Question

Classify the reaction between ${\mathrm{H}}_2\mathrm{S}$ and ${\mathrm{SO}}_2$ that leads to the formation of sulfur at the site of a volcanic eruption.

Short answer

It's a redox and precipitation reaction.

Step-by-step solution

Write the Chemical Equation

To classify the reaction, first write the balanced chemical equation. The reaction between hydrogen sulfide ${\mathrm{H}}_2\mathrm{S}$ and sulfur dioxide ${\mathrm{SO}}_2$ can be expressed as follows: $$2{\mathrm{H}}_2\mathrm{S}+{\mathrm{SO}}_2\to 3\mathrm{S}+2{\mathrm{H}}_2\mathrm{O}$$ This shows that hydrogen sulfide reacts with sulfur dioxide to form sulfur and water.

Identify the Type of Reaction

Examine the reactants and products to classify the reaction type. Notice that sulfur dioxide ${\mathrm{SO}}_2$ is reduced to elemental sulfur $\mathrm{S}$, and hydrogen sulfide ${\mathrm{H}}_2\mathrm{S}$ is oxidized to water ${\mathrm{H}}_2\mathrm{O}$. This indicates that electrons are transferred, making it an oxidation-reduction (redox) reaction.

Further Classification (Precipitation)

In a volcanic eruption's conditions, sulfur forms as a solid precipitate from the gaseous reactants ${\mathrm{H}}_2\mathrm{S}$ and ${\mathrm{SO}}_2$. This aspect also allows the reaction to be classified under precipitation reactions, as a solid product (sulfur) is formed.

Key concepts

Chemical Equation

A chemical equation represents a chemical reaction using symbols and formulas. It provides a quick overview of what happens in a chemical reaction. For the reaction between hydrogen sulfide ${\mathrm{H}}_2\mathrm{S}$ and sulfur dioxide ${\mathrm{SO}}_2$, the chemical equation is:$$2{\mathrm{H}}_2\mathrm{S}+{\mathrm{SO}}_2\to 3\mathrm{S}+2{\mathrm{H}}_2\mathrm{O}$$This equation tells us that:

• Two molecules of hydrogen sulfide react with one molecule of sulfur dioxide.
• They produce three atoms of sulfur and two molecules of water.

Understanding the chemical equation is crucial because it shows how substances interact and transform in a reaction. It also ensures that the reaction complies with the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.

Reaction Classification

Classifying chemical reactions helps in understanding the underlying chemical processes. The reaction between ${\mathrm{H}}_2\mathrm{S}$ and ${\mathrm{SO}}_2$ is an example of an oxidation-reduction reaction, often called a redox reaction. In redox reactions, one substance loses electrons (oxidation) while another gains electrons (reduction).In our reaction:

• ${\mathrm{SO}}_2$ is reduced to sulfur $\mathrm{S}$, meaning it gains electrons.
• Simultaneously, ${\mathrm{H}}_2\mathrm{S}$ is oxidized to water ${\mathrm{H}}_2\mathrm{O}$, indicating it loses electrons.

By identifying the substances undergoing oxidation and reduction, students improve their grasp of how electrons drive chemical transformations. Redox reactions are common in everyday life, playing a vital role in processes like combustion, metabolism, and even battery operation.

Precipitation Reactions

Precipitation reactions involve the formation of a solid from a solution during a chemical reaction. In the given context, during volcanic eruptions, the gaseous reactants ${\mathrm{H}}_2\mathrm{S}$ and ${\mathrm{SO}}_2$ come together to form solid sulfur. This solid formation fits the criteria of a precipitation reaction.Features of a precipitation reaction include:

• The transformation of dissolved ions or substances into a solid state.
• The resulting solid is referred to as a precipitate—in this case, sulfur.

Such reactions are identifiable by a noticeable change, often the appearance of a solid as the reaction completes. Understanding precipitation reactions is essential in tasks such as predicting the outcomes of reactions in environmental chemistry, like volcanic activities, or managing waste in chemical processes.