As most of us know, fire is the rapid oxidation of material in combustion which release light, heat and other reaction products (usually the oxides of the consituent elements in the material) According to wikipedia: Combustion is an exothermic chemical process between a fuel and an oxidant (usually oxygen) which convert the fuel into heat and other byproducts I'm not sure whether you have came across this before. Some games such as The Legend of Zelda: Ocarina of Time and Powder Toy has a weird idea of a cold flame, a flame which emits visible (usually blue) light but absorbs heat instead of relesing it, therefore generates a flame which freeze instead of heat things. Similar concept (the freezing beam) is also found in countless video games; however ordinary laser can already provide the cooling effect via laser cooling (though to things the size of small molecules or below) Trying to mess with the Gibbs free energy equation G(p,T) = H − TS provide one possible condition where a spontaneous 'endothermic combustion' will occur H<0, T>0, S>0. (S<0 is not preffered as entrophy tend to increase according to the second law of thermodynamics) But I'm not sure whether the T depends on H. In additon a discussion with my chemistry teacher said a subtance with a ΔH[sub]c[/sub][sup]0[/sup] < 0 simply cannot burn and that reversing the sign of ΔH[sub]c[/sub][sup]0[/sup] is simply the ΔH[sub]f[/sub][sup]0[/sup] for some substance As I cannot find any proof to disprove the idea that such a cold flame is impossible (search engines gives me headaches). Is there any way without violating known laws of physics to produce it or something with similar properties OR is there any formal proof to show that the above is impossible with known laws of physics? P.S. Like the previous thread, I'm not sure whether the above idea/fabrication is considered as a crank or not
I've never seen anything with the properties that would nessesary to accomplish this, but its not like I've seen everything. Glow sticks are a chemiluminescencent endothermic reaction but in liquid form. You would need the same kind of reaction that produces a lighter then air gas. However, it would have to be the gas that was giving off the light. This would look like a normal fire (or maybe a wierd colored fire lol) but it would not be hot, it may even feel cool to the touch. However, this would not be cold enough to freeze anything, it would only be good to give a cold fire illusion. Still though, I don't think anything has (or will have) this properties, but I could be wrong!
as belive said chemical proccesses could cause heat absorbsion, its not behond the relms of possibility that it could also put out light
Not what I said, chem lights are an endothermic (absorbs heat) chemical reaction and they make light. They are however a liquid and do not absorb heat to the extent needed.
Well at least it can absorb heat to the extent that it feels cool to the touch So if people can discover or artifically produce an endothermic reaction that produce light with gases, then it will already met the minimal requirement of a cold flame
I personally know that a cold flame (cool to the touch) is very possible. My exe's father was in a band and they paid thousands to some company in Japan that has developed pyrotechnics the burn at a cooling 60 F, so you're not crazy at all! He said that all he could tell was there was some sort a gas that was passed through a liquid coated with caution/hazard signs. The mist was then set aflame by a spark and channeled through a tube (for height). I hope this helps someone sleep at night, but I am sorry that I can't provide more info (like the chemical equation for the reaction).
Oxidation is an exothermic reaction. End of. You would need to invoke Maxwell's Demon to maintain an endothermic reaction. We just don't see such statistical events maintaining themselves.
oxidation isnt the only reaction that gives off light and thus a flame, thats the beauty of chemistry
it honestly doesnt matter. if the reaction can take place at 40 F and it only releases enough energy to raise it to 60 F then even though its exothermic, i would still call it a cold flame
Then you are abusing scientific terms. Such reactions are exothermic, and give off heat. That's HEAT. Not cold. HEAT. do I need to say it again?
if you want to be like that, then i could argue the fact that there is no such thing as cold in the first place
You'd be right, cold is defined as the absence of heat. Therefore it technically doesn't exist except as a concept we use to help define the world in simple terms.
Hot and cold are relative terms, they are meaningless when only one object is involved e.g. 100[sup]o[/sup]C steam is hot relative to us (37[sup]o[/sup]C) but cold relative to a ~1000[sup]o[/sup]C molten iron Whereas for heat, it is defined in physics as "the transfer of energy" I think that will be sufficient cause my minimal requirement for a cold flame is "a flame that is cool to the touch" Any actual chemical reactions that can do that?
Flames are exotherrmic reactions, releasing heat. So the system is hotter while the flame is present than before the reaction was initiated. The only relative measure is that of the system, and it's immediate environment. Introducing some arbitrary 3rd party relative measure is pointless. Let us consider the activation of this reaction,... if it were colder than it's environment while running, it must have a huge activation energy to start it off, or the ambient temperature, being greater than it's running temperature would initiate it, wouldn't it? Consider the reaction kinetics of that for a moment,... does it fly? No.
Hmm Do you mean for this type of reaction occur Either huge amount of energy is supplied to the system to overcome the activation energy barrier? Or that it will start spontaneously if the activation energy is lower than the energy supplied by the surrounding environment? And that because it is colder than the amibient temperature, it cannot sustain and soon stops? (Too bad I have not learnt much about the kinetics of chemical reactions, thus I don't really sure how to analyse)
Assuming two gasses (or even liquids in aerosol) can be found which react endothermically and luminesce, it would be possible to produce something which looked something like a flame, although it might not float upwards the way flames do. You couldn't properly call it a flame though, because that word refers to combustion reactions. It would be a contradiction in terms. As a matter of artistic license that would be okay, but it's not a good basis for descriptions or understanding of the actual world.
