Problem 37 - Chemistry The Central Science

Question

Write balanced equations for each of the following reactions.(a) When mercury (II) oxide is heated, it decomposes to form \(\mathrm{O}_{2}\) and mercury metal. (b) When copper(II) nitrate is heated strongly, it decomposes to form copper(II) oxide, nitrogen dioxide, and oxygen. (c) Lead(II) sulfide, PbS(s) reacts with ozone to form PbSO \(_{4}(s)\) and \(\mathrm{O}_{2}(g) .\) (d) When heated in air, \(Z n S(s)\) is converted to ZnO. (e) Potassium peroxide reacts with \(\mathrm{CO}_{2}(g)\) to give potassium carboate and \(\mathrm{O}_{2} .(\mathbf{f})\) Oxygen is converted to ozone in the upper atmosphere.

Step-by-Step Solution

Answer

(a) \(2HgO \rightarrow O_2 + 2Hg\) (b) \(2Cu(NO_3)_2 \rightarrow 2CuO + 4NO_2 + O_2\) (c) \(PbS + 2O_3 \rightarrow PbSO_4 + O_2\) (d) \(ZnS + 3O_2 \rightarrow 2ZnO\) (e) \(2K_2O_2 + CO_2 \rightarrow K_2CO_3 + 2O_2\) (f) \(3O_2 \rightarrow 2O_3\)

Step 1: (a) Mercury(II) oxide decomposing to form O2 and mercury metal

Write the reaction: \[HgO \rightarrow O_2 + Hg\] Balance the equation: \[2HgO \rightarrow O_2 + 2Hg\]

Step 2: (b) Copper(II) nitrate decomposing to form copper(II) oxide, nitrogen dioxide, and oxygen

Write the reaction: \[Cu(NO_3)_2 \rightarrow CuO + NO_2 + O_2\] Balance the equation: \[2Cu(NO_3)_2 \rightarrow 2CuO + 4NO_2 + O_2\]

Step 3: (c) Lead(II) sulfide reacting with ozone to form PbSO4 and O2

Write the reaction: \[PbS + O_3 \rightarrow PbSO_4 + O_2\] Balance the equation: \[PbS + 2O_3 \rightarrow PbSO_4 + O_2\]

Step 4: (d) Zinc sulfide being converted to zinc oxide when heated in air

Write the reaction: \[ZnS + O_2 \rightarrow ZnO\] Balance the equation: \[ZnS + 3O_2 \rightarrow 2ZnO\]

Step 5: (e) Potassium peroxide reacting with CO2 to give potassium carbonate and O2

Write the reaction: \[K_2O_2 + CO_2 \rightarrow K_2CO_3 + O_2\] Balance the equation: \[2K_2O_2 + CO_2 \rightarrow K_2CO_3 + 2O_2\]

Step 6: (f) Oxygen being converted to ozone in the upper atmosphere

Write the reaction: \[O_2 \rightarrow O_3\] Balance the equation: \[3O_2 \rightarrow 2O_3\]

Key Concepts

Balancing Equations

Balancing chemical equations is a foundational skill in chemistry that ensures the same number of atoms for each element appear on both sides of a chemical reaction. This step is crucial because atoms are neither created nor destroyed in chemical reactions. Let's examine the process of balancing equations using a specific reaction, such as the decomposition of Mercury(II) oxide (HgO). Initially, the decomposition reaction is \[HgO \rightarrow O_2 + Hg\]This is unbalanced as there were two oxygen atoms on the right side and only one on the left. To balance it, you need two HgO molecules:\[2HgO \rightarrow O_2 + 2Hg\]Now, we see an equal count of each element on both sides:

• 2 Hg atoms
• 2 O atoms

Another example is the decomposition of Copper(II) nitrate. Start by writing:\[Cu(NO_3)_2 \rightarrow CuO + NO_2 + O_2\]To balance, adjust to \[2Cu(NO_3)_2 \rightarrow 2CuO + 4NO_2 + O_2\]Successfully balancing requires ensuring all elements have equal atoms on both reaction sides.

Decomposition Reactions

Decomposition reactions are a type of chemical reaction where a single compound breaks down into two or more simpler substances. These reactions often require energy input, like heat. For instance, the decomposition of Mercury(II) oxide involves heating, resulting in the formation of mercury metal and oxygen gas:\[2HgO \rightarrow 2Hg + O_2\]Similarly, heating Copper(II) nitrate initiates a decomposition process:\[2Cu(NO_3)_2 \rightarrow 2CuO + 4NO_2 + O_2\]Throughout decomposition reactions, you often witness:

• Release of gases: such as oxygen or nitrogen dioxide.
• Formation of simpler compounds: like metal oxides.
• Endothermic nature: they absorb energy.

Understanding decomposition can help in predicting reaction products and recognizing their application in various industrial and laboratory settings.

Synthesis of Ozone

Ozone synthesis entails converting molecular oxygen (\(O_2\)) into ozone (\(O_3\)), a process primarily occurring in the upper atmosphere. It involves several steps and is crucial for forming the earth's protective ozone layer. The direct equation for the synthesis is:\[3O_2 \rightarrow 2O_3\]This depicts how three oxygen molecules rearrange to form two ozone molecules. This balance ensures that the atom count for oxygen remains the same on both sides of the equation. However, in real-world applications, ultraviolet (UV) radiation plays a key role by breaking down \(O_2\) into individual oxygen atoms (\(O\)), which can then recombine to form ozone (\(O_3\)). In essence, ozone synthesis is a natural, continuous process significant for blocking harmful solar radiation from reaching the Earth's surface.

Reaction with Ozone

When discussing reactions with ozone, we often refer to it as the reactant actively doing chemistry with other substances. Ozone is a potent oxidizing agent, which means it can readily cause other compounds to lose electrons. Consider the reaction between Lead(II) sulfide (\(PbS\)) and ozone:\[PbS + 2O_3 \rightarrow PbSO_4 + O_2\]Here's what happens:

• Ozone oxidizes substances by adding oxygen to them, forming oxides such as \(PbSO_4\).
• The reaction produces oxygen gas (\(O_2\)) as a byproduct.

Because of its reactivity, ozone is used in various applications, from water purification to treating materials. However, its strong oxidative properties can pose challenges, requiring careful handling and control in industrial or laboratory environments.