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?

  • $\begingroup$ well fire isn't really an actual thing, its the result of reaction giving out energy. $\endgroup$ – H.Linkhorn Dec 11 '18 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? $\endgroup$ – Dmitry Dec 11 '18 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 Dec 11 '18 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 Dec 11 '18 at 21:15
  • $\begingroup$ Paint drying is a different process. It is literal drying. $\endgroup$ – Jan Dec 12 '18 at 1:16

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.

  • $\begingroup$ 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? $\endgroup$ – Dmitry Dec 11 '18 at 20:02

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.

  • $\begingroup$ 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? $\endgroup$ – Dmitry Dec 11 '18 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 Dec 11 '18 at 20:15

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