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I woke up today with a question of what is fire; looked up the definition and the first response was that fire was rapid oxidation.

I was curious what the difference was between rapid oxidation and regular oxidation that we have all around us as seen with metals rusting, book pages yellowing, artificial aging, paint drying, apples browning due to air exposure.

I cannot find an answer to what the difference between rapid and regular oxidation is, other than the speed of the reaction, and the visibility of the reaction when it becomes fast enough.

I am curious whether there is any difference at all between metals "rusting", paper "burning"/"aging", paint "drying", or if these are all different names for the same process at different rates.

Is it reasonable to say that there is fire everywhere there is oxidation occuring, but it's invisible until the reaction is fast enough?

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  • $\begingroup$ well fire isn't really an actual thing, its the result of reaction giving out energy. $\endgroup$
    – H.Linkhorn
    Commented Dec 11, 2018 at 19:22
  • $\begingroup$ From what I understand, fire is an actual thing in that if we have two universes, one with oxidation occuring, and one without oxidation occuring, and get temperature of the two universes at every point in space, then subtracting the gradient of the universe without oxidation occuring from the one with oxidation occuring will result in a gradient where the differences may be hot enough to suggest that the point/cluster of points in space is emitting visible light via thermal radiation, in which case we would call fire. Is this a valid model? $\endgroup$
    – Dmytro
    Commented Dec 11, 2018 at 19:27
  • $\begingroup$ With regards to what you are looking at i am unsure. But the traditional yellow flame that we could see when you burn paper is simply the excitation and then de-excitation of carbon atoms. $\endgroup$
    – H.Linkhorn
    Commented Dec 11, 2018 at 19:29
  • $\begingroup$ Oxidation of paper, apples, polymers, etc. goes selectively. You have chemical substances or regions of molecules which tend to oxidize and those that not. Combustion goes indiscriminately. You have a bond - it will be broken with suitable fire. $\endgroup$
    – Kelly Shepphard
    Commented Dec 11, 2018 at 21:15
  • $\begingroup$ Paint drying is a different process. It is literal drying. $\endgroup$
    – Jan
    Commented Dec 12, 2018 at 1:16

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Oxidation is a category of processes that increases the number of bonds to oxygen in a molecule.

Combustion(most fire) is a type of oxidation that happens really really fast and rather than just adding some extra oxygen generally turns the organic molecules into carbon dioxide(with some carbon monoxide due to incomplete combustion), and Water.

The most obvious example of this is when iron catches fire (requires heat and or high oxygen content in the atmosphere) it turns into the same Iron Oxide as rust, which is oxidation, but does so much much more rapidly, and generally due to the rapid runaway nature of the reaction, leads to much more damage to the macroscopic structure.

-Source am professional chemist, Learned this in the first year of my chemistry degree and regularly oxidize and occasionally combust samples in the course of my daily work.

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At the room temperature molecules doesn't have enough energy to pass the activation barrier for the process of turning everything into CO2 and water. This is why combustion never happens without initial heating Hope it helps.

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  • $\begingroup$ are you claiming that slow oxidation, given any amount of time, will never be able to accumulate the effects equivalent to rapid oxidation? And if so, is there still technically a "fire" at the point in space where oxidation is occuring, since oxidation emits heat, would there technically still be a visible light emitted from this point in space, no matter how dim, that would look like fire if amplified? $\endgroup$
    – Dmytro
    Commented Dec 11, 2018 at 20:02
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Rapid oxidation- burning - leads to two main products carbon dioxide and water. You cannot keep any records if paper is burned. In case of slow oxidation some of paper components are oxidized which changes the colour of paper, but just that. Old manuscripts can be stored for hundred of years if no none burns them.

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  • $\begingroup$ But wouldn't that be the same case if the fire under which the paper was uniformly burnt at a rate so slow as to not be able to burn the paper in hundreds of years? Wouldn't the paper still turn black/burnt given a significantly longer period of time? $\endgroup$
    – Dmytro
    Commented Dec 11, 2018 at 19:44
  • $\begingroup$ No. as the point of burning it is that you are supplying the paper with enough energy for complete oxidation. whist when just leave it, there isn't enough energy for complete oxidation to take place. $\endgroup$
    – H.Linkhorn
    Commented Dec 11, 2018 at 20:15

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