In a thought experiment, a friend proposed to me a machine capable of decomposing any object (e.g., a brick) into its molecules. I'm not a chemist or physicist, but my initial reaction was that this was certainly an environmental issue if used in a larger scale.

Is that right? Or is a molecule so basic that there would be no health concern from such a (theoretical) decomposition.

EDIT @Aesin: My thinking was:

  1. objects can't disappear; the brick will be breathed in, get into water etc.
  2. if we start decomposing more advanced objects, we get all kinds of harmful elements in the air (mercury etc.)
  3. possible radiation from decomposition

As for the purpose: Let's assume it would be used for general waste destruction. Let's assume energy is not a concern (thanks for mentioning it!)

  • $\begingroup$ This question is too broad. Despites this fact, we can assume that if such system exists it will consumes huge amount of energy (1st problem) and will be a source of matter (2nd problem) which will be released in environment. It will be, off course, a matter of concern because it will change working point of a lot of reactions that naturally occurs around us (depending of ẃhat molecule is produced). Anyway, the matter fact is, each time human use and abuse of a technology, drawbacks and issues follows. $\endgroup$ – jlandercy May 4 '14 at 12:59
  • $\begingroup$ Bricks aren't made of molecules. $\endgroup$ – Aesin May 4 '14 at 13:41
  • $\begingroup$ @Aesin mmm I think that for the most part yes, because they are made of clay: silica is a molecule have covalent bonds... $\endgroup$ – G M May 4 '14 at 20:53
  • $\begingroup$ @FrankSeifert: It would help if you could clarify why you think it would be an environmental issue -- you haven't mentioned what you would be expecting it to be used at a large scale to do. $\endgroup$ – Aesin May 4 '14 at 22:01

Molecular level

It depends on the molecules you obtain from the decomposition if you use Plasma gasification on mixed organic-inorganic materials you have syngas ($CO$, $H_2$ ... ) and vitrify matter. Watch this video maybe a little bit misleading but can give you an idea. If you use a complete combustion with organic materials you will have mainly water, carbon dioxide, sulfur dioxide etc., depending on what you are burning. Indeed if you breath sulfur dioxide or nitrogen dioxide is not good for your health, and acid rain are a plague for forests. Incomplete combustion can lead to more hazard for the environment because you can have more complex molecules, sometimes very stable.

objects can't disappear; the brick will be breathed in, get into water etc.

Brick are composed mainly of silicon, not carbon, so you can't use combustion, at a very high temperature you can have silicon, a metal. Maybe some dangerous silane.

if we start decomposing more advanced objects, we get all kinds of harmful elements in the air (mercury etc.)

Mercury is a liquid, not a gas so if you hypothetically discover a cheap technique to get it in the elemental form you will have a liquid.

possible radiation from decomposition

No, you will not have radioactive elements so you don't have radioactivity ( $\gamma$-ray) or other dangerous radiations.

Did you mean particulate?

I think that maybe what you mean if is a danger to powered materials to very tiny particles. Particulate is indeed dangerous but in this case, you don't reach the molecular level. For your brick, this means that you have dust, something quite similar to what you have in your home.

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Decomposing something into 'molecules' is immediately indicative of a non-chemistry background! To try to address your question a bit more directly, I can see a couple of ways of looking at the thought experiment:

1) It decomposes everything to simplest possible component stable molecular structures.

In the case of organic material, plastics etc, you will probably end up with a preponderance of various gases and water, as largely this disassembly is equivalent to complete combustion (CO₂, H₂O, NH₃) likely being the main resulting candidates. These would float out into the atmosphere unless captured.

In the case of inorganic material, e.g. a computer motherboard you will end up with many molecules of various metals, most of which would rapidly oxidise due to their very high surface area (being unimolecular), and various silicates and ceramic unit cells. All of these would be incredibly fine aerosols or dissolved in atmospheric water, similarly rapidly dispersing unless contained.

Results would likely include enhancing the greenhouse effect (on balance as some compounds will diminish it), inducing acid rain (sulfates, nitrates), causing algal blooms/biome damage.

If you had storage for different outputs then you would be producing several industrially useful compounds and if you partnered it with metal reclamation facilities to deal with all the metal oxides it might be a useful way of recycling, energy no object.

2) It decomposes and sorts everything by chemical element.

Assuming you have a nice little storage container for each element (reasonable given you are sorting into the simplest molecule of a pure element), you would end up with various cylinders of oxygen, hydrogen, nitrogen, lumps of metal, lumps/powders of inorganic materials like phosphorus, sulfur, silicon. This would be potentially useful, but incredibly energetically expensive even beyond the separation system outlined by Uncle Al, so would be considerable only in the case of having essentially limitless free energy (many nuclear fusion plants/orbital solar collectors/dyson sphere type energy availability I suspect).

Issues here would relate to various elements being highly reactive on contact with air (or rather the oxygen/water in it). Obvious examples include allotropes of phosphorus and the rare earth metals.

Other issues unaddressed include fractional distillation and cracking of small molecule gases into smallest molecule gases, how to prevent reaction inside the vessel i.e. actually separate things rather than just provide them with huge amounts of energy to react with each other etc

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