Can a pencil be put back together

[Zygotic Embryo]

A friend of mine was asking the teacher, why can't a pencil ( or any object for that matter) just simply..be put together if it's snapped in half. Are bonds broken, what's going on here? What's causing me from connecting the two pieces back together back to its original form without a catalyst such a glue... This question is on the atomic or subatomic level, peers where saying " because the wood and graphite is separated" that's true in a sence, but i want to go atomic.

 

[Cyrus]

Im no chemist, but there is probably an energy barrier that must be overcome before the bonds will re-establish themselves. In order to get over this energy barrier, you will need to supply some sort of energy input to do this. If this were not true, then you would be able to put broken pencils back together again and see a net amount of energy released as the bonds are made. Remember, chemical bonds are either exothermic or endothermic. You can't simply just "make bonds" without taking energy into consideration.

 

[Zygotic Embryo]

But this is no chemical change it's a physical change correct?

 

[DaveC426913]

One of the things that happens, though by no means the only factor, is that any "loose ends" will immediately be surrounded by oxygen and begin oxydizing. Same with hydorgen. AQlmost instantly, the edges are not volatile.

Then again, this would suggest that, in a vacuum we wouldn't have that problem...

 

[Cyrus]

But this is no chemical change it's a physical change correct?

Incorrect, you must re-make chemical bonds with the pencils carbon and graphite atoms for it to become 'unbroken'

Edit: It has been a while since I took Chemistry. In a sense, yes it is physical because the chemical properties of the pencil are the same.

 

[LeonhardEuler]

One of the things that happens, though by no means the only factor, is that any "loose ends" will immediately be surrounded by oxygen and begin oxydizing. Same with hydorgen. AQlmost instantly, the edges are not volatile.

Then again, this would suggest that, in a vacuum we wouldn't have that problem...

It would also suggest that inert materials like platinum or materials that are already oxides such as SiO2, would not have this problem. (But like you said there could be other factors as well) I once asked this question and someone told me that the air physically obstructs the re-formation of the bonds. Again this would suggest that in a vacuum, you could simply stick solids back together. I don't know if this is true.

 

[Zygotic Embryo]

Oh, i was talking about the seperating, of the carbon and graphite atoms.

And dave, why doesn't the pencil in whole.. just oxidize it's? I understand what your saying, by seperating the pencil.. the " loose ends" will oxydize.

 

[Cyrus]

What do you mean,

Oh, i was talking about the seperating, of the carbon and graphite atoms.

?

I just explained why.

 

[Zygotic Embryo]

Theoretically, in a vacuum it's possible..

but if air obstructs the reformation of bonds, wouldn't it also obstruct the formation of bonds? The pencil doesn't occur naturally.. is that were you going? Are you saying, the bonds are separate for " the wood" and the "graphite". And there just combined by pressure to make the pencil, and when the pencil is broken, it can't be put together because of the separate bonds?

I thought it delt with antimatter and matter ordinances.. but I am probably wrong.

 

[LeonhardEuler]

Oh, i was talking about the seperating, of the carbon and graphite atoms.

Yes, but it seems likely that the same mechanism is responsible for preventing all solids from sticking together, rather than millions of different mechanisms for different solids that all have the same effect.

 

[Cyrus]

Am I speaking Chinese?

 

[LeonhardEuler]

Theoretically, in a vacuum it's possible..

but if air obstructs the reformation of bonds, wouldn't it also obstruct the formation of bonds? The pencil doesn't occur naturally.. is that were you going? Are you saying, the bonds are separate for " the wood" and the "graphite". And there just combined by pressure to make the pencil, and when the pencil is broken, it can't be put together because of the separate bonds?

Yeah, I don't think there is any chemical bond between the wood and graphite in a pencil, but I'm not saying the air thing is correct, I'm just saying that's how someone explained it to me, but it never sat well with me.

 

[Cyrus]

Yeah, I don't think there is any chemical bond between the wood and graphite in a pencil, but I'm not saying the air thing is correct, I'm just saying that's how someone explained it to me, but it never sat well with me.

This is a science forum. Leave the crackpotery out of it, please.

 

[Zygotic Embryo]

I understand you have to "remake the bonds"

but what are the bonds?

You answer my question, I am just lookin for a more in depth answer

is it the " equilibrium" concept?

 

[LeonhardEuler]

This is a science forum. Leave the crackpotery out of it, please.

What do you mean?

 

[Cyrus]

The bond's are whatever holds the atoms together, Colvalent or Ionic or Vander-walls.

What do you mean nothing is lost but the "miniscule loose edges?" Where are you getting this bad science from?

 

[Zygotic Embryo]

LoL.
It is a physical change right? I understand how it could be a chemical but it seems its more of a physical change..
It's obvious bonds are broken. I am asking what the bonds are, is it colvalent, ionic or vander-walls.
WHY Can't the BONDS just simply, go back together? The pencil still has it's properties, it's just seprated.

Im in ap chemistry in high school, your level of understanding is probably above mine, but my teacher couldn't answer this.

 

[Cyrus]

WHY Can't the BONDS just simply, go back together?

I thought I already said that to put bonds back together requires an input of energy in this case.

I appologize about misunderstanding you when you said physical change. By your definition, it is a physical change because you are not changing the chemical composition of the pencil graphite.

 

[Zygotic Embryo]

Ok thanks, that answer's my question.

Now could this be any type of energy?

 

[Zygotic Embryo]

* Double post.

 

[Rach3]

This is a biology question. Pencil is wood; wood is tree; tree is plant. I know nothing about plants, so let's see what wikipedia has to say:

The primary cell wall, built by the plant first, is composed of cellulose microfibrils aligned at all angles. Microfibrils are held together by hydrogen bonds to provide a high tensile strength. Cell walls of neighbouring cells are held together by a shared gelatinous membrane called the middle lamella, which contains magnesium and calcium pectates (salts of pectic acid).Cells interact though plasmodesma(ta), which are inter-connecting channels of cytoplasm that connect to the protoplasts of adjacent cells across the cell wall.

http://en.wikipedia.org/wiki/Cell_wall

Maybe a biologist will enlighten this? Seems H-bonding between cellulose provides struture at the cellular level, and some sort of memberane connects those things together. Whatever it is, it's obviously some sort of intramolecular force between large molecules.

 

[Lyuokdea]

Creating any chemical bond requires energy greater than the activation energy. Think of it like this: At some point in order to make a chemical bond, two atoms must move close to each other, then the electrons can fill orbitals evenly and are in a lower energy state. But if two separate atoms are far apart and move together, they have to first get close, at that point, the electron shells of both atoms will repel each other because they are like charges and like charges repell. Thus there must be sufficient energy in the system for the two separate atoms to overcome this electronic repulsion and bond together.

~Lyuokdea

 

[Zygotic Embryo]

thanks, ill read up on that now

 

[LeonhardEuler]

I thought I already said that to put bonds back together requires an input of energy in this case.

That still begs the question, though, doesn't it? What you are suggesting is that there is some kind of gigantic potential energy barrier to overcome. What is the source of this? It is apparent that it would require a large input of energy to put two solids back together, but the question is, why?

By the way, I'm still curious to know what you meant by:

This is a science forum. Leave the crackpotery out of it, please.

 

[Lyuokdea]

The question involves very little biology. Because wood is an organic compound, the exact structure of its bonding is dependent on biological mechanisms, and when the pencil is broken, the energy required to put it back together depends on what molecules make up the fractured regions, however, the method is the same. It is just chemicals overcoming activation energy in order to bond, and while the numbers will be different for different compounds, the process is the same for both organic and inorganic compounds.

~Lyuokdea

 

[LeonhardEuler]

Creating any chemical bond requires energy greater than the activation energy. Think of it like this: At some point in order to make a chemical bond, two atoms must move close to each other, then the electrons can fill orbitals evenly and are in a lower energy state. But if two separate atoms are far apart and move together, they have to first get close, at that point, the electron shells of both atoms will repel each other because they are like charges and like charges repell. Thus there must be sufficient energy in the system for the two separate atoms to overcome this electronic repulsion and bond together.

~Lyuokdea

I still wonder why, for instance, you can easily recombine liquid metals, but not solid ones. It does seem to be possible to stick two peices of ice together, though. I wonder if this is due to a different nature of the bonding, or simply the ice melting and re-freezing.

 

[Zygotic Embryo]

It is just chemicals overcoming activation energy in order to bond, and while the numbers will be different for different compounds, the process is the same for both organic and inorganic compounds- Lyuo

Now were talking.

So in order to put the pencil back, i would have to create a chemical energy, that pertains to the pencil's molecules, THAT is greater then the activation energy. Which, is impossible outside of a vacuum? Right

 

[Lyuokdea]

For liquid metals you don't have the same intermolecular forces that you have for solid metals. When you break a pencil it is the repulsion in intermolecular forces that you have to overcome. For a single liquid metal, or a liquid of any type in fact, those forces don't exist. However, for two liquids you can definitely get differences in composition due to bonding structure (think oil and water)

For ice, I remember talking to a Pchem professor about this, it is due to the fact that there is no such thing as solid ice at the border region. In fact, the very idea of solid is ill defined on the border, as, a solid is due to a rigid, regular bond structure which does not exist at the border in many materials. The boundary of ice is always liquid at all temperatures, and is some blend of liquid and solid at extremely cold temperatures. Thus, when pressed together, the two liquids want to go to a lower energy state by turning solid, and thus they solidify together and Hydrogen bonding holds the entire block of ice together.

~Lyuokdea

 

[Lyuokdea]

It doesn't need to be in the form of a chemical energy, it could be in form of many sorts of forces. For instance, it is certainly possible that, even in air, you could force the pencil back together by simply pushing "hard enough" Such that the force you exerted on both sides of the pencil is greater than the repulsion force that is keeping the pencil apart.

This is of course, practically impossible for several reasons. The type of force required would certainly shatter other parts of the pencil long before it creates enough force to meld the pencil parts together, also, it is unlikely you can line the pencil up well enough for the pencil to look "good as new" Furthermore, some atoms at the border of the fracture probably came off in their own pieces separate from the two main ones, flying off as dust for instance, which will leave gaps in any reformed pencil.

~Lyuokdea

 

[LeonhardEuler]

For liquid metals you don't have the same intermolecular forces that you have for solid metals. When you break a pencil it is the repulsion in intermolecular forces that you have to overcome. For a single liquid metal, or a liquid of any type in fact, those forces don't exist. However, for two liquids you can definitely get differences in composition due to bonding structure (think oil and water)

~Lyuokdea

Do you know why there are not significant repulsive intermolecular forces in liquid metals, but there are in solids?