Wikipedia:Reference desk/Archives/Science/2019 July 5

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July 5

chemistry clarification

Since two different compounds always have at least one different chemical properties (i.e., chemical reactions).

Now if isomers are different chemical compounds, then how do i prove that any two isomeric structures always have different set of chemical reactions?

In the case of optical isomerism where there a little change in orientation in space occurs, i don't think any of its reaction got effected, even if it happened with one then what's the surety for such to all. Suyogya1 (talk) 14:25, 5 July 2019 (UTC)

Enantiomers might have different rates of reaction (see asymmetric induction), and often have different covalent and/or ionic binding affinities (affecting things like solubility, chromatographic mobility, etc.) against other chiral substances. Be careful not to think that "chemical reactions" are the only aspect of a chemical that are "properties" of that chemical. DMacks (talk) 14:46, 5 July 2019 (UTC)

It's also important to note that some of our traditional "boundaries" we set in these definitions are arbitrary anyways. We say things like dissolving and phases changes are "physical" and not "chemical" changes, but that's not because there's a fundamental difference between those changes and other "chemical" changes. Humans need to create categories to break our world into more manageable pieces, but when you really start to look at what's going on, there's a lot less different at the edge cases than we presume. It's all breaking and forming bonds, that is working against or with electrostatic forces. What we call a "molecule" or an "ion" or a "chemical bond" or a "intermolecular bond" are all differences in quantity, not in character. It's all the same thing at the basic level.--Jayron32 17:08, 5 July 2019 (UTC)

Molecular compounds

1. Why do we use nona- rather than ennea- for 9??
2. Why do we use mono- for the second word of an element's name but not the first??
3. Why do we treat hydrogen like its atomic number is 7 1/2 for the purpose of ordering it??
4. Why can krypton and xenon (which are noble gases) form compounds?? Georgia guy (talk) 17:47, 5 July 2019 (UTC)

(Please make sure you know exactly what I mean when it comes to question #3. Hydrogen has the atomic number of 1, but for the purpose of ordering it in binary molecular compounds, it's more like its atomic number is 7 1/2, only on the highest row rather than the second highest row.) Georgia guy (talk) 17:47, 5 July 2019 (UTC)

3) Note that hydrogen was placed in 2 positions on the Mendeleev Periodic Table of the Elements: [1]. SinisterLefty (talk) 17:57, 5 July 2019 (UTC)

The answer to #4 can be found in the Wikipedia article titled noble gas compound. The answer to the other three is the same basic answer: Language is not a rigid, perfectly consistent system. The language of chemistry evolved, over many centuries, like other languages have, and it is not, has not been, and likely will never be, a perfectly self-consistent system. For example, on the issue of not using "mono" for the first element, that is a historical artifact of how chemical compound formulas were determined: you took something and burned it in oxygen, then figured out the molar ratio of that stuff to oxygen. That would give you the prefix for the oxide portion, and the first word was always assumed to be one. There were even fractional prefixes like sesquioxide used in cases like Fe2O3. The system of using prefixes for the first element came about over a century after these earlier systems existed, due to a new a different understanding of how chemistry works. Anytime you graft a new system on to an older system, there are GOING to be inconsistencies. After all, we still use words like "ethane" and "propane" and not "diane" and "triane". Why? Because there's no benefit from changing from the words we already used for centuries. Language will always be messy.--Jayron32 18:03, 5 July 2019 (UTC)

Issue 1 is even more widespread than "chemistry"...polygons are octagon but nonagon only has as a presumably rare synonym enneagon. Chemistry presumably followed the pre-existing naming of "a series with increasing numbers of things". Jayron32 is right...language is organic (pun intended). DMacks (talk) 19:02, 5 July 2019 (UTC)

I laughed, but what does that final sentence mean?? Georgia guy (talk) 19:08, 5 July 2019 (UTC)

See wikt:organic adjective definition #9. The alkyl series n≥5 doesn't follow a single language's prefixes (the question is about why not all Greek, but instead mixed with some Latin). But that alkyl series exactly matches the polygon names. So the chemistry actually does exactly build on an antecedent, that itself isn't single-language, but presumably was built up over time from...dunno. DMacks (talk) 20:52, 5 July 2019 (UTC)

Bottle Cap Challenge

In the recently trendy Bottle Cap Challenge a bottle cap has been unscrewed particularly by a roundhouse kick, ice skate kick and gymnastic juggling club. My understanding is that in all instances the cap has been slightly loosened beforehand, as otherwise it would be nearly impossible due to lever principle (where after fixing the bottle a strong grasping force is applied in addition to rotation). What physics comes into play here? 212.180.235.46 (talk) 20:16, 5 July 2019 (UTC)

You need a certain amount of torque to open the bottle cap (far less if the seal has been broken), and that is force times the distance from the center of the cap. Any kind of striking motion will have the problem that that force is applied over a very small area, creating high pressure, breaking the bottle or ripping the cap open. When using your hand to open a bottle cap, the force is distributed evenly over a much wider area. There's also something called an impact, where the force is applied so quickly the object doesn't have time to absorb the force and distribute it evenly by deforming (bending) slightly, and instead fractures. An example of this is when high speed photography is used on a bullet going through a rubber sheet. Instead of stretching, the rubber shatters like glass. SinisterLefty (talk) 20:31, 5 July 2019 (UTC)

You need torque indeed. The trouble is, you don't have torque by applying a single force, you need 2. The force from the kick is pretty much unlimited. The second force comes from the way the bottle is held. If it is firmly held by a sidekick (pun intend), glued, or whatever, then the force will be just equal and opposite to the force coming from the kick, and it will work; besides, the kicker won't have to be so precise, if he kicks too far, the second force will keep his foot in place. If not firmly held, chance are the bottle will tip over; to avoid that, you'll need a heavy bottle (ie: glass, not plastic) for maximum inertia, with a metal cap that has low friction against the glass. Notice many video show the cap of the bottle and you dont know if and how how it is held. Sometime the sidekick, holding the bottle (and even applying is own strength against the kicker shoe), is on the video. Gem fr (talk) 22:19, 5 July 2019 (UTC)

• Mostly momentum, impulse and inertia. Torque only comes into it later.

As noted, it takes two forces to produce a torque. These come from whatever hits the cap, and from the bottle itself. These should give rise to a couple on the cap, which gives a torque, which causes rotation. If it's not a balanced couple, the bottle falls over. But before you get that couple, you have a (quite complicated) process where the momentum of the foot / shoe sole hits the cap and delivers an impulse. As all of these things are also flexible, a lot goes on before it resolves into a simple couple.

You can analyse this (high school Newtonian mechanics) as a rigid bottle and an impulse from the foot. You've simplified this by making the bottle rigid rather than elastic. But the real situation is going to be more complicated, and tricky. Andy Dingley (talk) 11:22, 6 July 2019 (UTC)