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I have heard that chemical reactions create energy. I wanted to know how this energy was created (specifically light energy) and how this energy came about. I wanted to know if the energy produced was made of particles (for example, light energy is made of photons).

My answer I already knew about heat, kinetic, potential, and sound energy. What I was really looking for was light energy, which is caused by a phenomenon known as chemiluminescence.

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    $\begingroup$ Your question is a bit vague. There are many forms of energy and nearly all of them can be the result of a chemical reaction or interaction with chemicals. I'm also not sure I understand what you mean about your either/or: subatomic particles (e.g. electrons) play a pivotal role in chemical reactions, but "devoid of physical form" - I don't follow. $\endgroup$ – bobthechemist Jun 25 '13 at 23:58
  • $\begingroup$ Energy is usually expressed as a "wave" or other vague term. I'm asking for a precise explanation of what it is, and I want to know if the energy from a chemical reaction is a "wave" or if it's more tangible, like radiation. $\endgroup$ – person27 Jun 26 '13 at 16:15
  • $\begingroup$ @Stopforgettingmyaccounts... you seem to be very unclear on energy. Energy can be potential energy, which is basically due to interactions between particles. For example, if you keep two electrons close the energy is potential energy. Bond energy is another form of chemical energy. $\endgroup$ – ManishEarth Jun 27 '13 at 9:48
  • $\begingroup$ On the other hand, kinetic energy is due to the motion of particles. In this case, that's the radiation you talk of -- both electromagnetic (light, X-rays, infrared) radiation and from other particles like electrons (and the radiation you get from radioactive materials -- but usually this kind of radiation is different from radiation from a chemical reaction). $\endgroup$ – ManishEarth Jun 27 '13 at 9:49
  • $\begingroup$ Electromagnetic radiation has a wave nature, but you can look at it as a bunch of moving particles, too. $\endgroup$ – ManishEarth Jun 27 '13 at 9:49
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Usually it's radiation. Depending on how exotermic reaction was, in which medium was it done, result is light staring with infra-red up to v.short ultra-violet. You can't generate particles like electrons because the low of Charge conservation must be obeyed (you transferring the electrons from one substance to the other).

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Let's start off on common footing by making sure we understand the definition of energy:

Energy is the capacity to do work.

An object may have many types of energy, we'll get to those in a second, but the total energy of an object will be the sum of its kinetic energy and its potential energy. Kinetic energy is the energy associated with the movement of an object and potential energy is the energy associated with an object's position.

To take a physical example, hold out a book (preferably your heavy, expensive general chemistry textbook) and drop it on the floor (preferably, not on your little brother's toes). The book falls to the ground and a loud noise is heard. As the book moved, the potential energy stored in its original position was converted to kinetic energy as it fell to the ground. Upon hitting the ground the individual atoms that make up the book crashed in to the individual atoms that make up the ground, causing them all to move. This movement of atoms is thermal energy.

Let's focus on thermal energy for a moment, the majority of chemical reactions, including the combustion reactions you refer to, involve the transfer of thermal energy. Hold a cup of coffee in your hand; what happens to your hand? Assuming the coffee was hot, and your hand was not, your hand starts to feel warm. We might say your hand is heating up. This thing we refer to as *heat is the transfer of thermal energy; the molecules in the cup of coffee were bouncing around, crashing in to the cup, which made the molecules in the cup crash around hitting your hand.

So now let's turn to chemical energy which is the energy associated with the position of nuclei and electrons in atoms and molecules. Since we are talking about (relative) positions of objects, this energy is a form of potential energy. Some molecules, such as methane, have nuclei and electrons that are positioned in such a way that they store a large amount of potential energy. When the positions of these nuclei and electrons are moved, potential energy is converted into kinetic energy.

So in summary, the energy of chemical reactions is best described in terms of potential and kinetic energy, or in other words the relative position and movement of nuclei and electrons. Often, the energy we experience in chemical reactions can be adequately described by the transfer of heat, and therefore thermochemistry and thermodynamics take up a large portion of our instruction in Chemistry. Other types of energy, such as electromagnetic radiation, electrochemical, and nuclear, can all be described in terms of potential and kinetic energy, namely the position and movement of objects.

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  • $\begingroup$ Thanks. It was actually light energy that made me want to ask the question. I knew that it was made of photons and couldn't figure out why or how it came from chemical reactions. But I did under the term 'chemiluminescence' on Wikipedia. $\endgroup$ – person27 Jun 28 '13 at 16:54
  • $\begingroup$ @Stopforgettingmyaccounts... you might want to edit your question a bit to reflect where it came from. Your example of a combustion reaction causes a bit of confusion. $\endgroup$ – bobthechemist Jun 28 '13 at 18:00

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