Question

Each of the following compounds produces \(\mathrm{O}_{2}(\mathrm{g})\) when strongly heated: (a) \(\mathrm{HgO}(\mathrm{s}) ;\) (b) \(\mathrm{KClO}_{4}(\mathrm{s})\) (c) \(\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{s}) ;\) (d) \(\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq}) .\) Write a plausible equation for the reaction that occurs in each instance.

Short answer

Reactions: (a) \(\mathrm{2HgO}(\mathrm{s}) \rightarrow \mathrm{2Hg}(\mathrm{l}) + \mathrm{O}_{2}(\mathrm{g}) ,\) (b) \(\mathrm{2KClO}_{4}(\mathrm{s}) \rightarrow \mathrm{2KCl}(\mathrm{s}) + \mathrm{7O}_{2}(\mathrm{g}) ,\) (c) \(\mathrm{2Hg}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{s}) \rightarrow \mathrm{2Hg}(\mathrm{l}) + \mathrm{4NO}_{2}(\mathrm{g}) + \mathrm{O}_{2}(\mathrm{g}) ,\) and (d) \(\mathrm{2H}_{2} \mathrm{O}_{2}(\mathrm{aq}) \rightarrow \mathrm{2H}_{2}\mathrm{O}(\mathrm{l}) + \mathrm{O}_{2}(\mathrm{g}).\)

Step-by-step solution

Reaction of HgO (Mercury Oxide)

When mercury oxide is heated strongly, it decomposes to yield mercury and oxygen. The balanced reaction is \(\mathrm{2HgO}(\mathrm{s}) \rightarrow \mathrm{2Hg}(\mathrm{l}) + \mathrm{O}_{2}(\mathrm{g}) .\)

Reaction of KClO4 (Potassium Perchlorate)

Potassium perchlorate is decomposed into potassium chloride and oxygen gas upon heating. This can be represented as \(\mathrm{2KClO}_{4}(\mathrm{s}) \rightarrow \mathrm{2KCl}(\mathrm{s}) + \mathrm{7O}_{2}(\mathrm{g}) . \)

Reaction of Hg(NO3)2 (Mercury Nitrate)

When heated, mercury nitrate undergoes thermal decomposition to yield mercury, nitrogen dioxide and oxygen. This is represented as \(\mathrm{2Hg}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{s}) \rightarrow \mathrm{2Hg}(\mathrm{l}) + \mathrm{4NO}_{2}(\mathrm{g}) + \mathrm{O}_{2}(\mathrm{g}) . \)

Reaction of H2O2 (Hydrogen Peroxide)

When heated, hydrogen peroxide decomposes to form water and oxygen, which can be represented as \(\mathrm{2H}_{2} \mathrm{O}_{2}(\mathrm{aq}) \rightarrow \mathrm{2H}_{2}\mathrm{O}(\mathrm{l}) + \mathrm{O}_{2}(\mathrm{g}) . \)

Key concepts

Thermal Decomposition

Thermal decomposition refers to the process by which a chemical compound breaks down into simpler substances when exposed to high temperatures. This kind of reaction is endothermic, meaning it absorbs heat from its surrounding environment. Heat supplies the energy needed to break the chemical bonds within the compound.

For example, the compound mercury(II) oxide ox{HgO} breaks into mercury ox{Hg} and oxygen gas ox{O_2} when heated. Similarly, hydrogen peroxide ox{H_2O_2} decomposes into water ox{H_2O} and oxygen gas when it undergoes thermal decomposition. These reactions often produce gaseous oxygen as one of the products, a characteristic feature of many thermal decomposition processes. Understanding thermal decomposition is key in various scientific fields, including chemistry and materials science.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They show the substances involved in the reaction and the process in a balanced manner. The substances you start with are called reactants, and the substances which are formed are called products.

Each chemical equation should be balanced, which means you have the same number of each type of atom on both sides of the equation. This is based on the law of conservation of mass. For example, the thermal decomposition of mercury(II) nitrate, ox{Hg(NO_3)_2}, produces mercury ox{Hg}, nitrogen dioxide ox{NO_2}, and oxygen gas ox{O_2}. The balanced equation for this reaction is: \[\mathrm{2Hg(NO_3)_2(s)} \rightarrow \mathrm{2Hg(l)} + \mathrm{4NO_2(g)} + \mathrm{O_2(g)}.\]

Writing accurate chemical equations is crucial in understanding the stoichiometry of reactions, allowing us to predict the quantities of reactants needed and the products formed.

Oxygen Gas Production

Oxygen gas production involves any reaction where oxygen (ox{O_2}) is one of the end products. This type of reaction is common in thermal decomposition processes. Oxygen is often released because it is a stable diatomic molecule that forms from certain compounds under heat.

For example, potassium perchlorate ox{KClO_4} when heated, decomposes into potassium chloride ox{KCl} and releases oxygen gas. The reaction is expressed as: \[\mathrm{2KClO_4(s)} \rightarrow \mathrm{2KCl(s)} + \mathrm{7O_2(g)}.\]

These reactions are not just important in laboratory settings but also have industrial applications. Oxygen gas production is crucial in fields such as metallurgy, where it is used in processes like smelting. Understanding how oxygen gas is produced helps explain many natural and industrial chemical processes.