Question

Write one equation each for decomposition reactions where energy is supplied in the form of heat, light, or electricity.

Answer 1

Hint: Think about what the word decompose may mean in the context of a chemical reaction. Decomposition is the action of breaking down complex substances into their constituent parts.

Complete step by step solution:
A decomposition reaction is a reaction that includes the breakdown of a larger molecule into two or three of its constituent parts. This breakdown is only possible if the bonds between the atoms in the molecule are broken. The breakage of these bonds will require an amount of energy since bonds absorb energy while breaking bonds and release energy when formation of bonds takes place. This energy can be obtained in any form like heat, light, or electricity. Some examples of these decomposition reactions are:
- Decomposition by heat:
$$CaC{O}_3\stackrel{heat}{\to }CaO+C{O}_2$$
In this reaction, 1 mole of calcium carbonate decomposes into one mole of calcium oxide and one mole of carbon dioxide. A decomposition reaction that requires heat is known as a thermal decomposition reaction.
- Decomposition by light:
$$2AgCl\stackrel{sunlight}{\to }2Ag+C{l}_2$$
In this reaction, 2 moles of silver chloride decompose into 2 moles of silver metal and 1 mole of chlorine gas in the presence of sunlight. Silver chloride has very weak bonds, so they can easily be broken by the energy received from sunlight. A decomposition reaction that requires light is known as a photochemical decomposition reaction.
- Decomposition by electricity:
$$2H_{2}O\stackrel{electricity}{\to }2H_2+O_2$$
In this reaction, 2 moles of water decompose to form 2 moles of hydrogen gas and 1 mole of oxygen gas when electricity is passed through it. A decomposition reaction that requires light is known as an electrochemical decomposition reaction. This type of reaction is usually used in the process of purification of metals and is also known as electrolysis.

Note: Another reaction where decomposition occurs is the formation of free radicals. This reaction can also be classified as a decomposition reaction since the halogen gas molecules are broken down into their constituent free radicals in the presence of ultraviolet light. It is a kind of photochemical decomposition reaction.