weight after burning

[Rhythmdvl]

Wasn’t there a documentary on this? Narrated by B. Pitt or G. Clooney, I think. Burn after Weighing or something like that.

[Duke]

@Bill_Door

I’ve heard that quote, “90% of a tree is air”, but did you ever try to hit a golf ball through one? Every stinkin’ time I hit the part made out of wood. Statistically improbable, but true.

Golfers who say “90% of a tree is air” usually aren’t great golfers. They’re also the ones often seen trying to scramble out from under trees.

[Bozuit]

@kayaker

So. . .wait. . .you’re saying matter cannot be created or destroyed?:eek:

Who said that?

@Rhythmdvl

Wasn’t there a documentary on this? Narrated by B. Pitt or G. Clooney, I think. Burn after Weighing or something like that.

Yeah that was a pretty good one, even if Mr Pitt had to take a bullet in the head as the price for his investigations.

[Exapno_Mapcase]

The answer to the OP’s question comes with major historical significance. It was by answering this question that the phlogiston theory was finally overturned.

A nice concise version is given in Much Ado about (Practically) Nothing: A History of the Noble Gases, by David Fisher.

If something had phlogiston in its essence, it burnt; if not, it didn’t. The theory explained why something like wood could burn for a while, but then go out: when it had used up all its phlogiston, it was no longer burnable. It also explained why the burnt wood weighed less than the original: the loss in weight was phlogiston which had been used up. Finally, it explained why a burnable substance enclosed with a fixed amount of air would stop burning sooner than if it were in the open air: when the enclosed air had taken up its fill of phlogiston, it couldn’t accept any more, even though the wood had plenty to spare, and so no more could be emitted and the wood stopped burning.

An excellent theory, explaining all the observable facts. But then those damned natural philosophers did one experiment too many (a fault many of us still share): they burst the metal magnesium, and found that it actually *gained *weight! Others began collecting all the soot and ashes that blew away in the smoke of a wood fire, and when they put this all together they found that not only hadn’t the wood lost any weight at all, it too had gained weight.

[Enilno]

@Bozuit

No mass is converted to energy by combustion.

Isn’t this kind of fuzzy since mass and energy are equivalent? In any case, the energy released during combustion comes from the energyin the molecular bonds, which does have mass.

[Bill_Door]

@Duke

Golfers who say “90% of a tree is air” usually aren’t great golfers. They’re also the ones often seen trying to scramble out from under trees.

Sure, but I can tell the age and species of a tree just by hearing a golf ball bounce off it. That’s gotta be worth something.

[Duke]

@Bill_Door

Sure, but I can tell the age and species of a tree just by hearing a golf ball bounce off it. That’s gotta be worth something.

Golf shot #1: The Larch.

[Bill_Door]

@Mangetout

OK. Not sure I quite agree with those numbers though. Dry Scots Pine (not even a very dense wood) is about 0.5g/cm[sup]3[/sup], diamond is about 3.5g/cm[sup]3[/sup]. Balsa might be 90% air, but it seems as though few other woods will be 90% air, and hardly any living trees will.

Yeah, but of the total volume of a tree very little of it is wood. It’s mainly spaces between the branches. Just like a house. It may occupy a volume of 30,000 cubic feet, 30’X50’X20’, but it’s mostly the empty spaces between the walls.

[Bozuit]

@Enilno

Isn’t this kind of fuzzy since mass and energy are equivalent? In any case, the energy released during combustion comes from the energyin the molecular bonds, which does have mass.

You may be right about the bonds. Wikipedia tells me “A common hardwood, red oak, has an energy content of 14.89 megajoules per kilogram” (I know it’s not paper). Converting this to mass for 5 pounds (using the good old-fashioned E = mc²) gives 0.000000376g as the mass of all that energy. So, at least for the purposes of OP’s question, energy is pretty irrelevant even if technically it is a factor.

Disclaimer: I’m too lazy to double check my calculations so they may be way off.

[Dufus]

My upwind neighbor burns about 3 cords (12,000 pounds) of wood in the winter. He probably has 200 pounds of ashes to deal with. Being on the downwind side, I get the 11,800 pounds of smoke to deal with.

[Machine_Elf]

@Bozuit

No mass is converted to energy by combustion.

This is not true. In a combustion reaction, the products weigh more than the reactants. The mass difference is tiny but non-zero, and equates to the energy released in the reaction as E=mC[sup]2[/sup].

[thelabdude]

@Exapno_Mapcase

Others began collecting all the soot and ashes that blew away in the smoke of a wood fire, and when they put this all together they found that not only hadn’t the wood lost any weight at all, it too had gained weight.

With all the loss of CO2 and H2O, I find that unlikely unless you collect the gases too.

Note, while it may be harder to hit a golf ball through a tree than it looks, some of the tree is made out of water and minerals from the ground, not CO2 from the air.

@Malacandra

Roughly speaking, cellulose is polymerised C[sub]6[/sub]H[sub]12[/sub]O[sub]6[/sub] and I think it’s been established * that when sugar burns the oxygen from it ends up in the carbon dioxide, not the water, so engineer_comp_geek would still be right on that point.

• (You can use heavy oxygen, oxygen-18, in the glucose molecule - or burn it in heavy oxygen instead - and see where the heavy oxygen ends up.)

I think I will accept that without cite. Do you have figures on whether the oxygen in the cellulose came from the CO2 or water?

[Bozuit]

@Machine_Elf

This is not true. In a combustion reaction, the products weigh more than the reactants. The mass difference is tiny but non-zero, and equates to the energy released in the reaction as E=mC[sup]2[/sup].

I take it you didn’t read my last post.

[Mangetout]

@Bill_Door

Yeah, but of the total volume of a tree very little of it is wood. It’s mainly spaces between the branches. Just like a house. It may occupy a volume of 30,000 cubic feet, 30’X50’X20’, but it’s mostly the empty spaces between the walls.

:smack: gotcha.

[lisiate]

@Exapno_Mapcase

The answer to the OP’s question comes with major historical significance. It was by answering this question that the phlogiston theory was finally overturned.

A nice concise version is given in Much Ado about (Practically) Nothing: A History of the Noble Gases, by David Fisher.

Indeed, Antoine Lavoisier’swork on pretty much this question marks the beginning of modern chemistry.

[njtt]

@Exapno_Mapcase

The answer to the OP’s question comes with major historical significance. It was by answering this question that the phlogiston theory was finally overturned.

It makes a nice parable about the triumph of the scientific method over ancient superstition (or something), but the fact is that the phlogiston theory had not been around in any recognizable form for much more than a century (from c.1667) before Lavoisier refuted it, and was never particularly ubiquitous.

Furthermore, this bit

An excellent theory, explaining all the observable facts. But then those damned natural philosophers did one experiment too many (a fault many of us still share) . . . Others began collecting all the soot and ashes that blew away in the smoke of a wood fire, and when they put this all together they found that not only hadn’t the wood lost any weight at all, it too had gained weight.

is just plain wrong. As pointed out in the first few posts of this thread, most of the mass is carried away as gases. The soot and ashes will weigh a lot less than the original wood or paper.

[copperwindow]

@engineer_comp_geek

When you burn paper, you take all of the materials that the paper is made out of (mostly processed cellulose which is a combination of carbon, hydrogen, and oxygen compounds) and combine them with oxygen in the air.

Well then, what is the ash made out of? Why didn’t all of the paper get converted to CO2?

[Boozahol_Squid_P.I]

@lisiate

Indeed, Antoine Lavoisier’swork on pretty much this question marks the beginning of modern chemistry.

I think you mean modern chemiftry.

[Michael63129]

@copperwindow

Well then, what is the ash made out of? Why didn’t all of the paper get converted to CO2?

Ash is made up of minerals like potassium (in fact, the name potassium comes from potash, which comes from wood ashes) and all of the other trace minerals needed for cellular functions, which don’t form gaseous combustion byproducts.

ETA: Here is what Wikipedia says about ash composition:

Wood ash contains calcium carbonate as its major component, representing 25[4] or even 45 percent[5] Less than 10 percent is potash, and less than 1 percent phosphate; there are trace elements of iron, manganese, zinc, copper and some heavy metals.[4] However these numbers vary as combustion temperature is an important variable in determining wood ash composition.[1] All of these are, primarily, in the form of oxides.

[Exapno_Mapcase]

@njtt

It makes a nice parable about the triumph of the scientific method over ancient superstition (or something), but the fact is that the phlogiston theory had not been around in any recognizable form for much more than a century (from c.1667) before Lavoisier refuted it, and was never particularly ubiquitous.

Wait, phlogiston had been around for only 100 years so that diminishes its importance? Priestly and other top chemists in England, Germany, and France, the only countries that influenced science in the day, weren’t advocating it? Lavoisier’s refutation of their specific work was something of no importance that even so makes him the father of modern chemistry?

I hate arguments about who is to be credited for what. But dismissing the phlogiston theory entirely seems a bit much.

Furthermore, this bit

is just plain wrong. As pointed out in the first few posts of this thread, most of the mass is carried away as gases. The soot and ashes will weigh a lot less than the original wood or paper.

It’s a paragraph of introduction to a more detailed section that I have no desire to transcribe and see no need to, either. I can’t imagine that you or anyone read it as a complete explanation. I will note that the author, a professor emeritus of chemistry, considers phlogiston theory somewhat more important than you do.