What is Combustion? Fire is a chemical chain reaction which takes place with the evolution of heat and light. In order for a fire to take place there are 3 main ingredients that must be present: Oxygen, Heat and Fuel.  In chemistry we call the type of reaction that produces fire a combustion reaction. Combustion is a high-temperature exothermic (heat releasing) redox (oxygen adding) chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Whenever we complete a combustion reaction a hydrocarbon (compound of C and H) there are generally the same products formed: CO2 and H2O. Example The fuel you burn in your car's engine contains octane, C8H18. When octane is burned, the products are CO2 and H2O. 2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(g) The key ingredient to the process is the availability of oxygen. Combustion cannot take place in an atmosphere devoid of oxygen. So if you have a bottle of gasoline (octane) sitting around and open to the atmosphere which contains oxygen, why doesn�t it just burst into flames? The answer to this question is the need to overcome the activation energy of the reaction, which means that it requires energy at first to "jump start" the process. In your car, the distributor and battery provide this starting energy by creating an electrical "spark". Other sources of initial energy can come from the Sun, matches, friction, etc. The combustion reaction itself is quite exothermic. Extreme Whoosh Bottle Trio When heat is produced in the process of a chemical reaction this is known as an Exothermic Reaction. Example N2 + 3H2 → 2NH3 + Heat C + O2 → CO2 + Heat When heat is absorbed from the reacting substances this is known as an Endothermic Reaction. Example 2C + H2 - Heat → C2H2 3O2 - Heat → 2O3 But remember, whether endothermic or exothermic, both types of reactions still require an Activation Energy to begin.
Updated May 16, 2018 By Doug Bennett
Combustion describes a chemical process whereby rapid oxidation produces heat. In everyday terms, it’s the process that produces heat on a cold evening when you light a fire in the fireplace. Combustion requires three things to occur: an initial ignition source, such as a match; fuel, such as firewood; and an oxidant, aka oxygen. Combustion results in a number of products: in the case of organic combustion, carbon dioxide, water and energy.
In combustion, chemical bonds are broken and new bonds form. Energy is required to break the molecular bonds: the endothermic part of the process. When new bonds form, meanwhile, energy is released: the exothermic part of the process. If the overall process produces more energy than it uses, the sum of the process is exothermic and produces energy as heat or heat and light. If a material produces an exothermic reaction, it is said to be combustible.
As noted, every combustion process requires an initial influx of energy to break the first bonds. An ignition source, such as a spark or flame, provides this energy. Once the combustion process begins producing energy (exothermic), the combustion process continues until it completely consumes either the fuel or the oxidant. In other words, an exothermic process is self-supported once initiated.
The first required reactant in combustion is a fuel. Many of these fuels, called combustibles, are organic. Organic materials contain carbon, hydrogen and oxygen. However, some inorganic materials, such as magnesium, are also combustible. The second required reactant in combustion is an oxidant. Oxygen is the universal oxidant and required for all combustion. Combustion will not occur without both of these reactants. Remove the fuel from a fire and it goes out. Likewise, remove the oxidant – by smothering the flames – and the fire also goes out. This is the purpose behind fire extinguishers.
The combustion of organic materials creates a number of products. The first product of organic combustion is carbon dioxide. The second product of organic combustion is water, typically released as water vapor. The third product of organic combustion is energy, released as heat or heat and light. Because there are other molecules present in most fuels, the combustion process is not entirely clean. This means it produces small amounts of other materials, many of which are potentially harmful. Inorganic combustion does not produce carbon dioxide or water. For example, when magnesium (fuel) reacts with oxygen (oxidant), the result of the combustion process is magnesium oxide and heat. The one constant in combustion, regardless of the fuel, is the release of energy as heat or heat and light.
In order to continue enjoying our site, we ask that you confirm your identity as a human. Thank you very much for your cooperation. Roasting marshmallows over an open fire is a favorite past-time for campers, outdoor cook-outs, and just gathering around a fire in the back yard. The trick is to get the marshmallow a nice golden brown without catching it on fire. Too often we are not successful and we see the marshmallow burning on the stick – a combustion reaction taking place right in front of us.
A combustion reaction is a reaction in which a substance reacts with oxygen gas, releasing energy in the form of light and heat. Combustion reactions must involve \(\ce{O_2}\) as one reactant. The combustion of hydrogen gas produces water vapor: \[2 \ce{H_2} \left( g \right) + \ce{O_2} \left( g \right) \rightarrow 2 \ce{H_2O} \left( g \right)\nonumber \] Notice that this reaction also qualifies as a combination reaction. The Hindenberg was a hydrogen-filled airship that suffered an accident upon its attempted landing in New Jersey in 1937. The hydrogen immediately combusted in a huge fireball, destroying the airship and killing 36 people. The chemical reaction was a simple one: hydrogen combining with oxygen to produce water. Many combustion reactions occur with a hydrocarbon, a compound made up solely of carbon and hydrogen. The products of the combustion of hydrocarbons are carbon dioxide and water. Many hydrocarbons are used as fuel because their combustion releases very large amounts of heat energy. Propane \(\left( \ce{C_3H_8} \right)\) is a gaseous hydrocarbon that is commonly used as the fuel source in gas grills. \[\ce{C_3H_8} \left( g \right) + 5 \ce{O_2} \left( g \right) \rightarrow 3 \ce{CO_2} \left( g \right) + 4 \ce{H_2O} \left( g \right)\nonumber \]
Ethanol can be used as a fuel source in an alcohol lamp. The formula for ethanol is \(\ce{C_2H_5OH}\). Write the balanced equation for the combustion of ethanol.
Step 1: Plan the problem. Ethanol and oxygen are the reactants. As with a hydrocarbon, the products of the combustion of an alcohol are carbon dioxide and water. Step 2: Solve. Write the skeleton equation: \[\ce{C_2H_5OH} \left( l \right) + \ce{O_2} \left( g \right) \rightarrow \ce{CO_2} \left( g \right) + \ce{H_2O} \left( g \right)\nonumber \] Balance the equation. \[\ce{C_2H_5OH} \left( l \right) + 3 \ce{O_2} \left( g \right) \rightarrow 2 \ce{CO_2} \left( g \right) + 3 \ce{H_2O} \left( g \right)\nonumber \]
Combustion reactions must have oxygen as a reactant. Note that the water produced is in the gas state, rather than the liquid state, because of the high temperatures that accompany a combustion reaction. Summary
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What two reactants are necessary in order for a hydrocarbon combustion reaction to take place?
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