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Magical fire is often depicted as flames. To get fire and flames the right mixture of oxygen, fuel and heat is needed. Assuming that the magic only provides the heat, there are only two chemical reactions that could explain the flames. The nitrogen in the air reacts with oxygen to form nitric oxide:

$$\mathrm{N}_2 + \mathrm{O}_2 \to 2\mathrm{NO}$$

and nitrogen dioxide:

$$\mathrm{N}_2 + 2\mathrm{O}_2 \to 2\mathrm{NO}_2$$

Judging by the fact that we're all still alive, it must be quite hard to get these reactions started. What does this tell us us about fire magic with flames? How hot is it? What color would the flames have? Is the reaction endo- or exothermic?

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  • $\begingroup$ A flame is just very hot air, nothing more. $\endgroup$
    – AlexP
    Jan 2 '20 at 0:08
  • $\begingroup$ If it IS a chemical reaction in the atmosphere between nitrogen and oxygen, it pretty much has to be endothermic. If it's exothermic, it'll be self-sustaining and will spread across the entire world and kill everyone. $\endgroup$
    – Ryan_L
    Jan 5 '20 at 1:52
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You don't necessarily need a chemical reaction to have visible flames. Most of the light released by fire is due to black body radiation, the heat given off by anything hot. The color of black body radiation depends on exactly how hot the material is. Red is cool, blue is hot. This is true regardless of what the material is. Iron glows the same color as sodium and as helium if all 3 are at 1000 degrees. The common shape and motion of flames is just due to convection currents. Again, all you need is heat, regardless whether it comes from a chemical reaction, a laser, or magic.

Some chemical reactions do produce their own colors, but I can't help you there. Maybe someone else can.

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Magical fire could be “simpler” in concept. Magic takes oxygen and sunders it into 8 hydrogen atoms. That process itself takes magical energy from the caster. But one you have free hydrogen (H) atoms, science takes over: the hydrogen atoms react with the remaining oxygen (O2) almost instantly to produce a huge dump of energy and water (H2O) as a byproduct.

Hydrogen burning in air burns at about 2000 deg Celsius (very exothermic). Hydrogen burns with a pale blue flame that is nearly invisible in daylight. The flame may appear colored if there are impurities in the air.

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

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  • $\begingroup$ Why not use the massive amount of energy required to split the oxygen atoms and use it directly to heat the air? The energy released by a chemical reaction is vastly inferior to the energy required to break the oxygen nucleus. $\endgroup$
    – AlexP
    Jan 1 '20 at 22:50
  • $\begingroup$ @AlexP I assume magic does things science can’t, like cheap fission. Like some sort of mechanical advantage. My usual approach to questions like these is to identify the physical effect that magic contributes that science cannot that does what the questioner wants. In this case, produce realistic flame from non-flammable source in a way consistent with chemistry. $\endgroup$
    – SRM
    Jan 1 '20 at 23:45
  • $\begingroup$ @AlexP put another way: science needs lots of energy to split atoms. Magic doesn’t cost that much to do the same, for whatever reason. $\endgroup$
    – SRM
    Jan 1 '20 at 23:47
  • $\begingroup$ All I'm saying is that a very small fraction of the amount of energy required to split oxygen nuclei would do quite well to heat the air to the temperature of a flame... A flame is just very hot air, after all. $\endgroup$
    – AlexP
    Jan 2 '20 at 0:07
  • $\begingroup$ @AlexP But what I’m saying is the caster doesn’t have enough energy to split an atom. Sure, if they had that energy, use it directly. But that’s an immense amount of energy. Magic subs that out. Some small amount of magic — cantrip level — is all that is needed to create flame. $\endgroup$
    – SRM
    Jan 2 '20 at 1:34
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Depending on the exact properties of magic in your world, there may be various methods of performing fire magic...

Basing the magic mostly on real life physics, you'd need three items to create fire:

  • Heat or energy
  • Fuel
  • An oxidiser

I'll try to describe what would be theoretically nescessary in the context of magic - so i'll put it into an example of making a basic fireball or flamethrower-like spell. Though i'll also put in the limit that the wizard won't have to carry extra ingredients with him in order to create said spell - that is, he can only use the components of the same air he breathes.

So, let's start with a nitrogen reaction as OP describes...

The nitrogen in the air reacts with oxygen to form nitric oxide:

N2+O2→2NO

and nitrogen dioxide:

N2+2O2→2NO2

Provided that magic only creates the heat, you'd need a lot of energy to make this happen - likely beyond whatever energy output a normal living being could ever provide. Especially if the magic does not provide a way to contain the reaction with some manner of telekinesis

First off, you face the main problem of having to split an atmospheric dinitrogen molecule into individual nitrogen atoms. Dinitrogen molecules are, however, bound together with a very strong triple molecular bond. One of the few forces of nature that is able to break that bond is electricity, and a lot of it - in the form of lightning.

So, in this context, along with creating a telekinetic enclosed space, the wizard could use the nitrogen as fuel, a lightning spell as energy source, and oxygen as the oxidiser.

Then again, using nitrogen in the reaction wouldn't likely produce a fireball, even with extra oxygen added to the telekinetic "container". If that were the case, even a small fire could burn off the entire atmosphere.

On the other hand, if the mage has molecular reconstitution in his portfolio of magical abilities - he could easily create something like dicyanoacetylene (C4N2), which can burn at almost 5000 degrees C with a bright, white-bluish flame...

Provided that magic could also provide a weak electrical field, the wizard could utilize water vapor that is suspended in the air. Using the electrical property of magic, along with aforementioned telekinetic "container", the wizard could concievably create and regulate a bubble of hydrogen-oxygen mix (as well as various dust particles to make the fire visible) and ignite it with wither a spark (~20 microjoules) or sufficient heat (around 570 degrees C).

Not only is hydrogen combustible, the spell could also be regulated to have an explosive effect. It can also react with the atmospheric nitrogen to produce NOx gasses, as well as nitrogen-hydrogen compounds like ammonia

So, to answer the questions:

What does this tell us us about fire magic with flames?

I'd say, that like in alot of electrical devices, you'd have to "cheat"; using a nitrogen reaction alone, would be prohibitively expensive on its own.

Our mage would have to use other means to create the desired reaction.

Also, if magic can only provide heat in and upon itself, simply warming a spot of air would be unlikely to create the reaction, unless our mage is able to contain and heat the air to plasma. However, a common property of magic is that it's considered a form of energy. Provided that our mage can conjure at least some degree of electrical current, this already provides a good shortcut.

You do forget one thing with standard, day-to-day atmospheric air: You have the oxidiser, our mage has heat and energy - but the main constituent of the atmosphere - nitrogen (or rather dinitrogen molecules) - is not a suitable fuel source due to its normally inert nature.

Leveraging hydrogen, gained from electrolysing water vapor, would also carry the limitation of being nearly or completely unusable in dry environments unless the wizard were to carry a flask of water (steam -> electrolyse -> boom)

The key part is to raise the concetration of the desired element(s) in the telekinetic reaction bubble and keeping the reaction fed with fuel.

How hot is it?

Hydrogen can burn at up to 2,800 degrees C, provided the mage is skilled enough or able to provide enough hydrogen to create a stochiometric reaction with oxygen - that is a 2:1 mix of hydrogen-oxygen

What color would the flames have?

Pure hydrogen flames are a very deep blue and emit mostly ultraviolet light, that can just barely be seen in daylight - so a "pure" fireball would likely have the same bluish tinge.

The end colour can be regulated by our mage, however, as he has the freedom to include any kind of dust or particles in the reaction. This dust would likely create yellow-orange streaks in the fireball depending on the concentration. Our mage could also concievably regulate the temperature of the reaction - which in turn can regulate the colour.

Is the reaction endo- or exothermic?

Most, if not all burn/flame reactions are exothermic

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  • $\begingroup$ One of the few forces of nature that is able to break that bond is electricity, and a lot of it - in the form of lightning. And Volkswagen diesel engines, in the space of 1.6l worth of cylinders. So that they needed to cheat the emission tests. $\endgroup$ May 25 '20 at 1:06
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I am always interested in sciences related to magic in modern media. I actually read a book where the author demonstrated physical laws inherent in engineering and how the magic of the world seems to go against those basic rules and no one knows why. Though I will kind of say that you may not need a chemical reaction for fire magic, the movie the Sorcerer’s Apprentice demonstrated fire magic as the result of friction. I will say I think that line of thinking could open up a whole host of possibilities like sticking to the walls like Spider-Man, or have your enemies fail and fall like their trying to walk on an ice skating rink, just some food for thought. As for how hot magic fire can go, sorry as I can tell that always depends on how much juice you put into it. Hope the answers you get keep The creative juices flowing.

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