Question

a. Why is the following reaction called a decomposition reaction? $$ 2 \mathrm{Al}_{2} \mathrm{O}_{3}(s) \stackrel{\Delta}{\longrightarrow} 4 \mathrm{Al}(s)+3 \mathrm{O}_{2}(g) $$ b. Why is the following reaction called a single replacement reaction? $$ \mathrm{Br}_{2}(\mathrm{~g})+\mathrm{BaI}_{2}(s) \longrightarrow \mathrm{BaBr}_{2}(s)+\mathrm{I}_{2}(g) $$

Short answer

The first reaction is a decomposition reaction because \( \mathrm{Al}_{2} \mathrm{O}_{3} \) breaks down into \( \mathrm{Al} \) and \( \mathrm{O}_{2} \). The second reaction is a single replacement reaction because \( \mathrm{Br}_{2} \) replaces iodine in \( \mathrm{BaI}_{2} \).

Step-by-step solution

- Understand the Decomposition Reaction

A decomposition reaction involves a single compound breaking down into two or more simpler substances. Identify the reactant and the products in the given reaction: \[ 2 \mathrm{Al}_{2} \mathrm{O}_{3}(s) \stackrel{\Delta}{\longrightarrow} 4 \mathrm{Al}(s) + 3 \mathrm{O}_{2}(g) \]. Here, the reactant is \( 2 \mathrm{Al}_{2} \mathrm{O}_{3} \) and it breaks down into \( 4 \mathrm{Al} \) and \( 3 \mathrm{O}_{2} \).

- Identify Characteristics of Decomposition Reaction

Verify that the given equation has one reactant and multiple products. The equation \( 2 \mathrm{Al}_{2} \mathrm{O}_{3}(s) \stackrel{\Delta}{\longrightarrow} 4 \mathrm{Al}(s) + 3 \mathrm{O}_{2}(g) \) features \( \mathrm{Al}_{2} \mathrm{O}_{3} \) breaking down into \( \mathrm{Al} \) and \( \mathrm{O}_{2} \). This confirms it is a decomposition reaction.

- Explain the Concept of Decomposition

In decomposition reactions, compounds decompose or split into more basic elements or components under energy input (like heat, light, or electricity). Here, \( \mathrm{Al}_{2} \mathrm{O}_{3} \) breaks into \( \mathrm{Al} \) and \( \mathrm{O}_{2} \), which adheres to the definition.

- Understand the Single Replacement Reaction

A single replacement reaction involves an element replacing another in a compound. Consider the equation \( \mathrm{Br}_{2}(\mathrm{~g}) + \mathrm{BaI}_{2}(s) \longrightarrow \mathrm{BaBr}_{2}(s) + \mathrm{I}_{2}(g) \). Here, \( \mathrm{Br}_{2} \) replaces \( \mathrm{I} \) in \( \mathrm{BaI}_{2} \).

- Identify Characteristics of Single Replacement Reaction

Check that one element replaces another in a compound. In this case, \( \mathrm{Br}_{2} \) replaces iodine in \( \mathrm{BaI}_{2} \), forming \( \mathrm{BaBr}_{2} \) and \( \mathrm{I}_{2} \). This replacement indicates a single replacement reaction.

- Explain the Concept of Single Replacement

Single replacement reactions occur when one element displaces another in a compound, forming a new element and a new compound. Here, bromine replaces iodine in \( \mathrm{BaI}_{2} \) to form \( \mathrm{BaBr}_{2} \) and releases iodine. This agrees with the concept of single replacement.

Key concepts

Decomposition Reaction

A decomposition reaction occurs when a single compound breaks down into two or more simpler substances. For example, consider the reaction:
\ 2 Al_{2}O_{3} \rightarrow 4 Al + 3 O_{2}
Here, a single compound, \( Al_{2}O_{3} \), decomposes into aluminum (\( Al \)) and oxygen (\( O_{2} \)). This type of reaction usually requires energy input such as heat, light, or electricity.

In general, decomposition reactions can be identified by:

• One reactant
• Multiple products

These reactions are crucial in various industrial processes, such as extracting metals from their ores.

Single Replacement Reaction

A single replacement reaction involves an element replacing another element within a compound. For instance, consider:
\ Br_{2} + BaI_{2} \rightarrow BaBr_{2} + I_{2}
Here, bromine (\(Br_{2}\)) replaces iodine (\(I\)) in \(BaI_{2}\), forming \(BaBr_{2}\) and \(I_{2}\).

Key characteristics of single replacement reactions include:

• One element and one compound as reactants
• Formation of a new element and a new compound

These reactions often occur in aqueous solutions and can be influenced by the reactivity of the involved elements.

Reaction Types

Understanding different types of chemical reactions is fundamental to grasping chemistry concepts. Important reaction types include:

• Decomposition Reaction: A single compound breaks into two or more simpler substances.
• Single Replacement Reaction: An element replaces another in a compound.
• Double Replacement Reaction: Exchange of elements between two reacting compounds.
• Synthesis Reaction: Combining two or more simple substances to form a more complex compound.
• Combustion Reaction: A substance combines with oxygen, releasing heat and light.

Identifying these reaction types helps in predicting the products formed and understanding the energy changes involved.

Chemical Equations

Chemical equations represent a chemical reaction using symbols and formulas. They show the reactants converting into products. For instance:
\ 2 Al_{2}O_{3} \rightarrow 4 Al + 3 O_{2}
Here,

• Reactants: 2 units of \( Al_{2}O_{3} \)
• Products: 4 units of \( Al \) and 3 units of \( O_{2} \)

Chemical equations must be balanced, meaning the number of atoms for each element is the same on both sides. This conservation of mass reflects the law of conservation of matter in chemical reactions.

Element Displacement

Element displacement occurs in single replacement reactions, where one element displaces another within a compound. For example:
\ Zn + CuSO_{4} \rightarrow ZnSO_{4} + Cu
Here, zinc (\(Zn\)) displaces copper (\(Cu\)) from copper sulfate (\(CuSO_{4} \)).

The activity series of metals can predict the feasibility of displacement reactions. More reactive metals will displace less reactive metals from their compounds. This concept is crucial in understanding reactivity trends and the extraction of metals in metallurgy.