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Combustion

6) Combustion – similar to decomposition reaction, except that oxygen and heat are required for it to occur.

Oxygen combines with a carbon compound to form water and CO2.

Exothermic (heat producing)

Napthalene burning: C10H8 + 12 O2 —> 10 CO2 + 4 H2O

Cellular respiration (body temp burning of sugar)

C6H12O6 + 6O2   6CO2 + 6H2O + [energy stored in ATP]

Combustion of methane gas: CH4 + 2O2 CO2 + 2H2O

http://www.iun.edu/~cpanhd/C101webnotes/chemical%20reactions/combustion.html

http://www.chemteam.info/Equations/Combustion.html

Hydrocarbons can combust (burn in the presence of oxygen)

https://cedarbraechemistry.wikispaces.com/5.1+Thanoja-+Combustion+of+Hydrocarbons https://cedarbraechemistry.wikispaces.com/5.1+Thanoja-+Combustion+of+Hydrocarbons

There are many combustible fuels

https://cedarbraechemistry.wikispaces.com/5.1+Thanoja-+Combustion+of+Hydrocarbons https://cedarbraechemistry.wikispaces.com/5.1+Thanoja-+Combustion+of+Hydrocarbons

Burning oil, paper or wood is almost never complete. There is always incomplete combustion.

Incomplete versus complete combustion

http://www.glogster.com/amackay/complete-incomplete-combustion/g-6ln813kfgc0eu8o4vai8sa0 http://www.glogster.com/amackay/complete-incomplete-combustion/g-6ln813kfgc0eu8o4vai8sa0

As such, one ends up with millions of different complex carbon molecules, collectively called “soot”.

Soot from a smokestack

https://californiaac.wordpress.com/2015/02/19/what-is-soot/ https://californiaac.wordpress.com/2015/02/19/what-is-soot/

Soot, or ash (product of fire, incineration or combustion)

http://web.extension.illinois.edu/stain/staindetail.cfm?ID=140 http://web.extension.illinois.edu/stain/staindetail.cfm?ID=140

Soot molecules formed from smaller molecules, like PAH

PAH = polycyclic aromatic hydrocarbons.

Organic compounds containing only C and H, and multiple aromatic rings.

http://wiki.gekgasifier.com/w/page/6123815/Soot%20Formation%20Chemistry http://wiki.gekgasifier.com/w/page/6123815/Soot%20Formation%20Chemistry

Other forms of soot molecules

http://pubs.rsc.org/en/content/articlelanding/2000/gt/b004601i#!divAbstract http://pubs.rsc.org/en/content/articlelanding/2000/gt/b004601i#!divAbstract

How do these reactions occur?

Single-replacement reactions, and combustion reactions, occur when one of the compounds oxidizes (loses electrons), and another compount is reduced (gains electrons.) These are called ReDox reactions and are studied in electrochemistry: ReDox reactions

What is fire made of?

This depends on the type of fuel involved in the combustion

Example: Burning candle.

The applied heat causes the fuel molecules in the candle wax to vaporize. In this state they can then readily react with oxygen in the air, which gives off enough heat in the subsequent exothermic reaction to vaporize yet more fuel, thus sustaining a consistent flame. The high temperature of the flame causes the vaporized fuel molecules to decompose, forming various incomplete combustion products and free radicals, and these products then react with each other and with the oxidizer involved in the reaction. Sufficient energy in the flame will excite the electrons in some of the transient reaction intermediates such as:

Methylidyne radical (CH)

Diatomic carbon (C2)

In most fires, most of the glowing gas is heated:

carbon dioxide

carbon monoxide

water vapor

oxygen

– Flame. (2016, November 22). In Wikipedia, The Free Encyclopedia

https://en.wikipedia.org/wiki/Flame

Also see The Chemistry and Physics of Fire: Encyclopedia of Occupational health and safety

Is fire a plasma?

accorsing to this common explanation, “Yes”… but there is a reason to believe that this explanation is mistaken. Can flame be “Plasma”? – Arrow of Time

All gases have some tiny amount of ionization, so that in of itself doesn’t qualify any gas to be called a plasma.

See this further discussion  https://www.quora.com/What-is-fire-What-are-the-physics-of-fire

 

Color of flames

Why Are There Blue and Green Flames? By Steven Dutch

Learning standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

8.MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

HS-PS1-2. Use the periodic table model to predict and design simple reactions that result in two main classes of binary compounds, ionic and molecular. Develop an explanation
based on given observational data and the electronegativity model about the relative
strengths of ionic or covalent bonds.
Clarification Statements:
• Simple reactions include synthesis (combination), decomposition, single
displacement, double displacement, and combustion

 

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