Question

Tick the correct option: burning of coal is a/an……………. change.
(A) Reversible
(B) Irreversible
(C) Natural
(D) Human made

Answer 1

Chemical reaction is defined as a process which involves conversion of one form of substance into another form. The substance formed at the end of reaction is called product. Chemical reaction completed with either chemical change or physical change in the reactant.

Complete Step By Step Answer:
Reversible chemical reaction is a reaction in which change of reactant to final product and change of final product to reactant occurs simultaneously. In reversible reaction, when the reaction proceeds, the amount of reactant reduces but we can recover the reactant from these types of reaction because they are feasible in forward as well as backward direction.
For example- formation of hydrogen iodide by hydrogen gas and iodine gas in a closed chamber.
${H_{2\left( g \right)}} + {I_{2\left( g \right)}} \rightleftharpoons 2H{I_{\left( g \right)}}$
Irreversible chemical reaction is a reaction in which change of reactant to final product and change of final product to reactant does not occur simultaneously. In an irreversible reaction, when the reaction proceeds, the amount of reactant reduces and ultimately exhausted from the product. we cannot recover the reactant from these types of reaction because they are not feasible in backward direction.
For example- burning of coal or other fuels in order to generate energy. As we know coal is a fossil and made up of hydrogen and carbon only so when we burn coal, the carbon content of coal is converted into carbon dioxide gas while hydrogen content of coal gets converted into water. Once the reaction is complete, we are not able to generate coal again from the released gases.
$coal \to C{O_2} + {H_2}O$
Natural reactions are chemical reactions which can proceed spontaneously without the need of any external triggering agent. Natural reactions occur in our day to day life like the process of conversion of carbon dioxide and water into glucose by plants via photosynthesis.
$6C{O_2} + 6{H_2}O \to {C_6}{H_{12}}{O_6} + 6{O_2}$
Chemical reactions which do not occur in nature spontaneously and require some external means to trigger the chemical reaction are known as man-made or human-made reactions. Reactions which include formation of polymers from their monomers are human-made reactions.
$n{C_2}{H_4} \to {\left( {{C_2}{H_4}} \right)_n}$
$\Rightarrow$ From the above discussion we conclude that burning of coal is an irreversible reaction.
Therefore, option $\left( B \right)$ is the correct option.

Note:
Reversible reactions are commonly known as bidirectional reactions and irreversible reactions are commonly known as unidirectional reactions. Ionization of strong electrolytes is also an example of irreversible reaction. Process of combustion, digestion, aerobic respiration in organisms are some other examples of natural reactions. Formation of pesticides, insecticides, organophosphorus compounds are also man-made reactions.