Difference Between Complete Combustion and Incomplete Combustion (with Table)

The main essence of a combustion reaction is that it involves O-oxygen and that it is an exothermic reaction. Combustion reactions release energy in the form of heat and light. Please note that it is necessary for a combustion reaction for oxygen (O2). However, the quantity of oxygen present in the reaction may vary depending on the other reactants and other environmental factors.

An example of a combustion reaction involving Propane and oxygen is as below:


Combustion reactions can be of two types depending on the amount of oxygen that is available for the reaction.

Complete Combustion vs Incomplete Combustion

The main difference between Complete Combustion and Incomplete Combustion is the amount of oxygen available for it. If the amount is sufficient or more, it is a Complete Combustion reaction and if it is less, it is an Incomplete Combustion reaction.

When there is a sufficient or an abundant amount of oxygen available during the process of combustion, then the reaction is known as a Complete Combustion reaction. Usually, this reaction occurs with a blue flame with no smoke.

When the amount of oxygen is insufficient for the process of combustion, then the reaction is known as an Incomplete Combustion reaction. This reaction is usually accompanied by a yellow sooty flame.

Comparison Table Between Complete Combustion and Incomplete Combustion

Parameters of Comparison

Complete Combustion

Incomplete Combustion


The combustion reaction which takes place in the presence of a sufficient or abundant amount of oxygen. Also known as Complete Combustion.

The combustion reaction that takes place in the presence of an insufficient amount of oxygen.





No smoke



Usually produces CO2 (Carbon Dioxide) as a primary product.

Usually produces CO (Carbon Monoxide) as a primary product.

Energy Production

Produces more energy as compared to Incomplete Combustion when combusting the same reactants.

Produces lesser energy when compared to Complete Combustion when combusting same reactants.

What is Complete Combustion?

Complete combustion is the combustion process where the amount of oxygen involved in the relationship is sufficient in amount or more than required. oxygen plays the role of an oxidizing agent in this case.

Usually, these reactions take place with hydrocarbons being on the reactant side as reducing agents. Hydrocarbons and oxygen react together to form water and carbon dioxide. The other products which we get from this reaction are energy in the form of heat and light.

Since the atmosphere has only 21% oxygen, hence it is a little difficult to achieve Complete Combustion easily. This is the reason, whenever we burn stuff like wood, paper, and similar other items which contain hydrocarbons in them, we see a yellow flame, which is a sign of Incomplete Combustion, rather than a Complete Combustion reaction.

A few examples of Complete Combustion reactions are given below:

Complete Combustion of methane:

CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)

Methane here is the reducing agent that reacts with oxygen, which is the oxidizing agent. This gives us carbon dioxide and Hydrogen as the final products. It is observed that Methane employs 2 molecules of oxygen. That is the minimum amount of oxygen needed by methane.

Complete Combustion of methanol:

2CH3OH(g) + 3O2(g) → 2CO2(g) + 4H2O(g)

Similar to the above example, methanol too here is the reducing agent and oxygen acts as the oxidizing agent. Methanol is a more complex hydrocarbon and hence requires more molecules of oxygen and produces more water and carbon dioxide.

Complete Combustion of a substance gives the highest amount of energy possible which can be extracted. This is because all of the substance is successfully combusted.

This type of combustion is also called ‘clean combustion’ as the products formed by this combustion does not pollute or harm the environment in any way, since it is just carbon dioxide and water.

A very common example that we see of clean combustion is the burning of LPG in our homes, as it usually produces a clear blue flame and no smoke.

What is Incomplete Combustion?

An Incomplete Combustion reaction is a reaction where the amount of oxygen present in the reaction is insufficient then the required amount of oxygen needed to carry out the reaction in a complete manner.

Like Complete Combustion reactions, the reactants play the same role, where oxygen is an oxidizing agent, and the hydrocarbons are reducing agents.

Incomplete Combustion of Propane-LPG

2 C3H8 + 9 O2 → 4 CO2 + 2 CO + 8 H2O + Heat

Some people might state the fact that there is carbon dioxide present on the product side, and hence this will be a Complete Combustion reaction. However, it is to be noted that for this reaction to be a Complete Combustion reaction, there should not be a single molecule of carbon monoxide.

A very common example of Incomplete Combustion is the burning of coal. This produces a lot of soot and smoke and hence causes a lot of environmental degradation. This is why the use of coal is being tried to be done in a limited amount to reduce pollution levels.

Main Differences Between Complete Combustion and Incomplete Combustion

  1. The main difference between Complete Combustion and Incomplete Combustion reactions is the amount of oxygen. If the amount is sufficient or more, it will be a complete reaction, and if it is less than sufficient, it will be an incomplete reaction.
  2. Complete Combustion reactions are usually characterized by a blue and smoke-less flame. Incomplete Combustion reactions are characterized by a sooty, smokey yellow flame.
  3. The products of Complete reaction primarily include carbon dioxide (CO2) and water (H2O). Incomplete reactions produce carbon monoxide (CO) and water (H2O).
  4. The products of a complete combustion reaction are environment friendly and do not cause pollution whereas the products of an Incomplete Combustion reaction are major pollutants in today’s world.
  5. A complete combustion reaction produces more energy than an Incomplete Combustion reaction with the same product. This is because a complete combustion reaction utilizes the whole product, whereas Incomplete combustion utilizes only a part of it.


Combustion Reactions are an essential part of our day to day lives and have a pivotal role in nature. Both the types of combustion reactions discussed above are important for us, although a complete combustion reaction might seem to be more preferable than Incomplete Combustion reactions, as they give us the maximum amount of energy possible without any environmental pollution.

The ability of a complete combustion reaction to not produce any environmentally toxic product, yet give huge amounts of energy has found its way into the automobile industry. The combustion reaction between hydrogen and water to produce water is the main principle behind hydrogen cars. Optimal utilization of fuels and proper combustion can go along way in saving our environment.


  1. https://pubs.acs.org/doi/abs/10.1021/acscatal.7b02414
  2. https://www.sciencedirect.com/science/article/abs/pii/S0883292701000610