Problem 47 - Chemistry

Question

Write a balanced equation for each of the following processes: (a) On heating, ammonium nitrate produces nitrous oxide. (b) On heating, potassium nitrate produces potassium nitrite and oxygen gas. (c) On heating, lead nitrate produces lead(II) oxide, nitrogen dioxide \(\left(\mathrm{NO}_{2}\right),\) and oxygen gas.

Step-by-Step Solution

Answer

The balanced equations for the given processes are (a) \(NH_{4}NO_{3} \rightarrow N_{2}O + 2H_{2}O\), (b) \(2KNO_{3} \rightarrow 2KNO_{2} + O_{2}\), and (c) \(2Pb(NO_{3})_{2} \rightarrow 2PbO + 4NO_{2} + O_{2}\).

Step 1: Identify the reactants and products for reaction (a)

The reactant of this process is ammonium nitrate (NH4NO3) and the product is nitrous oxide (N2O). Writing out the unbalanced chemical equation for reaction (a): \(NH_{4}NO_{3} \rightarrow N_{2}O\).

Step 2: Balance the chemical equation for reaction (a)

To balance the chemical equation, balance the number of atoms for each element on both sides of the equation. In this case, adding water (H2O) as a product and keeping a count of two molecules of nitrous oxide leads to a balanced equation. Hence, the balanced equation for reaction (a) is: \(NH_{4}NO_{3} \rightarrow N_{2}O + 2H_{2}O\).

Step 3: Identify the reactants and products for reaction (b)

The reactant of this process is potassium nitrate (KNO3) and the products are potassium nitrite (KNO2) and oxygen gas (O2). Writing out the unbalanced chemical equation for reaction (b): \(KNO_{3} \rightarrow KNO_{2} + O_{2}\).

Step 4: Balance the chemical equation for reaction (b)

Balancing the chemical equation means the number of atoms for each element on both sides of the equation should be equal. Therefore, the balanced equation for reaction (b) is simply: \(2KNO_{3} \rightarrow 2KNO_{2} + O_{2}\).

Step 5: Identify the reactants and products for reaction (c)

For process (c), the reactant is lead nitrate (Pb(NO3)2) and the products are lead(II) oxide (PbO), nitrogen dioxide (NO2) and oxygen gas (O2). Write out the unbalanced chemical equation: \(Pb(NO_{3})_{2} \rightarrow PbO + NO_{2} + O_{2}\).

Step 6: Balance the chemical equation for reaction (c)

Balancing this complex chemical equation involves ensuring the same number of atoms for each element are present on both sides of the equation. Therefore, the balanced equation for reaction (c) is: \(2Pb(NO_{3})_{2} \rightarrow 2PbO + 4NO_{2} + O_{2}\).

Key Concepts

Ammonium Nitrate Decomposition

Ammonium nitrate decomposes when heated, producing different gases. This process is represented by a balanced chemical equation. During decomposition, ammonium nitrate (\(NH_4NO_3\)) breaks down to form nitrous oxide (\(N_2O\)) and water (\(H_2O\)). The equation representing this transformation is:

\(NH_4NO_3 \rightarrow N_2O + 2H_2O\)

This balanced equation reflects the law of conservation of mass, meaning the total number of each type of atom remains constant before and after the reaction.
Balancing equations, in this case, requires ensuring that nitrogen, hydrogen, and oxygen atoms are equal on both sides. For instance, after identifying that nitrogen atoms are present in both nitrous oxide and ammonium nitrate, the presence of any additional hydrogen atoms is then balanced with water molecules.

Potassium Nitrate Reaction

The decomposition of potassium nitrate when heated results in the formation of potassium nitrite and oxygen. In the unbalanced form, the reaction looks like this:

\(KNO_3 \rightarrow KNO_2 + O_2\)

To ensure this reaction obeys the law of conservation of mass, it needs to be balanced. The balanced form is:

\(2KNO_3 \rightarrow 2KNO_2 + O_2\)

The coefficients are used to balance the number of atoms of potassium, nitrogen, and oxygen on both sides of the equation. Two potassium nitrate molecules decompose to form two potassium nitrite molecules and one molecule of diatomic oxygen.This balancing ensures that every reactant atom is accounted for in the products after the reaction is complete, achieving a stable and correct representation of the chemical process.

Lead Nitrate Decomposition

When lead nitrate is heated, it decomposes into lead(II) oxide, nitrogen dioxide, and oxygen gas. This reaction can be a bit more complex due to the involvement of three different products. The unbalanced equation initially is:

\(Pb(NO_3)_2 \rightarrow PbO + NO_2 + O_2\)

By balancing this equation, we account for all atoms, achieving:

\(2Pb(NO_3)_2 \rightarrow 2PbO + 4NO_2 + O_2\)

In this balanced reaction, two lead nitrate molecules result in two lead(II) oxide molecules, four nitrogen dioxide molecules, and one diatomic oxygen molecule. The existence of multiple products makes such reactions interesting and emphasizes the necessity for balancing equations to respect the conservation principles in chemistry. Each element's quantity is meticulously managed on both the reactant and product sides, illustrating a perfect chemical transformation.