Is fire a gas or not?

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Offline thedoc

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Is fire a gas or not?
« on: 09/12/2014 16:30:01 »
Mary asked the Naked Scientists:
   
Is fire a gas or not?

What do you think?
« Last Edit: 09/12/2014 16:30:01 by _system »

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Offline chiralSPO

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Re: Is fire a gas or not?
« Reply #1 on: 09/12/2014 16:35:48 »
Fire is not a substance. It is an exothermic chemical reaction that produces significant amounts of energy as heat and visible light. Fire usually occurs in the gas phase, but fire can result from the reaction of any combination of solids, liquids and gases, and some instances plasma can be produced in a flame.

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Offline PmbPhy

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Re: Is fire a gas or not?
« Reply #2 on: 09/12/2014 16:53:24 »
Quote from: chiralSPO
Fire is not a substance.
Of course fire is a substance. In fact its multiple substances. If the temperature of the flame is low enough then it's a gas. However sometimes the flames get so hot to be a different state of matter called a plasma. One dictionary defines a plasma as an ionized and macroscopically neutral gas with sufficient amount of free charges to make electromagnetic forces important to its macroscopic behavior. It is sometimes called the fourth state of matter.
« Last Edit: 10/12/2014 10:24:02 by evan_au »

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Offline chiralSPO

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Re: Is fire a gas or not?
« Reply #3 on: 09/12/2014 17:21:57 »
Just because fire HAS substance doesn't mean it IS a substance. Is a storm a substance? How about an avalanche? The definition of fire has nothing to do with the substances that it is made of, and everything to do with how they are behaving. There is no requirement on the composition of the flame, other than that there be an ongoing chemical reaction exothermic enough to cause incandescence. We can burn hydrogen and chlorine, or carbon disulfide and dinitrogen tetroxide (liquid-liquid combustion until it self heats to gaseous reactants and explodes). There is no substance that appears in both reactions, as reactant, intermediate or product. Even decomposition of single compounds can result in a flame (for instance low molecular-weight molozonides), so fires don't have to be the chemical reaction between two different compounds either. The important point is that a fire BURNS!
« Last Edit: 09/12/2014 17:23:30 by chiralSPO »

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Offline PmbPhy

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Re: Is fire a gas or not?
« Reply #4 on: 09/12/2014 17:41:05 »
Quote from: chiralSPO
Just because fire HAS substance doesn't mean it IS a substance.
In this case it is because fire is a thing (as much as a gas is a thing) whereas a storm is a state of nature and not the material of nature. Not so with fire. What I said holds in this case since my analogy was about things and not a state of being.

Please consider what I said and keep it in mind before you give an analogy like those above which don't apply. I.e. please look these things up in the dictionary and learn what the OP and others mean when they use a term such as this. I.e. in this case you were using a different definition of fire than the OP and I were. You were using the definition of fire as an oxidation process and I was using it as follows

http://www.merriam-webster.com/dictionary/fire
Quote
Fire - the light and heat and especially the flame produced by burning
« Last Edit: 09/12/2014 18:00:06 by PmbPhy »

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Offline lightarrow

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Re: Is fire a gas or not?
« Reply #5 on: 09/12/2014 19:23:21 »
Ok, I think it's just a matter of definition. The "flame" is certainly a substance, more specifically gaseous and hot (and probably with specifical motion too); the "fire" could be intended as a chemical process with a flame, ecc, or the flame + substances + light, or that substances involved. But I' mot an expert of english language, however.

--
lightarrow
« Last Edit: 09/12/2014 19:27:23 by lightarrow »

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Offline evan_au

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Re: Is fire a gas or not?
« Reply #6 on: 09/12/2014 19:46:07 »
To expand on the comment from lightarrow: In common usage,
  • A flame is made of glowing gas
  • A fire is composed of flame(s)

(chiralSPO gives some more extreme examples that might be more at home in rocket science than on your birthday cake!)

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Offline PmbPhy

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Re: Is fire a gas or not?
« Reply #7 on: 09/12/2014 19:58:48 »
To expand on the comment from lightarrow: In common usage,
  • A flame is made of glowing gas
  • A fire is composed of flame(s)

(chiralSPO gives some more extreme examples that might be more at home in rocket science than on your birthday cake!)
chiralSPO was talking about a related definition. I.e.
http://en.wikipedia.org/wiki/Fire
Quote
Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.
Here fire is a verb and not a noun. The OP was talking about fire as a noun. From the same page
Quote
The flame is the visible portion of the fire. If hot enough, the gases may become ionized to produce plasma.
Let us not begrudge chiralSPO his due. He merely wasn't paying close enough attention to what the OP wanted and forgot that nearly all words in the English language have multiple meanings.

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Offline David Cooper

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Re: Is fire a gas or not?
« Reply #8 on: 09/12/2014 21:27:19 »
The OP doesn't specify any meaning of "fire", and dictionary definitions are made by lexicographers rather than scientists, so many of their definitions are faulty and they should never be regarded as the final word on anything. I'm not sure that a fire is any different from a storm if you want to call it a substance. You can have a gas or plasma without fire, light emission without fire (glowsticks), glowing gas that isn't a flame (aurora), burning without flames (sun + magnifying glass + paper --> burned holes and smoke but often without flames), and chemical reactions that release heat without fire (as in our muscle cells). Fire is a process, but it can be referred to as a thing. A storm is a process too, but again it can be referred to as a thing (the storm hit us), and this is because any process can be referred to as a thing. Calling a storm a substance would be stretching things a bit too far though, and calling a fire a substance would be going too far too - it isn't a substance, even though substances are involved in it. The ancients thought it was a substance, of course (earth, air, fire and water), so there is a long tradition in calling it such, but science has moved on.

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Offline PmbPhy

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Re: Is fire a gas or not?
« Reply #9 on: 09/12/2014 21:51:09 »
Quote from: David Cooper
The OP doesn't specify any meaning of "fire", ..
When he said "Is fire a gas or not?" he clearly has the flame in mind rather than a chemical process. Teaching isn't always about taking what someone says literally but determining what they're trying to learn and in this case it's clear to me (although I understand not to you) that he has the flame in mind. That's always what I have in mind when I think of fire.

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Offline chiralSPO

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Re: Is fire a gas or not?
« Reply #10 on: 09/12/2014 22:49:37 »
The OP doesn't specify any meaning of "fire", and dictionary definitions are made by lexicographers rather than scientists, so many of their definitions are faulty and they should never be regarded as the final word on anything. I'm not sure that a fire is any different from a storm if you want to call it a substance. You can have a gas or plasma without fire, light emission without fire (glowsticks), glowing gas that isn't a flame (aurora), burning without flames (sun + magnifying glass + paper --> burned holes and smoke but often without flames), and chemical reactions that release heat without fire (as in our muscle cells). Fire is a process, but it can be referred to as a thing. A storm is a process too, but again it can be referred to as a thing (the storm hit us), and this is because any process can be referred to as a thing. Calling a storm a substance would be stretching things a bit too far though, and calling a fire a substance would be going too far too - it isn't a substance, even though substances are involved in it. The ancients thought it was a substance, of course (earth, air, fire and water), so there is a long tradition in calling it such, but science has moved on.

Preciously!

Quote from: David Cooper
The OP doesn't specify any meaning of "fire", ..
When he said "Is fire a gas or not?" he clearly has the flame in mind rather than a chemical process. Teaching isn't always about taking what someone says literally but determining what they're trying to learn and in this case it's clear to me (although I understand not to you) that he has the flame in mind. That's always what I have in mind when I think of fire.

Sometime the pupil asks a question and gets an unexpected response that opens their minds to a more complex and beautiful world.

I think flame and fire are essentially interchangeable when asking of their "substance," in either case calling fire/flame a gas would be an extreme oversimplification that overlooks the very essence of what fire is, which I think David Cooper describes quite eloquently (above). Is a human a solid or not?

Additionally, as there can be fires composed partly or entirely of matter in the plasma or liquid or even solid states, suggesting that a gaseous state is definitional would also be misleading.

Quote from: chiralSPO
Just because fire HAS substance doesn't mean it IS a substance.
In this case it is because fire is a thing (as much as a gas is a thing) whereas a storm is a state of nature and not the material of nature. Not so with fire. What I said holds in this case since my analogy was about things and not a state of being.

Please consider what I said and keep it in mind before you give an analogy like those above which don't apply. I.e. please look these things up in the dictionary and learn what the OP and others mean when they use a term such as this. I.e. in this case you were using a different definition of fire than the OP and I were. You were using the definition of fire as an oxidation process and I was using it as follows

http://www.merriam-webster.com/dictionary/fire
Quote
Fire - the light and heat and especially the flame produced by burning

If you can't see that a fire is more like a storm than a gas, you have some pondering to do!  [:)]
« Last Edit: 09/12/2014 22:53:51 by chiralSPO »

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Offline PmbPhy

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Re: Is fire a gas or not?
« Reply #11 on: 09/12/2014 23:30:01 »
Quote from: chiralSPO
If you can't see that a fire is more like a storm than a gas, you have some pondering to do!  [:)]
Actually its the other way around. A fire is often thought of as flames, and flames have substance to  them in the form of a gas. This isn't my first barbeque you know.

I  know that one of the definitions of "fire" is as a combustion process rather than a hot gas. However, from the way question was phrased, it's clear  that the OP was interested in the flame since he asked about the gas.
« Last Edit: 10/12/2014 10:23:29 by evan_au »

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Offline alancalverd

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Re: Is fire a gas or not?
« Reply #12 on: 10/12/2014 00:06:00 »
Of the various uses of the word as a noun, the Oxford English Dictionary offers just one that could be misconstrued as a gas: "A process in which substances combine chemically with oxygen from the air and typically give out bright light, heat, and smoke; combustion or burning:"

i.e. a process involving substances, not a substance. Like cookery.
helping to stem the tide of ignorance

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Offline jeffreyH

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Re: Is fire a gas or not?
« Reply #13 on: 10/12/2014 00:17:15 »
I wonder if the holographic principle has anything to say about flames. As for string theory how to spin networks fit in this case?
Fixation on the Einstein papers is a good definition of OCD.

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Offline PmbPhy

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Re: Is fire a gas or not?
« Reply #14 on: 10/12/2014 00:17:31 »
Quote from: alancalverd
Of the various uses of the word as a noun, the Oxford English Dictionary offers just one that could be misconstrued as a gas: "A process in which substances combine chemically with oxygen from the air and typically give out bright light, heat, and smoke; combustion or burning:"

i.e. a process involving substances, not a substance. Like cookery.
I disagree. This clearly cannot logically misconstrued as a gas since it clearly says "A process "

That's Oxford. Mirriam-Webster defines it as follows

http://www.merriam-webster.com/dictionary/fire
Quote
Fire - the light and heat and especially the flame produced by burning.

Again we're worrying about semantics when the OP clearly has enough info to understand what he was trying to learn. So why quibble anymore???  It'd be wonderful if he'd jump in and clarify but that rarely happens so I suggest we let this thread die.

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Offline chiralSPO

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Re: Is fire a gas or not?
« Reply #15 on: 10/12/2014 01:22:45 »
I posted the dictionary quotes for you to read.

I respect your knowledge and command physics, but I do think you are wrong on this one. I did read your dictionary definition. However, I don't see why the dictionary definition must be taken as dogma. I looked up photon in the online Merriam-Webster English Dictionary (http://www.merriam-webster.com/dictionary/photon) where it says"

"Full Definition of PHOTON
1:  a unit of intensity of light at the retina equal to the illumination received per square millimeter of a pupillary area from a surface having a brightness of one candle per square meter
2:  a quantum of electromagnetic radiation"

I think the second definition is apt, but I'm not sure how I would argue with someone who claimed that the first was a better definition of photon.
« Last Edit: 10/12/2014 10:28:31 by evan_au »

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Offline chiralSPO

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Re: Is fire a gas or not?
« Reply #16 on: 10/12/2014 01:32:19 »
I wonder if the holographic principle has anything to say about flames. As for string theory how to spin networks fit in this case?

I have wondered that as well. The only other other more abstract way I can think of it is as the orbitals changing and electrons falling down and bouncing up and down and up and down through the energy levels in the space where the reaction is ongoing. Not easy at all to envision, and I'm probably not picturing it quite right, but I think it is a worthwhile thought experiment.

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Offline Bill S

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Re: Is fire a gas or not?
« Reply #17 on: 10/12/2014 17:03:40 »
Quote from: Pete
When he said "Is fire a gas or not?" he......

Mary???

You're right Pete, people should pay close attention to the OP.   [8D]
There never was nothing.

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Offline PmbPhy

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Re: Is fire a gas or not?
« Reply #18 on: 10/12/2014 18:01:04 »
Quote from: Bill S
Mary???
Yes. That's correct.

Quote from: Bill S
You're right Pete, people should pay close attention to the OP.   [8D]
That's absolutely right. All too often people don't pay attention to what the OP wants to learn but instead attempts to interpret what they ask literally rather than addressing what we think that they want to learn. That's the difference between teaching and parroting a dictionary.

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Offline alancalverd

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Re: Is fire a gas or not?
« Reply #19 on: 10/12/2014 18:24:20 »

"Full Definition of PHOTON
1:  a unit of intensity of light at the retina equal to the illumination received per square millimeter of a pupillary area from a surface having a brightness of one candle per square meter
2:  a quantum of electromagnetic radiation"

I think the second definition is apt, but I'm not sure how I would argue with someone who claimed that the first was a better definition of photon.

Neither is the better definition. They are two different things with the same name, like John Smith and John Smith.
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Offline David Cooper

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Re: Is fire a gas or not?
« Reply #20 on: 10/12/2014 19:52:44 »
I think the original question can be interpreted rather more widely than restricting it to a flame. The dispute here is down to the usual thing of people arguing at cross purposes when they all believe in the same things. When you burn a piece of paper with a magnifying glass and produces smoke without flames, the original question still applies: is that fire a gas? Well, no; fire isn't a substance, but is there gas involved as a stage in the process?

Can you have a fire/flame without gas? I'm wondering if you can burn a plasma without there ever being any gas involved, but I suspect that it won't happen because all the bonds between atoms are broken and there can be no chemical reactions. Is that correct?

Someone commented earlier on some flames being a plasma, which leads me to wonder if any flames don't involve a plasma. A tiny candle designed for a birthday cake which plays a certain tune when it's lit depends on there being plasma in the flame to complete a circuit (there being two metal strips in the wick). I've heard that there are some gases which burn with flames of sufficiently low temperature that you can hold your finger in them without injury (and which presumably wouldn't be able to set fire to a piece of paper), but do they involve plasma? A simple way to test would be to see if they can conduct electricity.

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Offline PmbPhy

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Re: Is fire a gas or not?
« Reply #21 on: 10/12/2014 20:43:05 »
Quote from: David Cooper
Someone commented earlier on some flames being a plasma, which leads me to wonder if any flames don't involve a plasma. A tiny candle designed for a birthday cake which plays a certain tune when it's lit depends on there being plasma in the flame to complete a circuit (there being two metal strips in the wick). I've heard that there are some gases which burn with flames of sufficiently low temperature that you can hold your finger in them without injury (and which presumably wouldn't be able to set fire to a piece of paper), but do they involve plasma? A simple way to test would be to see if they can conduct electricity.
A flame is not always a plasma. It has to be hot enough in order to have enough energy to strip electrons from the gas to form ions. See:
http://en.wikipedia.org/wiki/Flame
Quote
Some flames are hot enough to have ionized gaseous components of sufficient density to be considered plasma.

Notice also that it says "A flame (from Latin flamma) is the visible, gaseous part of a fire." This definition is one of the reasons I associated fire with flame.

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Offline evan_au

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Re: Is fire a gas or not?
« Reply #22 on: 11/12/2014 08:42:40 »
I am thinking of a "sparkler" that more adventurous people sometimes use on birthday cakes.
  • This device heats up tiny pieces of metal until they reach ignition temperature, upon which they combine with oxygen in the atmosphere, releasing energy which keeps the metal hot enough to keep reacting with oxygen (until the metal burns away to nothing).
  • Since iron oxide has a melting point of 1566C and a boiling point of 1987C, I am wondering if the reactants get hot enough to form a vapor phase of iron or iron oxide?
  • Or does the thinly divided powder have enough surface area to allow easy access by oxygen, and the extremely exothermic reaction keeps the reactants hot?
  • With a solid wax candle, you have to heat the organic wax to a liquid which can flow up the wick (wax melts around 50C) and then evaporates out of the wick as a vapor (boiling point around 350-400C). This presumably breaks some bonds before the oxygen can react with the wax vapor.
  • I assume the same effects would occur for sparks from an angle grinder? 

So is a spark a fire? And is it a gas?

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Offline jeffreyH

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Re: Is fire a gas or not?
« Reply #23 on: 11/12/2014 10:18:29 »
I am thinking of a "sparkler" that more adventurous people sometimes use on birthday cakes.
  • This device heats up tiny pieces of metal until they reach ignition temperature, upon which they combine with oxygen in the atmosphere, releasing energy which keeps the metal hot enough to keep reacting with oxygen (until the metal burns away to nothing).
  • Since iron oxide has a melting point of 1566C and a boiling point of 1987C, I am wondering if the reactants get hot enough to form a vapor phase of iron or iron oxide?
  • Or does the thinly divided powder have enough surface area to allow easy access by oxygen, and the extremely exothermic reaction keeps the reactants hot?
  • With a solid wax candle, you have to heat the organic wax to a liquid which can flow up the wick (wax melts around 50C) and then evaporates out of the wick as a vapor (boiling point around 350-400C). This presumably breaks some bonds before the oxygen can react with the wax vapor.
  • I assume the same effects would occur for sparks from an angle grinder? 

So is a spark a fire? And is it a gas?

Neither really. I would say it is partly stray electrons and partly ionic molecular components. The flame moves away from a gravitational source but does a spark?
Fixation on the Einstein papers is a good definition of OCD.

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Offline PmbPhy

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Re: Is fire a gas or not?
« Reply #24 on: 11/12/2014 15:23:19 »
Quote from: evan_au
So is a spark a fire? And is it a gas?
No. A spark is a glowing hot piece of matter. If the sparks fall into a white surface then you can look at them after they've cooled down. You'll see that they're small grey/blackish balls of some sort of burned out material. So that part is not a gas but a solid.

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Offline evan_au

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Re: Is fire a gas or not?
« Reply #25 on: 12/12/2014 23:50:06 »
Quote from: jeffreyH
The flame moves away from a gravitational source but does a spark?
A flame rises because the hot gas is less dense than the surrounding cool air, and the "lowest energy state" is with the denser air closer to the center of the Earth.

A spark is a glowing piece of iron or magnesium, which is more dense than cool air, so I expect that a spark will fall in a parabola towards the ground (if it doesn't burn out first).
Quote from: PmbPhy
small grey/blackish balls of some sort of burned out material
  • Candle wax is a hydrocarbon, whose products of combustion are CO2 and water vapor (plus a bit of carbon soot, carried away by convection)
  • Wood has a more complex composition; in addition to the volatile products produced by a candle, it leaves behind a small amount of ash, consisting of non-volatile compounds of Potassium, Sodium, Copper, etc. But it is undoubtedly a "fire".
  • A Sparkler produces a variety of gaseous compounds, but the spark remnants are non-volatile compounds of iron or magnesium. Does the large amount of "ash" disqualify a spark from being a fire? 

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Offline yor_on

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Re: Is fire a gas or not?
« Reply #26 on: 13/12/2014 12:53:06 »
Fire is a result of transformations, interacting. It's also a temperature. Temperatures is also what seems to create 'emergences'. So, can you give me a 'emergence' without a temperature being involved?
=

The point is, I think I can argue at least one, myself.
(Sometimes you find it defined as different 'regimes', cosmologically.)
« Last Edit: 13/12/2014 12:58:45 by yor_on »
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Offline jeffreyH

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Re: Is fire a gas or not?
« Reply #27 on: 13/12/2014 14:35:41 »
Quote from: jeffreyH
The flame moves away from a gravitational source but does a spark?
A flame rises because the hot gas is less dense than the surrounding cool air, and the "lowest energy state" is with the denser air closer to the center of the Earth.

A spark is a glowing piece of iron or magnesium, which is more dense than cool air, so I expect that a spark will fall in a parabola towards the ground (if it doesn't burn out first).
Quote from: PmbPhy
small grey/blackish balls of some sort of burned out material
  • Candle wax is a hydrocarbon, whose products of combustion are CO2 and water vapor (plus a bit of carbon soot, carried away by convection)
  • Wood has a more complex composition; in addition to the volatile products produced by a candle, it leaves behind a small amount of ash, consisting of non-volatile compounds of Potassium, Sodium, Copper, etc. But it is undoubtedly a "fire".
  • A Sparkler produces a variety of gaseous compounds, but the spark remnants are non-volatile compounds of iron or magnesium. Does the large amount of "ash" disqualify a spark from being a fire? 

With a higher energy comes an increase in kinetic energy. If we start a flame in a freefall orbit we get a spherical flame even though there will be a gas in the spacecraft. To simply state this as buoyancy due to density is an oversimplification. Where is the buoyancy/density relationship in freefall? Just to add to this a little. What if we were to ignite a flame inside a sealed container. If we were to apply a force throughout this container such that any gas density variations were evened out would the flame then become spherical or would it still move upwards? This is not a trivial point to make. If it is simply a density relationship with buoyancy being a factor then we will have removed this relationship from the experiment. In which case gravity would be the only factor under consideration.
« Last Edit: 13/12/2014 15:13:43 by jeffreyH »
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Offline Bored chemist

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Re: Is fire a gas or not?
« Reply #28 on: 13/12/2014 21:13:05 »
Fire isn't a substance, it's a process.
Please disregard all previous signatures.

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Offline David Cooper

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Re: Is fire a gas or not?
« Reply #29 on: 13/12/2014 22:45:05 »
When energy is released in our muscle cells, is that the same process as burning? Could it be described as a fire?

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Offline chiralSPO

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Re: Is fire a gas or not?
« Reply #30 on: 13/12/2014 22:51:08 »
I don't think metabolism would count as fire. Fire is typically a self-sustaining, uncontrolled chain reaction (even if the fuel/air ratio is very carefully controlled, there is no control at a molecular level). Metabolism, in muscles or elsewhere, is very tightly regulated cellular process in which enzymes oxidize organic molecules and direct that energy into converting ADP to ATP, or enzymes can convert ATP to ADP and use that energy to do other things.

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Offline evan_au

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Re: Is fire a gas or not?
« Reply #31 on: 14/12/2014 05:56:23 »
Quote from: jeffreyH
If we were to apply a force throughout this container such that any gas density variations were evened out would the flame then become spherical or would it still move upwards?
We could eliminate the effects of gravity on a flame inside a sealed container by dropping the container in a very long vacuum tube.
I expect that the flame would become spherical.

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Offline Bored chemist

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Re: Is fire a gas or not?
« Reply #32 on: 14/12/2014 16:52:32 »
Please disregard all previous signatures.

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Offline yor_on

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Re: Is fire a gas or not?
« Reply #33 on: 19/12/2014 20:25:59 »
I've seen it defined as 'burning' Chiral? Maybe oxidation would be more to the point though?
=

I also have a weak memory of reading of 'two dimensional' fires acting quite strange, looking at the cool link above :). Think they just 'sandwiched' the fire, maybe that too was in a weightless environment?
« Last Edit: 19/12/2014 20:30:00 by yor_on »
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Offline chiralSPO

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Re: Is fire a gas or not?
« Reply #34 on: 03/01/2015 17:57:28 »
I've seen it defined as 'burning' Chiral? Maybe oxidation would be more to the point though?


There are plenty of oxidation (redox) processes that don't involve combustion, burning or fire: batteries, fuel cells, metabolism, browning apples, rusting ships etc.

I am hard pressed to think of a reaction that could qualify as burning without involving redox, but that doesn't mean it's impossible. I can think of a few cases of "explosive polymerization" (involving ethylene oxide or acetylene or similar compounds) which could potentially release enough energy to reach incandescence without involving any redox processes, and also perhaps exothermic decomposition of ozone, but these are special cases...

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Offline evan_au

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Re: Is fire a gas or not?
« Reply #35 on: 04/01/2015 05:37:40 »
Quote from: yor_on
oxidation processes that don't involve combustion, burning or fire: ... rusting ships, etc
Rusting is an oxidation process that occurs very slowly due to Arrhenius' equation: reactions get exponentially faster as temperature rises. If you put steel in a fire, it rusts very quickly.

If you get iron hot enough (eg finely divided steel wool in a Bunsen burner), it burns quite well. With a stronger oxidiser, steel wool burns at room temperature (eg steel wool in fluorine - start video at 2 minutes 45 seconds).

What defines a fire in common usage is that the temperature produced by the reaction is high enough to emit light and heat*. If the temperature is high enough, any hot substance will emit both heat and light through black-body radiation.

To get bulk steel hot enough to sustain a flame in atmospheric oxygen, you have to get it red-hot anyway, by which time it is already emitting light and heat from the external heat source. (Injection of pure oxygen bubbles into molten steel during refining provides much larger surface area than you have with bulk steel.)

So I would say that an oxidation reaction could be called fire if the reaction is self-sustaining, and is exothermic enough to emit heat and visible light much brighter than the surrounding environment.

*Room-temperature bioluminescence in fireflies fits the light-emitting part of the description, but does not conform to our expectation that a fire will also emit lots of heat.
« Last Edit: 04/01/2015 05:40:04 by evan_au »

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Offline lightarrow

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Re: Is fire a gas or not?
« Reply #36 on: 05/01/2015 00:38:35 »
I've seen it defined as 'burning' Chiral? Maybe oxidation would be more to the point though?

I am hard pressed to think of a reaction that could qualify as burning without involving redox, but that doesn't mean it's impossible. I can think of a few cases of "explosive polymerization" (involving ethylene oxide or acetylene or similar compounds) which could potentially release enough energy to reach incandescence without involving any redox processes, and also perhaps exothermic decomposition of ozone, but these are special cases...
Write "aluminium + palladium" in a search engine and choose "video".
When you'll find a video of that intermetallic reaction, you'll be amazed 😊

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Offline chiralSPO

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Re: Is fire a gas or not?
« Reply #37 on: 05/01/2015 15:27:51 »
Yes this reaction is quite impressive. I'm not entirely convinced that the surrounding air didn't contribute to the effect, but the reaction between Pd and Al is apparently exothermic enough on its own, that it probably would have "burnt." This isn't really a redox neutral process, though. Pd is electronegative enough that it could well have oxidized the aluminum (maybe not quite so far as to produce an ionic compound, but the bonding character between aluminum and noble metals is not entirely metallic either--I know gold and aluminum will react to form white or purple compounds that are very poor conductors, which is why Au-Al contacts are typically avoided in circuits.)

Thanks for link!

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Offline lightarrow

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Re: Is fire a gas or not?
« Reply #38 on: 05/01/2015 16:41:48 »
Yes this reaction is quite impressive. I'm not entirely convinced that the surrounding air didn't contribute to the effect,
Here it says no, but who knows... :
http://en.wikipedia.org/wiki/Pyrotechnic_initiator
(see paragraph "Intermetallic", subparagraph "Palladium-aluminium")
Quote
but the reaction between Pd and Al is apparently exothermic enough on its own, that it probably would have "burnt." This isn't really a redox neutral process, though. Pd is electronegative enough that it could well have oxidized the aluminum (maybe not quite so far as to produce an ionic compound, but the bonding character between aluminum and noble metals is not entirely metallic either--I know gold and aluminum will react to form white or purple compounds that are very poor conductors, which is why Au-Al contacts are typically avoided in circuits.)
You are probably right, I didn't know of such compounds between Au and Al; so it's likely that between Pd and Al similar compounds forms.

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