Problem 95 - Introductory Chemistry Atoms First

Question

Classify each reaction as combination, decomposition, single-replacement, or double-replacement: (a) \(2 \mathrm{NaCl} \rightarrow 2 \mathrm{Na}+\mathrm{Cl}_{2}\) (b) \(\mathrm{Ba}_{3} \mathrm{~N}_{2} \rightarrow 3 \mathrm{Ba}+\mathrm{N}_{2}\) (c) \(\mathrm{Cl}_{2}+2 \mathrm{NaI} \rightarrow 2 \mathrm{NaCl}+\mathrm{I}_{2}\) (d) \(\mathrm{KNO}_{3}+\mathrm{AgBr} \rightarrow \mathrm{AgNO}_{3}+\mathrm{KBr}\)

Step-by-Step Solution

Answer

(a) Decomposition (b) Decomposition (c) Single-replacement (d) Double-replacement

Step 1: Definition of Combination Reaction

A combination reaction is a reaction in which two or more reactants combine to form a single product.

Step 2: Definition of Decomposition Reaction

A decomposition reaction is a reaction in which a single reactant breaks down into two or more simpler products.

Step 3: Definition of Single-Replacement Reaction

A single-replacement reaction is a reaction in which a more reactive element in a reactant compound is replaced by a less reactive element.

Step 4: Definition of Double-Replacement Reaction

A double-replacement reaction is a reaction in which the ions of two compounds exchange places, resulting in the formation of two new compounds. Now, let's analyze and classify each reaction:

Step 5: Reaction (a) Classification

Given: \(2 \mathrm{NaCl} \rightarrow 2 \mathrm{Na} + \mathrm{Cl}_{2}\) In this reaction, we have one reactant (\(NaCl\)), which breaks down into its constituent elements, sodium (\(Na\)) and chlorine (\(Cl_2\)), as the products. This is an example of a decomposition reaction.

Step 6: Reaction (b) Classification

Given: \(\mathrm{Ba}_{3} \mathrm{~N}_{2} \rightarrow 3 \mathrm{Ba} + \mathrm{N}_{2}\) In this reaction, we have one reactant (\(Ba_3N_2\)), which breaks down into its constituent elements, barium (\(Ba\)) and nitrogen (\(N_2\)), as the products. This is another example of a decomposition reaction.

Step 7: Reaction (c) Classification

Given: \(\mathrm{Cl}_{2} + 2 \mathrm{NaI} \rightarrow 2 \mathrm{NaCl} + \mathrm{I}_{2}\) In this reaction, we have two reactants (\(Cl_2\) and \(NaI\)). The more reactive element, chlorine (\(Cl_2\)), replaces the less reactive element, iodine (\(I\)), in the compound \(NaI\), resulting in the formation of \(2 NaCl\) and iodine (\(I_2\)). This is an example of a single-replacement reaction.

Step 8: Reaction (d) Classification

Given: \(\mathrm{KNO}_{3} + \mathrm{AgBr} \rightarrow \mathrm{AgNO}_{3} + \mathrm{KBr}\) In this reaction, we have two reactants (\(KNO_3\) and \(AgBr\)). The ions of the two compounds (\(K^+\) and \(NO_3^-\) in \(\mathrm{KNO}_{3}\), \(Ag^+\) and \(Br^-\) in \(\mathrm{AgBr}\)) exchange places, resulting in the formation of two new compounds (\(AgNO_3\) and \(KBr\)). This is an example of a double-replacement reaction.

Key Concepts

Combination Reaction

A combination reaction, also known as a synthesis reaction, is where two or more reactants come together to form a single product. Imagine putting together pieces of a puzzle to create one complete image; that's what happens during this type of reaction. It is like bringing different elements or compounds into a single, new unit.

• Reactants: Two or more elements or compounds
• Product: A single compound

Combination reactions are often exothermic, releasing energy in the form of heat. This process is commonly seen in the formation of compounds, such as water from hydrogen and oxygen:
\[ 2H_2 + O_2 ightarrow 2H_2O \].
This type of reaction is fundamental in various natural and industrial processes, including the manufacture of many everyday substances.

Decomposition Reaction

Decomposition reactions are the breakdown of a compound into two or more simpler substances. Think of it as taking apart a completed puzzle into its individual pieces. These reactions typically require energy input, often in the form of heat, light, or electricity, to break down the complex molecules.

• Reactant: A single compound
• Products: Two or more simpler compounds or elements

An example of a decomposition reaction is the breakdown of hydrogen peroxide into water and oxygen gas:
\[ 2H_2O_2 ightarrow 2H_2O + O_2 \].
Decomposition reactions are crucial in recycling and biological systems, where substances are broken down for reuse or removal.

Single-Replacement Reaction

In a single-replacement reaction, one element in a reactant compound is replaced by another more reactive element. Think of this as a switcheroo, where one element "kicks out" another from the compound. These reactions help in extracting metals from their ores and are commonly used in redox processes.

• Reactants: An element and a compound
• Products: A new element and a new compound

A classic example is when zinc replaces hydrogen in hydrochloric acid
\[ Zn + 2HCl ightarrow ZnCl_2 + H_2 \].
The reactivity series, which lists elements by their tendency to displace others, plays a key role in predicting and understanding these reactions.

Double-Replacement Reaction

Double-replacement reactions involve the exchange of ions between two compounds. It’s like a swap meet where partners exchange items, resulting in new combinations. These reactions commonly form a precipitate, a gas, or water, driving the reaction forward.

• Reactants: Two ionic compounds
• Products: Two new ionic compounds

An example involves the reaction of lead(II) nitrate with potassium iodide:
\[ Pb(NO_3)_2 + 2KI ightarrow 2KNO_3 + PbI_2 \].
In this reaction, the ions "swap partners" to form lead(II) iodide, which is an insoluble precipitate, and soluble potassium nitrate. These reactions are essential in various chemical processes, such as the production of common salts.