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avicenna
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Is it possible that in combustion, the chemical energy of reaction is released wholly through photon emission. Say as in simple burning of wood.
Not when you burn iron slowly, at a low temperature. Then it forms a rust-red oxide that has higher volume, that forces things apart. The colour in reflected light changes, but it does not emit photons.avicenna said:Is it possible that in combustion, the chemical energy of reaction is released wholly through photon emission.
Think of a candle. There are at least two distinct regions of emission: blue and yellow. Thie blue light is direct emission from from electronic transitions as the vaporized hydrocarbons convert to water and carbon dioxide and particulate carbon. This hot mix of gasses and particulates is buoyant and flows upward. The particulate carbon is hot enough (and large enough) to glow as a black body and at >2000K producing a very bright yellow emission. Your eye is sensitive to the yellow.avicenna said:Say as in simple burning of wood
OK. I will restrict it to simply burning carbon in oxygen giving CO₂. Let's assume there is no initial kinetic energy in the carbon and oxygen molecule. Then, somehow they combine to form CO₂. In what energy form is the combustion reaction energy released if not wholly as radiation photon.russ_watters said:The question sounds a bit unclear to me, but I was under the impression that most of the energy of combustion is usually in molecular motion. The combustion products are hot.
Thanks. This is the closest I get; I will examine further. Can I say the chemical energy is converted first wholly to radiation photon.hutchphd said:Think of a candle. There are at least two distinct regions of emission: blue and yellow. Thie blue light is direct emission from from electronic transitions as the vaporized hydrocarbons convert to water and carbon dioxide and particulate carbon. This hot mix of gasses and particulates is buoyant and flows upward. The particulate carbon is hot enough (and large enough) to glow as a black body and at >2000K producing a very bright yellow emission. Your eye is sensitive to the yellow.
Flame dynamics happen at many scales.
Then you don't have combustion. You need a spark (or something similar) to initiate the process. What you get after is basically a domino effect of hot, combusting material initiating the combustion of adjacent material.avicenna said:Let's assume there is no initial kinetic energy in the carbon and oxygen molecule.
Absolutely not! It is the other way around. The chemical reaction of combustion will result in hot, excited molecules that then d'excité by emission of radiation.avicenna said:Can I say the chemical energy is converted first wholly to radiation photon.
Can you explain this. Burning of firewood/coal will released chemical energy which is converted to heat which is basically kinetic energy of the molecules. The only mechanism which transfers kinetic energy between two molecules is collision. So which of the molecules first get the increased in kinetic energy and how.DrClaude said:Then you don't have combustion. You need a spark (or something similar) to initiate the process. What you get after is basically a domino effect of hot, combusting material initiating the combustion of adjacent material.
Absolutely not! It is the other way around. The chemical reaction of combustion will result in hot, excited molecules that then d'excité by emission of radiation.
Can you be more specific. There is a continuous conversion of chemical energy to heat.tech99 said:This is called the initiation energy. We have to break a few bonds to initiate the reaction, as when lighting a fire.
Note that the definition of "heat" is thermal energy transfer. Heat is not itself a type of energy. The conversion here is chemical energy to kinetic energy (i think for most fires...) and different chemical energy (excited electron state or ionized).avicenna said:Can you be more specific. There is a continuous conversion of chemical energy to heat.
Fundamentally, a quantum step generates photons with a quantised energy, plus or minus a variable thermal broadening of the individual photon energy.avicenna said:By just saying chemical energy gets converted to thermal energy explains nothing of the actual mechanism.
avicenna said:Please! Can someone tell other than the obvious. When you google for combustion, etc, you get hundreds of hits telling how in a wood fire or combustion, chemical energy is converted to thermal energy - whatever! But how? No one is telling the secret!
I have already said the only mechanism of kinetic energy exchange between two molecules is collision - no others. So please give some details how the chemical energy get magically transformed to thermal energy - or whatever energy you call it.
By just saying chemical energy gets converted to thermal energy explains nothing of the actual mechanism.
At least you say `the complete detail immensely complicated'. So I would not enquire further.hutchphd said:The mechanism that allows the molecules and atoms to maintain a stable configuration is called Quantum Mechanics. The system (say a candle in this case) is moving from higher energy states to lower energy states in a complicated way. The candle (wax +wick) had more energy than the final candle nib. The energy has been carried away by EM field and various constituent gas atoms and particulates which have left the area.Quantum Mechanics for the system describes it all, with the complete detail immensely complicated. That is the magic and even the simplest system will be beyond your understanding
QED.
I did not say that to dissuade your inquiry but rather to indicate there is no general complete answer to your question. As usual everyone lives with an approximation sufficient to his or her requirements and your requirements are not clear !avicenna said:So I would not enquire further.
I have no complaints at all about your replies. Your comments are fair, that the one word "combustion" involves many levels of difficulties. I don't ask further as I have no knowledge of QM.hutchphd said:I did not say that to dissuade your inquiry but rather to indicate there is no general complete answer to your question. As usual everyone lives with an approximation sufficient to his or her requirements and your requirements are not clear !
So the questions need specificity.
Seconded.DrClaude said:Quantum mechanics is definitely not necessary to understand combustion.
No, they don’t. Look at @DrClaude ’s diagram in post 22. Just as a ball sitting still in one valley won’t roll into the second valley (ignoring QM), a chemical species in one valley needs energy input to get to the second valley. This is called activation energy. For combustion reactions, the activation energy is smaller than the potential energy difference between reactants and products (IOW, the hill between the valleys is less tall than the altitudes of the valleys). This means that, once the reagents get over the energy hill (activation barrier), they go down to the second valley and have enough energy (be it translational/kinetic, rotational, vibrational, etc.) that they can give some of it to other reagents to help them over that hill. This is what makes combustion self-sustaining.avicenna said:Let's assume there is no initial kinetic energy in the carbon and oxygen molecule. Then, somehow they combine to form CO₂.
The equipartition theorem only applies to quadratic degrees of freedom, so it doesn't work for electronic energy. It also only works at equilibrium, which doesn't always apply (even locally) during combustion.avicenna said:Someone at stack exchange brought up equipartition of energy. So the chemical energy would be distributed to: translational KE, rotational KE, vibrational KE and some radiations.
Combustion energy is the energy released when a substance undergoes a chemical reaction with oxygen, producing heat and light.
Combustion energy is released through a chemical reaction called combustion, where a substance reacts with oxygen to produce heat and light. This reaction breaks the bonds between the atoms in the fuel and oxygen molecules, releasing energy in the form of heat and light.
The amount of combustion energy released depends on several factors, including the type and amount of fuel, the amount of oxygen present, and the efficiency of the combustion process.
The main source of combustion energy in most modern societies is fossil fuels, such as coal, oil, and natural gas. These fuels are burned in power plants, vehicles, and other industrial processes to produce energy.
Combustion energy is used in everyday life for a variety of purposes, including heating and cooking, transportation, electricity generation, and industrial processes. It is also used in the production of many everyday products, such as plastics, fertilizers, and pharmaceuticals.