Oxidation vs Combustion
Oxidation reduction reactions are a basic type of chemical reactions that we commonly come across in life.
Originally oxidation reactions were identified as the reactions in which oxygen gas participates. There, oxygen combines with another molecule to produce an oxide. In this reaction, oxygen undergoes reduction and the other substance undergoes oxidation. Therefore, basically, oxidation reaction is adding oxygen to another substance. For example, in the following reaction, hydrogen undergoes oxidation and, therefore, oxygen atom has added to hydrogen forming water.
2H2 + O2 -> 2H2O
Another way to describe oxidation is as loss of hydrogen. There are some occasions where it is hard to describe oxidation as adding oxygen. For example, in the following reaction, oxygen has added to both carbon and hydrogen, but only carbon has undergone oxidation. In this instance, oxidation can be described by saying it is the loss of hydrogen. As hydrogens have removed from methane when producing carbon dioxide, carbon there has been oxidized.
CH4 + 2O2 -> CO2 + 2H2O
Another alternative approach to describe oxidation is as losing of electrons. This approach can be used to explain chemical reactions, where we can’t see an oxide formation or hydrogen losing. So, even when there is no oxygen, we can explain oxidation using this approach. For example in the following reaction, magnesium has converted to magnesium ions. Since, magnesium has lost two electrons it has undergone oxidation and chlorine gas is the oxidizing agent.
Mg + Cl2 -> Mg2+ + 2Cl–
Oxidation state helps to identify the atoms that have undergone oxidation. According to the IUPAC definition, oxidation state is “a measure of the degree of oxidation of an atom in a substance. It is defined as the charge an atom might be imagined to have.” Oxidation state is an integer value, and it can be either positive, negative or zero. Oxidation state of an atom is subjected to change upon chemical reaction. If the oxidation state is increasing, then the atom is said to be oxidized. As in the above reaction, magnesium has zero oxidation state and magnesium ion has +2 oxidation state. Since the oxidation number has increased, magnesium has oxidized.
Combustion or heating is a reaction where heat is produced by an exothermic reaction. For the reaction to take place, a fuel and an oxidant should be there. Substances undergoing the combustion are known as fuels. These can be hydrocarbons like petrol, diesel, methane, or hydrogen gas, etc. Usually the oxidizing agent is oxygen, but there can be other oxidants like fluorine too. In the reaction, the fuel is oxidized by the oxidant. Therefore, this is an oxidation reaction. When hydrocarbon fuels are used, the products after a complete burning are usually carbon dioxide and water. However, if the burning didn’t happen completely, carbon monoxide and other particles can be released into the atmosphere, and that can cause a lot of pollution.
What is the difference between Oxidation and Combustion?
• Combustion is an oxidation reaction.
• For combustion, the usual oxidant is oxygen but, for an oxidation reaction to take place, oxygen is not essential.
• In combustion, the products are primarily water and carbon dioxide but, in oxidation, product can vary depending on the starting material. However, always they will have a higher oxidation state than the reactants.
• In combustion reactions, heat and light is produced, and work can be done from the energy. But for oxidation reactions, this is not always true.