Problem 24 - Chemistry: Principles and Reactions

Question

Write a balanced equation for the reaction of hydrogen sulfide with (a) \(\mathrm{Cd}^{2+}\) (b) \(\mathrm{OH}^{-}\) (c) \(\mathrm{O}_{2}(g)\)

Step-by-Step Solution

Answer

Question: Write the balanced chemical equations for the reaction of hydrogen sulfide (H2S) with the following reactants: a) Cd2+, b) OH-, and c) O2(g). Answer: (a) H2S(aq) + Cd2+(aq) → CdS(s) + 2H+(aq) (b) H2S(aq) + 2 OH-(aq) → S2-(aq) + 2 H2O(l) (c) 2 H2S(g) + O2(g) → 2 H2O(l) + 2 S(s)

Step 1: Reaction of hydrogen sulfide with Cd2+

First, let's write the reactants and expected result for the reaction of hydrogen sulfide (H2S) with \(\mathrm{Cd}^{2+}(aq)\). The metal ion, \(\mathrm{Cd}^{2+}\), will react with hydrogen sulfide to form a new compound: $$\mathrm{H}_{2}\mathrm{S}(aq) + \mathrm{Cd}^{2+}(aq) \longrightarrow \mathrm{CdS}(s) + 2\mathrm{H}^{+}(aq)$$ Now, we need to balance the equation. In this case, there are 2 hydrogen atoms and 1 sulfur atom on both sides of the equation, and therefore, the equation is already balanced.

Step 2: Reaction of hydrogen sulfide with OH-

Next, let's write the reactants and expected results for the reaction of hydrogen sulfide (H2S) with \(\mathrm{OH}^{-}(aq)\). The hydroxide ion will react with hydrogen sulfide to form a new compound: $$\mathrm{H}_{2}\mathrm{S}(aq) + 2 \mathrm{OH}^{-}(aq) \longrightarrow \mathrm{S}^{2-}(aq) + 2\mathrm{H}_{2}\mathrm{O}(l)$$ Now, we need to balance the equation. In this case, we already have the correct number of atoms for each element, so the equation is balanced.

Step 3: Reaction of hydrogen sulfide with O2(g)

Lastly, let's write the reactants and expected results for the reaction of hydrogen sulfide (H2S) with oxygen gas, \(\mathrm{O}_{2}(g)\). The oxygen gas will react with hydrogen sulfide to form new compounds: $$2\mathrm{H}_{2}\mathrm{S}(g) + \mathrm{O}_{2}(g) \longrightarrow 2\mathrm{H}_{2}\mathrm{O}(l) + 2\mathrm{S}(s)$$ Now, we need to balance the equation. In this case, we already have the correct number of atoms for each element, so the equation is balanced. To summarize, the balanced equations for the reactions of hydrogen sulfide are: (a) \(\mathrm{H}_{2}\mathrm{S}(aq) + \mathrm{Cd}^{2+}(aq) \longrightarrow \mathrm{CdS}(s) + 2\mathrm{H}^{+}(aq)\) (b) \(\mathrm{H}_{2}\mathrm{S}(aq) + 2 \mathrm{OH}^{-}(aq) \longrightarrow \mathrm{S}^{2-}(aq) + 2\mathrm{H}_{2}\mathrm{O}(l)\) (c) \(2\mathrm{H}_{2}\mathrm{S}(g) + \mathrm{O}_{2}(g) \longrightarrow 2\mathrm{H}_{2}\mathrm{O}(l) + 2\mathrm{S}(s)\)

Key Concepts

Chemical Reactions

Chemical reactions are processes in which substances, known as reactants, transform into new substances called products. This transformation occurs through the breaking and forming of chemical bonds. These reactions involve changes on a molecular level and are governed by the laws of conservation of mass and energy.

The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. This means the total mass of the reactants must equal the total mass of the products. For a chemical equation to accurately represent this law, it needs to be balanced, with an equal number of atoms for each element on both sides of the equation.

In the example of the reaction of hydrogen sulfide with different substances, we see how the reactants hydrogen sulfide (H₂S) and another substance, undergo a chemical change to form new products. The balancing of these equations ensures that the number of atoms for each element is the same on both sides, reflecting the conservation of mass.

Stoichiometry

Stoichiometry is the study of the quantitative relationships between the amounts of reactants used and products formed in a chemical reaction. It's a central concept in chemistry that allows us to predict amounts of substances consumed and produced in reactions.

In stoichiometry, the coefficients in a balanced chemical equation tell us the ratio of moles of each substance involved. For example, the balanced equation for the reaction of hydrogen sulfide with cadmium ion (Cd²⁺) shows that one mole of H₂S reacts with one mole of Cd²⁺ to produce one mole of cadmium sulfide (CdS) and two moles of hydrogen ion (H⁺). Stoichiometry is used not only to balance chemical equations but also in practical applications such as determining the amount of reactants needed to produce a desired amount of product, and in calculating yields of chemical processes.

Reaction of Hydrogen Sulfide

Hydrogen sulfide (H₂S) is a toxic, flammable gas that smells like rotten eggs. It's commonly found in the natural environment, produced by the breakdown of organic matter and by certain industrial processes. In chemical reactions, H₂S can act as a reducing agent, meaning it donates electrons to other substances.

The reaction of hydrogen sulfide with different substances demonstrates various chemical behavior of H₂S. For instance, when H₂S reacts with cadmium ion, a metal sulfide is formed. When it reacts with hydroxide ions (OH^-), sulfide ion (S^2-) and water are the products. In the presence of oxygen (O₂), H₂S is oxidized, producing water and elemental sulfur. Understanding the reactivity of hydrogen sulfide is important in fields such as environmental science and industrial chemistry for controlling its release and handling it safely in chemical processes.