Combustion Reaction – Definition, Formula, Examples

Combustion Reaction

Combustion reaction refers to an exothermic chemical reaction that has high-temperature. It happens between a fuel (the reductant) and an oxidant, usually atmospheric oxygen that produces oxidized, often gaseous products, resulting in a mixture of smoke.

Combustion reaction in a fire produces a flame, and the heat emitting can thus make combustion self-sustaining. A combustion reaction is often a complicated sequence of elementary radical reactions.

 

Meaning of Combustion Reaction

Wood and coal, etc all these solid-fuel first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them.

The combustion reaction of an organic fuel in air is always exothermic because the double bond in O2 is much weaker than other double bonds or pairs of single bonds, and hence the formation of the stronger bonds in the combustion products CO2 and H2O result in the release of energy.

The chemical equation for the combustion

The reaction commonly emits heat and lights both. The usual equation for a complete combustion reaction is CH₄ + O₂ → CO₂ + H₂O.

Types of Combustion Reaction

Complete Combustion Reaction

In this process, the reactant burns in oxygen and produces a limited number of products. When a hydrocarbon burns in the presence of oxygen, the reaction will primarily yield carbon dioxide and water. When elements burn, the products are primarily the most common oxides.

Incomplete Combustion Reaction

This type of reaction occurs when there is short of oxygen to allow the fuel to react completely to produce carbon dioxide and water. It also occurs when the combustion is quenched by a heat sink, such as a solid surface or flame trap.

Carbon, carbon monoxide, and/or hydroxide is produced instead of carbon dioxide. Carbon monoxide causes headache, dizziness, vomiting, and nausea. It is also very harmful to our environment.

Smoldering Reaction

It is a type of combustion reaction which is often slow. Also, it has low-temperature, and flameless, sustained by the heat evolved when oxygen directly attacks the surface of a condensed-phase fuel. It is a typically incomplete combustion reaction.

Example, initiation of residential fires on upholstered furniture by weak heat sources (e.g., a cigarette, a short-circuited wire).

Spontaneous Reaction

It is a type of combustion, which occurs by self-heating, followed by thermal runaway and finally, ignition. For example, phosphorus burns at room temperature without the application of heat.

Rapid Reaction

As the name suggests it is a fast combustion reaction, with the release of large amounts of heat and light energy, which often results in a flame. For example, Fire which releases both heat and light.

Turbulent Reaction

This type of combustion resulting in a turbulent flame is most in use for industrial application.

Micro-Combustion Reaction

The Combustion which happens in very small volumes is micro-combustion.

Micro-Gravity

It refers to a “Low” gravitational state to such a level that the influence of buoyancy on physical processes is comparatively small relative to other flow processes that are present at normal gravity.

However, in this kind of environment, the thermal and flow transport dynamics usually behaves quite differently than in normal gravity conditions (e.g., a candle’s flame takes the shape of a sphere).

Reaction Mechanism

The entire combustion reaction-taking place in oxygen is a chain reaction in which many distinct radical intermediates participate. The great energy required for initiation is explained by the unusual structure of the dioxygen molecule.

The less-energy configuration of the dioxygen molecule is a stable, relatively unreactive diradical in a triplet spin state. Most of the fuels are usually in a single state, with paired spins and zero total angular momentum.

To kick-start the combustion, energy is required to force dioxygen into a spin-paired state, or singlet oxygen. This intermediate is extremely reactive. It supplies the energy as heat, and the reaction then produces additional heat, which allows it to continue.

In the case of hydrocarbons, the hydrogen atom abstraction (not proton abstraction) initiates the reaction from the fuel to oxygen, to give a hydroperoxide radical (HOO). This HOO reacts further to give hydroperoxides, which break up to give hydroxyl radicals.

Pyrolysis reactions take place in solid and heavy liquid fuels that give more easily oxidized, gaseous fuels. All these reactions are endothermic and require constant energy input from the ongoing combustion reactions.

Examples of Combustion Reaction

• Burning of any kind of Wood or Coal to heat your home.
• Car and buses burn petrol or diesel to run.
• Natural Gas or LPG is in use on your stovetop. Combustion of these gases helps in cooking.
• For the production of energy in thermal power plants.
• Fireworks
• Combustion of butane (commonly found in lighters).

Solved Questions for You

Q.1. How do you know when a combustion reaction is complete?

Ans: Combustion requires three things to occur: fuel (hydrocarbons), oxygen (from the air), and a catalytic spark. Complete combustion on its completion will produce only carbon dioxide and water as the products and nothing will be leftover.

However, incomplete combustion will produce other byproducts like carbon monoxide or carbon soot left behind.

Q.2. Who discovered combustion?

Ans: French chemist Antoine-Laurent Lavoisier discovered in 1772 that the products of burned sulfur or phosphorus—in effect their ashes—outweighed the initial substances, and he postulated that the increased weight was due to their having combined with air.