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#1
I start weird conversations; this was one of them.

The existance of something is measured by it's mass. As such, anything lacking mass is not recognised as existing. Even air has molecules which have infintisimal weight to them. However, given that fire is a chemical reaction which consumes in order to exist, what does fire weigh?

Does it weigh anything at all? If so, how much?

Please help.
#2
since fire is the emission of energy (light and heat) due to particles splitting, fire itself has as much mass as the energy being released during the oxidation, which isn't measurable in normal circumstances.
Last edited by CoreysMonster at Jun 10, 2010,
#4
Haha I was about to say that fire is energy too. Uh well since E=mc^2 then it does have mass but I suppose you can't measure it unless you measure an object before it's burned then after and you also need to think about the smoke that is released because the carbon has mass too.

so then E(fire) is = to (Minitial - Mfinal) / 300000mps

maybe?
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Last edited by Imperial at Jun 10, 2010,
#5
fire is just a kind of chemical reaction...the flames u see are the result of the visible light energy given off by the reaction so fire doesnt have a mass much in the same way freezing doesnt have a mass.

someone will most likely argue with me but thats how i understand it
#6
mass of what was burnt*acceleration due to gravity = weight of the fire?
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#7
Interesting question. Fire is not a material thing, it's just a release of energy triggered by chemical reactions, so it doesn't weigh. It's like asking if "burning" weigh, or "playing guitar" weigh. These are just actions.
#8
So, if it was burning something, would it add weight to it, or would the consumption rate result in a much faster decay rate?

Quote by Orethor
fire is just a kind of chemical reaction...the flames u see are the result of the visible light energy given off by the reaction so fire doesnt have a mass much in the same way freezing doesnt have a mass.

someone will most likely argue with me but thats how i understand it


So solid water will weigh exactly the same as liquid water?
Last edited by Colohue at Jun 10, 2010,
#9
Fire is just heat and light resulting from a chemical reaction, as others have pointed out, Einstein's equation can be used to determine the mass.
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#10
Quote by Colohue
So, if it was burning something, would it add weight to it, or would the consumption rate result in a much faster decay rate?

hm, an interesting question.

To set something on fire, you need to add energy, so in a way, you ARE adding more weight to it, but as the chemical process continues, you end up with less mass than when you started, because the energy released during burning is more than the initial "jump start", so to speak.
#12
would the weight of the fuel used 2 light said fire also be taken into consideration ? failing that, just talk about sex instead - much more interesting topic
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#13
i only used the freezing example to try and explain that fire isnt a "thing" its the energy given off by combustion

but yes the water weights the same as ice as a liquid but its volume changes
#14
Quote by Icarus Lives
I thought fire is just an illusion caused by intense heat. Like heat waves. Its just moving air.

No, it's not.

Fire is light being ommitted from molecules falling apart due to the high amount of energy they have, it's a physical process, not an illusion.
#15
Quote by CoreysMonster
since fire is the emission of energy (light and heat) due to particles splitting, fire itself has as much mass as the energy being released during the oxidation, which isn't measurable in normal circumstances.


Exactly. Fire does not have mass as it is just basically thermal energy. It'd be like asking if light weighs anything. Since it is energy, not matter, it has no measurable mass. It's products and reactants, however, do have mass.
Last edited by D&DLover at Jun 10, 2010,
#16
Quote by CoreysMonster
hm, an interesting question.

To set something on fire, you need to add energy, so in a way, you ARE adding more weight to it, but as the chemical process continues, you end up with less mass than when you started, because the energy released during burning is more than the initial "jump start", so to speak.



energy doesnt have mass, mass can have energy ie kinetic/potencial but energy doesnt have mass....
#17
Quote by KingHenrik1967
would the weight of the fuel used 2 light said fire also be taken into consideration ? failing that, just talk about sex instead - much more interesting topic


I very much disagree.

Sure, the weight of the fuel is valid. However, this makes it much harder to work out the actual weight of the fire since, in uncalculatably short an amount of time, the mass of the fuel and air is already changing.

That said, addition question: Does the air that burns in this chemical equation add to the weight of the fire, and thus the object burning, even momentarily?
#19
Quote by Colohue
So solid water will weigh exactly the same as liquid water?

I think that it would. The number of molecules is exactly the same, they are just arranged differently.
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#20
Quote by Orethor
energy doesnt have mass, mass can have energy ie kinetic/potencial but energy doesnt have mass....

Energy and mass are equivalent according to Einstein, so energy has a mass, it's been measured and proven.

Rockets flying at high speeds gain mass.
#21
Quote by Colohue

So solid water will weigh exactly the same as liquid water?

Yes.
#22
Quote by SRX700
I think that it would. The number of molecules is exactly the same, they are just arranged differently.

Pretty much this. If you freeze a liter of water (weighs a kilogram) it will become a kilogram of ice. However, the volume of the ice will be bigger and the density smaller. IIRC, water has maximum density at about 4 degrees celsius, being the only(?) exception as other substances just get denser the colder they are.

What I think about the fire thing (I've also thought about what fire really is): I think the fire itself doesn't weigh, it's energy. The flames you see are gas molecules that just are so hot that they are colored.
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#23
Quote by CoreysMonster
Energy and mass are equivalent according to Einstein, so energy has a mass, it's been measured and proven.

Rockets flying at high speeds gain mass.

But weight =/= mass.
So fire in 0g(or at least as close as you can get) will have a weight so small as to be immeasurable.
#24
Ok, here goes!

First we have to think of what fire is. Fire is simply the chemical reaction of something with oxygen. Lets take the case of wood. Wood contains lots of Carbon, which, if given enough energy (such as a spark of electricity or excessive heat) will react with the oxygen in the air. As the carbon is being separated, it gives off energy which was previously holding the carbin atoms together (it's binding energy). The carbon atom now pairs with the Oxygen (02) molecules, creating Carbon Dioxide (CO2). All excess energy is given off as heat.
The binding method in the case of carbon is a covalent bonding. This is where two atoms 'share' an electron, completeing their outer shell. The energy released from one binding can cause another to split, and so on creating a chain reaction- hence why fire spreads.

So what do we actually see?
When the carbon atoms attach to the oxygen molecules, they do so in an 'excited' state. As the molecules fall down to their ground level state, they release a photon of light, whose wavelength (and therefore colour) depends on the size of the gap in energies it is falling through. For carbon dioxide, this turns out to be yellow/orange light.

So to sum it all up, fire is just light and heat. Therefore the mass of the fire is the sum of the mass of heat and light. However, since light is massless (although it can have an 'apparent mass') this leaves just the mass of heat.

So finally, the mass of heat is just simply the mass of air inside the fire, which us mainly carbon dioxide. This comes out on average as 44g per 6x10^23 molecules and therefore is extremely small.

Edit: for the whole thing about mass and energy, Einstein stated that mass is just one form of energy, energy doesn't actually have a mass, but an amount of energy COULD BECOME a mass. That is what is meant by E=mc^2.
Last edited by l3vity at Jun 10, 2010,
#25
Quote by MightyAl
But weight =/= mass.
So fire in 0g(or at least as close as you can get) will have a weight so small as to be immeasurable.

fire on earth has a weight so small it's immeasurable.
#26
Quote by CoreysMonster
fire on earth has a weight so small it's immeasurable.

But not on the surface of the sun!
#27
Quote by CoreysMonster
hm, an interesting question.

To set something on fire, you need to add energy, so in a way, you ARE adding more weight to it, but as the chemical process continues, you end up with less mass than when you started, because the energy released during burning is more than the initial "jump start", so to speak.

I could be wrong here but does burning something not add mass? It seems counter-intuitive I know but the example they showed us at school was a bit of bread, when it got burned to a crisp in a toaster it weighed more because it became oxidised, so it gained oxygen atoms rather than losing bread molecules
#28
Quote by l3vity
*some real knowledge about this*

I think I can safely say after this:

/thread
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#29
Quote by nigeltheginger
I could be wrong here but does burning something not add mass? It seems counter-intuitive I know but the example they showed us at school was a bit of bread, when it got burned to a crisp in a toaster it weighed more because it became oxidised, so it gained oxygen atoms rather than losing bread molecules

You're thinking about the fuel and the residue, not the actual fire.
#30
Quote by MightyAl
You're thinking about the fuel and the residue, not the actual fire.

I know but I don't really understand this concept so i was picking at semantics in an effort to make myself seem more intelligent
#31
Quote by nigeltheginger
I could be wrong here but does burning something not add mass? It seems counter-intuitive I know but the example they showed us at school was a bit of bread, when it got burned to a crisp in a toaster it weighed more because it became oxidised, so it gained oxygen atoms rather than losing bread molecules


Yes, that is the case with that scenario. If you collected all of the products, they will weigh more than just the initial bread. However, if you take into account all of the reactants, the weight before and after should be equal. It doesn't really have anything to do with the fire argument, though.
#32
Quote by nigeltheginger
I know but I don't really understand this concept so i was picking at semantics in an effort to make myself seem more intelligent

That's what the internet is for.
#33
ok- after a bit of maths im not going to bore you with, and using wikipedia for the average heat of a candle, and assuming normal atmospheric pressure and a volume of flame approximately 1cm^2, i have calculated the mass of the fire to be 0.029g -so quite small
#34
Quote by l3vity
ok- after a bit of maths im not going to bore you with, and using wikipedia for the average heat of a candle, and assuming normal atmospheric pressure and a volume of flame approximately 1cm^2, i have calculated the mass of the fire to be 0.029g -so quite small


Which includes the air molecules, right? Not just the photons given off?
#35
Quote by l3vity

So to sum it all up, fire is just light and heat. Therefore the mass of the fire is the sum of the mass of heat and light. However, since light is massless (although it can have an 'apparent mass') this leaves just the mass of heat.

So finally, the mass of heat is just simply the mass of air inside the fire, which us mainly carbon dioxide. This comes out on average as 44g per 6x10^23 molecules and therefore is extremely small.

Edit: for the whole thing about mass and energy, Einstein stated that mass is just one form of energy, energy doesn't actually have a mass, but an amount of energy COULD BECOME a mass. That is what is meant by E=mc^2.


However, accepting that you're right about the mass of heat being the mass of air inside the fire, doesn't this make the weight inconsistent due to the constant income and expenditure of air? Also, does this change when burning different fuels do to their respective densities?

Quote by l3vity
ok- after a bit of maths im not going to bore you with, and using wikipedia for the average heat of a candle, and assuming normal atmospheric pressure and a volume of flame approximately 1cm^2, i have calculated the mass of the fire to be 0.029g -so quite small


What fire? An average candle? This is not really an answer, since it's not about the fire, but rather based on the burning of a solitary item.
Last edited by Colohue at Jun 10, 2010,
#36
Quote by Colohue
The existance of something is measured by it's mass. As such, anything lacking mass is not recognised as existing. Even air has molecules which have infintisimal weight to them. However, given that fire is a chemical reaction which consumes in order to exist, what does fire weigh?

False.
#37
Quote by Colohue
However, accepting that you're right about the mass of heat being the mass of air inside the fire, doesn't this make the weight inconsistent due to the constant income and expenditure of air? Also, does this change when burning different fuels do to their respective densities?



I think what he's trying to say that the mass of the flame is the same as the gas in it, which in usually is CO2. The flames mass probably changes though because more CO2 is released constantly and some if it is cooled and will appear as smoke. Basically, it's REALLY light as fire usually "goes" up meaning it's lighter than the air around it.
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#38
Quote by Colohue
So solid water will weigh exactly the same as liquid water?
Yes, if you take into consideration that water gains volume when frozen. So, if you take a liter of water and freeze it, it will have the same weight in liquid and solid states. The solid water will occupy a larger volume, though. So say you consider two identical volumes of water, one liquid and one solid; in that case, the liquid water will weigh more.
#39
Quote by Colohue
However, accepting that you're right about the mass of heat being the mass of air inside the fire, doesn't this make the weight inconsistent due to the constant income and expenditure of air? Also, does this change when burning different fuels do to their respective densities?


What fire? An average candle? This is not really an answer, since it's not about the fire, but rather based on the burning of a solitary item.



of course, you cannot measure the EXACT mass of a fire, as you are correct in saying particles come and leave the fire, but on average it would be roughly constant given that the fire was neither growing or dying out.
Because different fuels are made up of different things, they require different amounts of energy for them to be sperated and attach to oxygen, which is why some materials burn at a lot hotter temperatures than others, a candle is aprroximately 1000c where a ciggarette is only about 400.

And yeah, i used a candle as an example and made some assumptions, such as to the size of the falme and also that we can see the entirety of the fire (also not true). I chose a candle as the flame is quite small, and it had the average temperature for one on wikipedia
#40
Does this mean that fire could be a tool used for measuring the elemental properties of air then, since different places have different levels of Oxygen, Nitrogen, Carbon Dioxide, Argon etc.?
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