Question

Combustion can be considered as

• A. oxidation
• B. reduction
• C. decomposition
• D. all of these

Answer 1

The correct option is A

oxidation

Explanation for the correct option:

A:

• A combustion reaction is a process in which reactants undergo reaction with the oxygen molecule $\left({\mathrm{O}}_2\right)$ to form the desired product along with the evolution of heat.
• In the case of hydrocarbons, carbon dioxide $\left({\mathrm{CO}}_2\right)$ and water $\left({\mathrm{H}}_2\mathrm{O}\right)$ are formed as products. Example:
• $\underset{\mathrm{Methane}}{{\mathrm{CH}}_4\left(\mathrm{g}\right)}+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$
• The reaction corresponding to the gain of oxygen (O) or loss of hydrogen (H) by a carbon (C) in methane $\left({\mathrm{CH}}_4\right)$ is called an oxidation reaction. Due to the addition of oxygen to the other reactant species, a combustion reaction can also be categorized as an oxidation reaction.

Explanation for incorrect options:

B:

• The reaction corresponding to the loss of Oxygen or gain of Hydrogen by a species is called a reduction reaction. Example:
• $\underset{\mathrm{Magnesium}\mathrm{oxide}}{\mathrm{MgO}\left(\mathrm{s}\right)}+\underset{\mathrm{Carbon}}{\mathrm{C}\left(\mathrm{s}\right)}\to \underset{\mathrm{Magnesium}}{\mathrm{Mg}\left(\mathrm{s}\right)}+\underset{\mathrm{Carbon}\mathrm{monoxide}}{\mathrm{CO}\left(\mathrm{g}\right)}$
• In this reaction, magnesium oxide $\left(\mathrm{MgO}\right)$ loses oxygen atom to form Magnesium, and therefore, it is getting reduced. Carbon gains Oxygen atom to form Carbon monoxide and hence, C is getting oxidized.

C:

• The reaction in which either two or more compounds are formed from a single reactant molecule is termed a decomposition reaction. Example:

$\underset{\mathrm{Limestone}\mathrm{or}\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}\stackrel{∆}{\to }\underset{\mathrm{Quick}\mathrm{lime}\mathrm{or}\mathrm{Calcium}\mathrm{oxide}}{\mathrm{CaO}}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2}$

Hence, the correct option is A. Combustion can be considered an oxidation reaction.