In very simple terms, the combustion reaction is the type of chemical reaction that takes place between a compound and an oxidant in order to produce a new product along with generation of heat. In addition, there are some combustion reactions where along with heat, light and flame is also produced. The combustion reaction is also referred to as “burning”. The usual reaction for a combustion is when any hydrocarbon reacts with oxygen in order to produce carbon dioxide and water. A more general overview of the combustion reaction is, when a combustible material reacts with oxidizer in order to produce oxidized product. The process of combustion, releases heat so, this is an exothermic reaction but, there are instances where the rate of reaction is very slow and in those cases the temperature change is not noticeable.

 In case of inorganic combustion reactions, the products like carbon dioxide, heat and water may not be produced but can be recognized by the reaction with oxygen. For all combustion reaction it do not always result in fire but, if the reaction produces fire then flame is a characteristic for the reaction. In order to initiate a combustion, the activation energy must be overcome. The initialization of a combustion is often done by a burning match stick or any other source of flame. When the combustion has started, after that enough heat may be produced in order to sustain the reaction till oxygen or fuel is available to the reaction. Combustion reaction is a type of redox reaction. If the reactants are not O₂ or F₂ in a combustion reaction then the reactants are known as fuel.  

The general from for a combustion reaction:

hydrocarbon + oxygen → carbon dioxide + water

Few examples of combustion reaction:

• Combustion reaction of methane

CH₄ (g) + 2 O₂ (g) → CO₂ (g) + 2 H₂O (g)

• The burning of naphthalene

C₁₀H₈ + 12 O₂ → 10 CO₂ + 4 H₂O

• Ethane reacting with oxygen

2 C₂H₆ + 7 O₂ → 4 CO₂ + 6 H₂O

• The combustion of butane that is usually found in lighters

2 C₄H₁₀ (g) + 13 O₂ (g) → 8 CO₂ (g) +10 H₂O (g)

• Combustion of methanol or wood alcohol

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

• Reaction of propane that are used in gas grills as well as fireplaces

2 C₃H₈ (g) + 7 O₂ (g) → 6 CO₂ (g) + 8 H₂O (g)

• Burning of sugar

C₆H₁₂O₆ (s) + 12 O₂ (g) → 6 CO₂ (g) + 6 H₂O (g)

There can be two types of combustion. One can be complete combustion and the other can be incomplete combustion. Like any other reaction, a combustion reaction is not always totally efficient. In combustion reaction, the reactants can also be limited like any other process.

Complete combustion

The complete combustion is also known as “clean combustion”. In this type of combustion, a hydrocarbon is oxidized in order to produce carbon dioxide and water. One very practical example of complete combustion is the burning of candle wax. The heat generated from the wick of the candle, vaporizes the wax, which is a hydrocarbon. The hydrocarbon reacts with the air to produce carbon dioxide and water. In an ideal case, all the wax is burn and nothing is left after that and, the water vapour and carbon dioxide that is being produced is dissipated into the air.

Incomplete combustion

Another name for incomplete combustion is “dirty combustion”. The oxidation of hydrocarbon that yields carbon monoxide or carbon (soot) plus carbon dioxide. A very good example of incomplete combustion is burning of coal. A lot of soot and carbon monoxide is released during this reaction. A lot of fossil fuels burn incompletely, that releases waste products.

Balancing combustion reactions

Balancing any chemical reaction is important to complete the reaction. Balancing combustion reactions are easier. To balance a combustion reaction, the order of balancing the elements should be followed: carbon, hydrogen after that oxygen.

For an example take pentene (C₅H₁₂):

C₅H₁₂ + O₂ à  CO₂ + H₂O

Step 1 is to balance the carbon-

C₅H₁₂ + O₂ à 5 CO₂ + H₂O

Step 2 is to balance the hydrogen-

C₅H₁₂ + O₂ à 5 CO₂ + 6 H₂O

After that in step 3 the oxygen is balanced-

C₅H₁₂ + 8 O₂ à 5 CO₂ + 6 H₂O

Another example can be hexane (C₆H₁₄):

C₆H₁₄ + O₂ à   CO₂ + H₂O

Step 1:

C₆H₁₄ + O₂ à 6 CO₂ + H₂O

Step 2:

C₆H₁₄ + O₂ à 6 CO₂ + 7 H₂O 

Step 3: In this step it is noticed that there are 7+12=19 are there in the right side so we will need 19/2 of the O₂

C₆H₁₄ + 19/2 O₂ à 6 CO₂ + 7 H₂O

Step 4: Get rid of the fraction:

2 C₆H₁₄ + 19 O₂ à 12 CO₂ + 14 H₂O