Problem 11 - Chemistry for Allied Health

Question

Classify the following reactions as combination, decomposition, single replacement, double replacement, or combustion. For each, indicate if it is a redox reaction or not. a. \(\mathrm{Cd}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{CdSO}_{4}(a q)+\mathrm{H}_{2}(g)\) b. \(2 \mathrm{Fe}(s)+3 \mathrm{Cl}_{2}(g) \rightarrow 2 \mathrm{FeCl}_{3}(s)\) ?. \(\mathrm{C}_{7} \mathrm{H}_{8}(l)+9 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 7 \mathrm{CO}_{2}(\mathrm{~g})+4 \mathrm{H}_{2} \mathrm{O}(g)\) d. \(2 \mathrm{NH}_{4} \mathrm{NO}_{3}(s) \rightarrow 2 \mathrm{~N}_{2}(g)+\mathrm{O}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g)\) e. \(2 \mathrm{CoCl}_{3}(a q)+3 \mathrm{~Pb}\left(\mathrm{NO}_{3}\right)_{2}(a q) \rightarrow 2 \mathrm{Co}\left(\mathrm{NO}_{3}\right)_{3}(a q)+3 \mathrm{PbCl}_{2}(s)\)

Step-by-Step Solution

Answer

a: Single replacement, redox. b: Combination, redox. c: Combustion, redox. d: Decomposition, redox. e: Double replacement, not redox.

Step 1: Classify Reaction a

Examine the reaction \( \mathrm{Cd}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(aq) \rightarrow \mathrm{CdSO}_{4}(aq)+\mathrm{H}_{2}(g) \). This is a single replacement reaction because cadmium (Cd) replaces the hydrogen in \( \mathrm{H}_{2} \mathrm{SO}_{4} \). It is a redox reaction because Cd is oxidized and \( \mathrm{H}^{+} \) is reduced.

Step 2: Classify Reaction b

Examine the reaction \( 2 \mathrm{Fe}(s)+3 \mathrm{Cl}_{2}(g) \rightarrow 2 \mathrm{FeCl}_{3}(s) \). This is a combination reaction as iron (Fe) and chlorine gas (\( \mathrm{Cl}_{2} \)) combine to form iron(III) chloride (\( \mathrm{FeCl}_{3} \)). It is also a redox reaction, with Fe being oxidized and \( \mathrm{Cl}_{2} \) being reduced.

Step 3: Classify Reaction c

Examine the reaction \( \mathrm{C}_{7} \mathrm{H}_{8}(l)+9 \mathrm{O}_{2}(g) \rightarrow 7 \mathrm{CO}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g) \). This is a combustion reaction as it involves \( \mathrm{C}_{7} \mathrm{H}_{8} \) reacting with \( \mathrm{O}_{2} \) to produce \( \mathrm{CO}_{2} \) and \( \mathrm{H}_{2} \mathrm{O} \). It is a redox reaction, with carbon being oxidized and oxygen reduced.

Step 4: Classify Reaction d

Examine the reaction \( 2 \mathrm{NH}_{4} \mathrm{NO}_{3}(s) \rightarrow 2 \mathrm{~N}_{2}(g)+\mathrm{O}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g) \). This is a decomposition reaction as ammonium nitrate (\( \mathrm{NH}_{4} \mathrm{NO}_{3} \)) breaks down into nitrogen gas, oxygen gas, and water. It is a redox reaction since nitrogen is both being oxidized and reduced.

Step 5: Classify Reaction e

Examine the reaction \( 2 \mathrm{CoCl}_{3}(aq)+3 \mathrm{Pb}(\mathrm{NO}_{3})_{2}(aq) \rightarrow 2 \mathrm{Co}(\mathrm{NO}_{3})_{3}(aq)+3 \mathrm{PbCl}_{2}(s) \). This is a double replacement reaction where the ions exchange places between the reactants to form new compounds. It is not a redox reaction because no oxidation or reduction occurs.

Key Concepts

Reaction Classification

Chemical reactions can appear complex, but breaking them into categories helps make them easier to understand. Here are the main types of reaction classifications you might encounter:

• **Combination Reaction:** Two or more reactants combine to form a single product. It's like pieces of a puzzle coming together to make a complete picture.
• **Decomposition Reaction:** A single compound breaks down into two or more simpler substances. Think of it as taking apart a model to get the individual pieces.
• **Single Replacement Reaction:** One element in a compound is replaced by another element. Imagine swapping players on a basketball team lineup.
• **Double Replacement Reaction:** Two compounds swap elements to form two new compounds. This can be seen as two couples trading dance partners.
• **Combustion Reaction:** A substance combines with oxygen, releasing energy, often as heat and light, forming oxides such as carbon dioxide and water.

Classifying reactions helps in understanding their nature and the chemical changes occurring.

Redox Reactions

Redox (reduction-oxidation) reactions are like a see-saw of electron transfer. In these reactions:

• **Oxidation** involves the loss of electrons by a molecule, atom, or ion.
• **Reduction** involves the gain of electrons by a molecule, atom, or ion.

These two processes always occur simultaneously because as one substance loses electrons, another gains them. For example, consider the reaction of iron with chlorine to form iron(III) chloride (\(2 \text{Fe}(s) + 3 \text{Cl}_2(g) \rightarrow 2 \text{FeCl}_3(s)\)): iron is oxidized, losing electrons, while chlorine is reduced, gaining those electrons. Thus, analyzing whether a reaction is a redox reaction involves tracking the movement of electrons between the reacting species.

Single Replacement Reaction

In a single replacement reaction, one element replaces another in a compound. This type of reaction is also known as a single displacement or substitution reaction. The general form is:\[ A + BC \rightarrow AC + B \]Where element A replaces element B in compound BC, forming a new compound AC, and releasing element B. For example, in the reaction: \[ \text{Cd}(s) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{CdSO}_4(aq) + \text{H}_2(g) \]Cadmium (Cd) takes the place of hydrogen in sulfuric acid, creating cadmium sulfate and hydrogen gas. These reactions are important in processes like galvanization and extractive metallurgy.

Combination Reaction

Combination reactions involve two or more substances uniting to form a single new product. They can often be identified by having multiple reactants but only one product. The general formula is:\[ A + B \rightarrow AB \]A common example is the formation of rust: \[ 4 \text{Fe}(s) + 3 \text{O}_2(g) \rightarrow 2 \text{Fe}_2\text{O}_3(s) \]In our exercise, the combination reaction can be seen in the formation of iron(III) chloride:\[ 2 \text{Fe}(s) + 3 \text{Cl}_2(g) \rightarrow 2 \text{FeCl}_3(s) \]Such reactions are crucial because they often release energy, which is harnessed in various applications, from energy generation to the creation of industrial products.

Combustion Reaction

Combustion reactions involve a substance reacting with oxygen and releasing energy. Often producing heat and light, these reactions are the foundation for engines and heating systems. The basic form involves a hydrocarbon reacting with oxygen:\[ \text{C}_x\text{H}_y + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \]The example we examined involves toluene burning in oxygen:\[ \text{C}_7\text{H}_8(l) + 9 \text{O}_2(g) \rightarrow 7 \text{CO}_2(g) + 4 \text{H}_2\text{O}(g) \]In this process, carbon in toluene is oxidized, and the oxygen is reduced. Combustion reactions are not only essential for generating energy but also play a significant role in industrial processes that produce everyday goods and energy.