-soluble and upon dissolution, it can form a weak acid.
H2S can react with metals and forms metal sulfides. These metal sulfides are water-insoluble compounds having dark colours. For example, we can use a lead(II) acetate applied paper to detect H2S evolving from a sample because lead in the paper can react with H2S forming black colour lead sulfide.
What is SO2?
SO2 is sulfur dioxide. It is a toxic gas that is colourless and has the smell of burnt matches. In nature, this gas is evolved from volcanic eruptions. The molar mass of this gas is 64.8 g/mol. It is slightly water-soluble and upon dissolution, it forms sulfurous acid. Moreover, this gas can undergo both oxidation and reduction reactions because the sulfur atom in this molecule is in between least and highest oxidation states that a sulfur atom can show. Therefore, SO2 can act as both a reducing agent and as an oxidizing agent.
When considering the production of SO2, it is primarily produced from sulfuric acid manufacturing. Moreover, SO2 gas is the product of the burning sulfur (or burning material that contain sulfur). In addition, this gas is a byproduct of the manufacture of calcium silicate cement. We can produce SO2 from the reaction of an aqueous base with SO2.
What is the Difference Between H2S and SO2?
Both H2S and SO2 are gaseous compounds at room temperature. The key difference between H2S and SO2 is that H2S has the smell of a rotten egg, whereas SO2 has the smell of a burnt match. Therefore, both these gases have a pungent odour. Besides, we can produce H2S via the separation of sour gas while we can produce SO2 as a byproduct from sulfuric acid manufacturing.
When considering the uses of these gases, we can use H2S for the production of elemental sulfur, in qualitative analysis of metals, as a precursor to metal sulfides, etc., whereas SO2 is useful as a precursor for sulfuric acid, as a food additive, as a reducing agent, in winemaking, etc.
Below infographic summarizes the difference between H2S and SO2.
Summary – H2S vs SO2
Both H2S and SO2 are gaseous compounds at room temperature. The key difference between H2S and SO2 is that H2S has the smell of a rotten egg, whereas SO2 has the smell of a burnt match.
1. Helmenstine, Anne Marie, “10 Interesting Sulfur Facts.” ThoughtCo, Oct. 8, 2019, Available here.