Tag proposal: [decomposition]

Question

Making my way through old reaction questions, I constantly wish that something regarding decomposition existed. It's not acid-base, it's not stoichiometry, and it definitely isn't reaction-mechanism. Sometimes it's hard to find ancillary tags when the main focus of the question is regarding the act of decomposition.

To be honest, I wish there was a single tag for each of the general reaction classes. For the sake of discussion, this is the one I'd want the most.

• Counterargument: it will just serve as a dumping ground for old reaction questions.

• Another counterargument: Tag for dissolution process? gives solubility. This is not really correct here, since the focus isn't usually around some precipitate, it's more general.

Potential candidates:

• What does teflon give on decomposition?
• What exactly happened when I added KOH to hydrogen peroxide?
• Products of Lead(II) nitrate decomposition
• What metals aren't dissolved in/attacked by aqua regia?
• Thermal decomposition of calcium propionate
• Decomposition products of hexaurea-chromic-chloride-trihydrate

In these cases, I'm not making the argument that these are good questions, but that the present tags are poor because they are incomplete.

Here is it less of an issue, because the focus isn't on the decomposition itself:

• Calculating energy change for calcium carbonate decomposition

Answer 1

I did initially have certain reservations about this tag. The best way I can phrase it is that decomposition isn't traditionally a concept or subfield in chemistry. In that sense, I mean that textbooks don't contain chapters specifically on decomposition reactions (do they?), and there aren't specialised books on decomposition (2-second Google search doesn't reveal any). A quick glance through our current tag list shows that most of our current tags don't have this problem. So its usefulness in helping people filter questions they like/don't like is probably not as good as other tags. See, for example, Q2 and Q9 on MAR's tag test.

Overall, though, I'd probably still be in favour of creating it. Reasons:

1. Especially given that we already have combustion, synthesis, acid-base, and redox, making a new tag decomposition does seem like a logical step to take.

   Most decomposition reactions can be described as internal redox. For example, the decomposition of hydrogen peroxide is a disproportionation, so technically redox would be applicable. However, simply lumping redox on them sort of misses the point IMO. e.g. the Teflon question is probably redox, but it makes little sense to describe it as such.

2. As you said, it's not good when we have questions that don't have any appropriate tags.

3. Its scope is well-defined: IUPAC Gold Book

4. Regarding your counterarguments: since decomposition is a more specific tag than reaction, so I don't see it becoming the same kind of indiscriminate dumping ground with 900+ questions. On top of that it doesn't suffer from the newbie "idk what tag to put, let's put reaction" issue. So in these respects it certainly outdoes its predecessor.

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P/S I am not a fan of displacement, though. As people learn more chemistry, they start to realise that there are more descriptive and specific terms to classify reactions: in this case, either acid-base, redox, or precipitation.

Answer 2

One possible problem with decomposition is that there's potentially a subjective element to its definition. In one situation a reaction might be a decomposition, while in another it's a desired transformation. I don't have the organic chops to come up with a really punchy example, but take ester hydrolysis as representative:

• If one wants to work with a particular ester, say ethyl chloroacetate, but the conditions one needs for other reasons favor hydrolysis to ethanol and chloroacetic acid, then I'd say the ester is decomposing in that milieu.

• If one specifically desires an ester to hydrolyse, though, e.g. when one is using it (if one ever would...) as a protecting group, then that hydrolysis is not decomposition but a specific reaction of interest.

So, in the end, I'm of divided opinion about it. On one hand, any given OP will have in mind whether they're inclined to call the reaction/process of interest a "decomposition", and could apply decomposition or not accordingly. On the other hand, it's not a term that constrains the topic to a particular type of chemical transformation, and thus it might be too hard to clearly define a useful scope for it.

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A counter-question, possibly to help clarify our thinking: What would be a good tag excerpt for decomposition? If we can come up with an excerpt that's satisfactory to a quorum of the community, it would be a big step toward demonstrating that the tag is worth having.

Answer 3

I object for the same reasons as orthocresol (that is, I share the "contra" part of his reasoning, but not the "pro"). Reaction classes aren't really a thing anyway. Most of these questions fall under reaction-mechanism all right. For the rest we probably should have a tag like "reaction-products" or something, and use it on new questions like "what happens if I mix such-and-such chemicals".

Answer 4

I used the MATT and this tag gets a score of 0. Questions 1,2,3,8,9,10 all are answered no; questions 4,7 are answered partially and questions 5,6 are answered yes. Based on this result, I'd say this isn't a good tag to have.