Timeline for example of endothermic luminescence?
Current License: CC BY-SA 4.0
18 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Oct 4, 2021 at 8:51 | vote | accept | creillyucla | ||
| Oct 4, 2021 at 6:49 | comment | added | porphyrin | Unless your photon is produced with 100% yield from P* some heat has to be produced. Only a few types of molecules such as 9-10 diphenyl anthracene appear to have almost 100% fluorescence yield. | |
| Oct 2, 2021 at 19:30 | comment | added | Poutnik | That is why I said I missed it,otherwise I would say you have not mentioned it. | |
| Oct 2, 2021 at 19:28 | comment | added | creillyucla | @Poutnik I did specify the constant volume condition in my question. Regarding your other point, whenever one has a system composed purely of reactants and no products, you will always at a finite temperature spontaneously produce products in some (possibly small) quantity, no matter the energy of the products. The entropy increase per mole of reaction diverges as the concentration of products approaches zero, which more than compensates any entropy decrease associated with the photon generation. | |
| Oct 2, 2021 at 18:52 | comment | added | Poutnik | I see, U have missed the constant volume condition. But I am not sure, if TD would be happy with decreasing entropy of environment. | |
| Oct 2, 2021 at 18:35 | answer | added | creillyucla | timeline score: 3 | |
| Oct 2, 2021 at 16:32 | comment | added | creillyucla | @Poutnik if we begin we a sample of pure reactants R, then we begin with very low entropy, so that the production of products P results in an increase of entropy which can compensate the increase from conversion of heat to light. Also note that the condition for spontaneity for a constant temperature, constant volume reaction is a decreasing Helmoltz free energy F = U - TS, not Gibbs free energy G. | |
| Oct 2, 2021 at 12:52 | comment | added | Poutnik | I guess the supposed spontaneous endothermic process may have problems with the 2nd TD law. Delta H would by positive, and due conversion of heat to radiation, Delta S would be negative. Delta G would be positive and spontaneity is ruled out. | |
| Oct 2, 2021 at 12:44 | comment | added | Ed V | No, but I do not know of any, for what that is worth. Maybe some chemiluminescence scheme, as you suggested, might do the trick. But the only ones I have heard about produce both light and heat. | |
| Oct 2, 2021 at 12:42 | comment | added | Poutnik | Is all production of light accompanied by the generation of heat? // Due nonlinearity, momentum decrease leads to lesser KE decrease than the vice versa. | |
| Oct 2, 2021 at 12:38 | comment | added | creillyucla | @EdV so you would claim that no chemical process exists possessing the energy diagram I describe above? | |
| Oct 2, 2021 at 12:37 | comment | added | creillyucla | @Poutnik the question is not whether a photon imparts a momentum kick to the atom upon leaving (though in fact it is also possible that the momentum kick acts to reduce the molecule's net momentum), but whether or not the light-producing reaction is accompanied by a net absorption of heat from its surroundings. | |
| Oct 2, 2021 at 12:29 | comment | added | Ed V | Interesting question. My first thought was simply no, but it is certainly possible to do a non-chemical version using a heat source, a thermoelectric generator and a red LED. So the desired chemical system has to convert heat energy to light energy, with non-negligible efficiency. | |
| Oct 2, 2021 at 11:55 | comment | added | Poutnik | As emission of photons must obey the momentum conservation law, it gives some momentum and related kinetic energy to the emitting atom. Even if this energy is very small, compared to mean thermal kinetic energy, it inevitably creates little heat. | |
| Oct 2, 2021 at 10:40 | comment | added | creillyucla | I did do some preliminary searching, though, not having a chemistry background, it is difficult to come up with the right search queries to find examples. I figured it would be a good question to ask a community of chemistry enthusiasts, since they might be expected to be familiar with a wide variety of different chemical reactions. | |
| Oct 2, 2021 at 10:37 | history | edited | creillyucla | CC BY-SA 4.0 |
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| Oct 2, 2021 at 1:06 | comment | added | ACR | Can you add more context and some of your own findings? | |
| Oct 1, 2021 at 20:36 | history | asked | creillyucla | CC BY-SA 4.0 |