Timeline for Is Bond Formation "Strictly" Exothermic?
Current License: CC BY-SA 3.0
11 events
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| Nov 22, 2018 at 18:20 | comment | added | Martin - マーチン♦ | @Mithoron Yes, tricky it is indeed. And obviously there is room for debate, or at least more elaboration. If I had time I'd go over that again, but I simply cannot do it. | |
| Nov 22, 2018 at 16:16 | comment | added | Mithoron | Well, this is getting tricky if one gets into details. Hmm, maybe you did well not going the path of Dave. Yes, bond creation proper, even in He2 dication is exothermic. There's the thing that closing two He+ requires a lot of energy, much more then bond releases, that means that molecule is endothermic, but not bond itself. That means your answer is OK, but there's a good reason for "controversies". | |
| Apr 13, 2017 at 12:57 | history | edited | CommunityBot |
replaced http://chemistry.stackexchange.com/ with https://chemistry.stackexchange.com/
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| Jul 30, 2014 at 20:58 | vote | accept | Dissenter | ||
| Jun 13, 2014 at 16:04 | comment | added | Martin - マーチン♦ | @Dave I am not comparing anything with anything else, I am just quoting the IUPAC Goldbook. This definition is complete in a concise and theoretical way. And with this given, the BDE is always positive. Experimentally you do not need to actually break the bond, you can derive it from spectroscopy. Thank you for the literature. As for the 'bonds' in the transition states, they do not fit within the definition of bonds or chemical bonds. | |
| Jun 13, 2014 at 15:16 | comment | added | DavePhD | Martin, it does have to do with a reaction being exothermic or endothermic, because you need to define another state that you are comparing to. Here you are comparing methane to methyl radical and hydrogen radical, which is a specific reaction. Weak bonds do form between noble gas atoms: scitation.aip.org/content/aip/journal/jcp/98/4/10.1063/1.464079 sciencedirect.com/science/article/pii/S0009261401010880# What about the bonds of trigonal bipyramidal transition states? en.wikipedia.org/wiki/Transition_state Do they require energy to break? | |
| Jun 13, 2014 at 15:01 | comment | added | Martin - マーチン♦ | Admittedly they are very, very small, but not negligible. There are weaker forces at play, i.e. London Dispersion and van der Waals. These are also part of the reason, why noble gases can be liquid close to zero Kelvin. | |
| Jun 13, 2014 at 14:08 | comment | added | Dissenter | What do you mean noble gases have a non-zero dissociation energy? How can non-bonded elements have "dissociation" energies? | |
| Jun 13, 2014 at 10:26 | comment | added | bobthechemist | +1 for bringing up the need to consider bond breaking as well as bond breaking when determining whether or not a reaction is exothermic. | |
| Jun 13, 2014 at 9:21 | history | edited | Martin - マーチン♦ | CC BY-SA 3.0 |
added another paragraph adressing noble gas dimers
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| Jun 13, 2014 at 8:47 | history | answered | Martin - マーチン♦ | CC BY-SA 3.0 |