Problem 14 - Chemistry: Atoms First

Question

Indicate what type, or types, of reaction each of the following represents: (a) \(\mathrm{H}_{2} \mathrm{O}(g)+\mathrm{C}(s) \longrightarrow \mathrm{CO}(g)+\mathrm{H}_{2}(g)\) (b) \(2 \mathrm{KClO}_{3}(s) \longrightarrow 2 \mathrm{KCl}(s)+3 \mathrm{O}_{2}(g)\) (c) \(\mathrm{Al}(\mathrm{OH})_{3}(a q)+3 \mathrm{HCl}(a q) \longrightarrow \mathrm{AlCl}_{3}(a q)+3 \mathrm{H}_{2} \mathrm{O}(l)\) (d) \(\operatorname{Pb}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{PbSO}_{4}(s)+2 \mathrm{HNO}_{3}(a q)\)

Step-by-Step Solution

Answer

(a) Redox reaction, (b) Decomposition reaction, (c) Acid-base neutralization, (d) Precipitation reaction (double displacement).

Step 1: Identify Reaction Type for (a)

Inspect the reactants and products in (a) to determine the reaction type. Here, a compound and an element react to form two new compounds, which characterizes a redox reaction. The carbon is being oxidized, and the water is being reduced.

Step 2: Identify Reaction Type for (b)

Examine the reactants and products in (b) to classify the reaction. This reaction involves the decomposition of potassium chlorate (KClO3) into potassium chloride (KCl) and oxygen gas (O2). Decomposition reactions involve a single compound breaking down into two or more simpler substances.

Step 3: Identify Reaction Type for (c)

Evaluate the reactants and products in (c) to ascertain the reaction type. Since an acid (HCl) reacts with a base (Al(OH)3) to produce a salt (AlCl3) and water (H2O), this reaction is an acid-base neutralization.

Step 4: Identify Reaction Type for (d)

Look at the reactants and products in (d) for reaction classification. Two aqueous compounds are reacting to form one solid product (PbSO4) in a double displacement reaction, also known as a precipitation reaction, since a precipitate is formed.

Key Concepts

Redox Reaction

Redox reactions, or oxidation-reduction reactions, are a fundamental type of chemical reaction where the oxidation state of atoms changes. Oxidation is the process of losing electrons, and reduction is the gain of electrons. In a redox reaction, one substance is oxidized while another is reduced.

To get a clearer picture, let's consider the given example (a) \(\mathrm{H}_{2} \mathrm{O}(g) + \mathrm{C}(s) \longrightarrow \mathrm{CO}(g) + \mathrm{H}_{2}(g)\). This reaction involves the transfer of electrons between chemical species. The carbon \(C\) is oxidized as it gains oxygen to form carbon monoxide \(CO\), while water \(H_2O\) is reduced to hydrogen gas \(H_2\).

Recognizing redox reactions is critical for students because these reactions are prevalent in both laboratory chemistry and in everyday processes such as combustion, respiration, and corrosion.

Decomposition Reaction

Decomposition reactions entail a single compound breaking apart into two or more simpler substances. These reactions often require an input of energy in the form of heat, light, or electricity.

The example (b) \(2 \mathrm{KClO}_{3}(s) \longrightarrow 2 \mathrm{KCl}(s) + 3 \mathrm{O}_{2}(g)\) illustrates a classical decomposition reaction. Here, potassium chlorate \(KClO_3\) decomposes into potassium chloride \(KCl\) and oxygen gas \(O_2\) when heated.

Decomposition reactions are important to understand for processes like the breakdown of organic matter, the digestion of food, and the production of metals from ores.

Acid-Base Neutralization

An acid-base neutralization is a type of chemical reaction where an acid and a base react to form water and a salt. This process is driven by the combination of H+ ions from the acid and OH- ions from the base to produce water.

The reaction shown in (c) \(\mathrm{Al}(\mathrm{OH})_{3}(aq) + 3 \mathrm{HCl}(aq) \longrightarrow \mathrm{AlCl}_{3}(aq) + 3 \mathrm{H}_{2} \mathrm{O}(l)\) is a perfect example. The hydrochloric acid \(HCl\) and aluminum hydroxide \(Al(OH)_3\) react to form aluminum chloride \(AlCl_3\), which is the salt, and water \(H_2O\).

Understanding neutralization is essential because it's widely used in various applications, including the treatment of acid reflux, the neutralization of soil acidity in agriculture, and in wastewater treatment.

Precipitation Reaction

Precipitation reactions occur when two aqueous solutions react to form an insoluble solid, known as a precipitate. These reactions are a subset of double displacement reactions and are important for identifying the presence of certain ions in a solution.

In the provided example (d) \(\operatorname{Pb}(\mathrm{NO}_{3})_{2}(aq) + \mathrm{H}_{2} \mathrm{SO}_{4}(aq) \longrightarrow \mathrm{PbSO}_{4}(s) + 2 \mathrm{HNO}_{3}(aq)\), lead nitrate and sulfuric acid react to form lead sulfate, which precipitates from the solution, and nitric acid.

Recognizing precipitation reactions helps in understanding processes like the purification of water, the formation of geological formations such as stalactites and stalagmites, and in medical diagnostics for the detection of certain ions in bodily fluids.