91Ó°ÊÓ

Classify each of the following reactions as a combination reaction, decomposition reaction, displacement reaction, or combustion reaction. a. When they are heated, ammonium dichromate crystals, \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\), decompose to give nitrogen, water vapor, and solid chromium(III) oxide, \(\mathrm{Cr}_{2} \mathrm{O}_{3}\). b. When aqueous ammonium nitrite, \(\mathrm{NH}_{4} \mathrm{NO}_{2}\), is heated, it gives nitrogen and water vapor. c. When gaseous ammonia, \(\mathrm{NH}_{3}\), reacts with hydrogen chloride gas, HCl, fine crystals of ammonium chloride, \(\mathrm{NH}_{4} \mathrm{Cl}\), are formed. d. Aluminum added to an aqueous solution of sulfuric acid, \(\mathrm{H}_{2} \mathrm{SO}_{4}\), forms a solution of aluminum sulfate, \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) Hydrogen gas is released.

Step by step solution

01

Identify the Reaction Type for a

The reaction involves ammonium dichromate \((\mathrm{NH}_{4})_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) decomposing into nitrogen \(\mathrm{N}_2\), water vapor \(\mathrm{H}_2\mathrm{O}\), and chromium(III) oxide \(\mathrm{Cr}_{2}\mathrm{O}_{3}\). Since a single compound breaks down into multiple products, this is a **decomposition reaction**.

02

Identify the Reaction Type for b

In this reaction, ammonium nitrite \(\mathrm{NH}_{4}\mathrm{NO}_{2}\) decomposes into nitrogen \(\mathrm{N}_2\) and water vapor \(\mathrm{H}_2\mathrm{O}\). Again, a single compound breaking down into simpler substances characterizes this as a **decomposition reaction**.

03

Identify the Reaction Type for c

The reaction between ammonia \(\mathrm{NH}_{3}\) and hydrogen chloride \(\mathrm{HCl}\) produces ammonium chloride \(\mathrm{NH}_{4}\mathrm{Cl}\). Here, two reactants combine to form a single product, which is a characteristic of a **combination reaction**.

04

Identify the Reaction Type for d

In this reaction, aluminum \(\mathrm{Al}\) displaces hydrogen in sulfuric acid \(\mathrm{H}_{2}\mathrm{SO}_{4}\), forming aluminum sulfate \(\mathrm{Al}_{2}(\mathrm{SO}_{4})_{3}\) and releasing hydrogen gas \(\mathrm{H}_2\). This is a **displacement reaction**, often referred to as a single-replacement reaction.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Decomposition Reaction

In a decomposition reaction, a single compound breaks down into two or more simpler substances. This type of reaction is like popping open a toy with many smaller toys inside. It's an essential concept because it helps in understanding how complex compounds can be broken down to simpler forms.

**Key Characteristics of Decomposition Reaction:**

• Involves a single reactant.
• Produces multiple products.
• Often requires an input of energy, like heat.

For example, when ammonium dichromate \((\mathrm{NH}_4)_2 \mathrm{Cr}_2 \mathrm{O}_7\) is heated, it decomposes into nitrogen gas \(\mathrm{N}_2\), water vapor \(\mathrm{H}_2\mathrm{O}\), and solid chromium(III) oxide \(\mathrm{Cr}_2 \mathrm{O}_3\). This reaction is a classic illustration showing how one substance transforms into multiple products upon the application of heat.

Combination Reaction

Combination reactions occur when two or more reactants unite to form a single product. Imagine putting two puzzle pieces together to complete a picture. This type of reaction is also known as a synthesis reaction, as it points to forming a more complex product.

**Key Characteristics of Combination Reaction:**

• Involves two or more reactants.
• Produces a single product.
• Can involve elements or compounds.

Consider the reaction between ammonia \(\mathrm{NH}_3\) and hydrogen chloride \(\mathrm{HCl}\) gas that forms fine crystals of ammonium chloride \(\mathrm{NH}_4\mathrm{Cl}\). Here, two gases combine chemically to produce a solid compound, exemplifying a combination reaction.

Displacement Reaction

In displacement reactions, one element replaces another element in a compound. Picture it like musical chairs, where one player pushes another out of the chair. This type of reaction is significant in understanding how elements can change partners within compounds.

**Types of Displacement Reactions:**

• Single Displacement: One element replaces another in a compound.
• Double Displacement: Two elements in different compounds swap places.

The reaction where aluminum \(\mathrm{Al}\) is added to sulfuric acid \(\mathrm{H}_2\mathrm{SO}_4\), forming aluminum sulfate \(\mathrm{Al}_2(\mathrm{SO}_4)_3\) and releasing hydrogen gas \(\mathrm{H}_2\), is an example of a single displacement reaction. Here, aluminum takes the place of hydrogen, illustrating the concept effectively.

Reaction Classification

Classifying reactions helps chemists predict the products formed and understand the changes occurring at the molecular level. Just like sorting books by genre, reaction classification aids in organizing and simplifying chemical equations.

**Main Classes of Chemical Reactions:**

• Combination reactions: Two or more substances combine to form one product.
• Decomposition reactions: A single compound breaks down into two or more products.
• Displacement reactions: An element in a compound is replaced by another element.
• Combustion reactions: A substance combines with oxygen, often producing heat and light.

In the original problem, recognizing the specific type of reaction aids in identifying what products will result and the nature of the reaction mechanics. Understanding these categories is foundational to mastering the vast subject of chemistry.