Can you name examples of reactions that are endothermic and simple molecules are combined into more complex ones at the same time? Like what plants do they take heat and sunlight and they synthetize air and water into organic fuels such as glucose and ethanol. I found similar experiments made for carbon capture some call it reverse combustion, they take air and water, and with help of heat or electricity they turn it into the ethanol or glucose. So can you name similar reactions, where something similar happens? I really can’t find an answer anywhere. Please help 🙏. Thank you for taking your time to read this.

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    $\begingroup$ Is there a serious reason for not writing chemical formulas properly ? $\endgroup$ – Poutnik Jan 28 at 17:48
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    $\begingroup$ What are you really looking for ? In the beginning, you are looking for the "synthesis of $\ce{CO2 + H2O}$". Well ! this operation is carried out every day in the combustion of any fuel like gasoline, oil, petroleum, alcohol, wood, etc. It is not a synthesis and it is not endothermic. In your second sentence, you speak of a company that makes vodka out of air and water. This is non-sense, for lack of Carbon atoms. In your third sentence you speak of the synthesis of glucose out of CO2 in the lab. No labs are able to do it. Only plants can do it. I repeat : What are you looking for ? $\endgroup$ – Maurice Jan 28 at 18:06
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    $\begingroup$ "There is never time to write questions properly, but there is always much more time for their explanation." $\endgroup$ – Poutnik Jan 28 at 19:17
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    $\begingroup$ I think this question should not have been close or it might be reopened. OP should clarify if s/he put special emphasis in the word synthesis. If it is meant for reaction, then the answer is to look for the Free Energy of the process. If it is meant for a reaction organising matter and placing energy into it (at least one part of the system sees lowering of entropy), it becomes the topic of why reactions within the living kingdom are special. Not that I know the answer or I can debate it with lucidity, but the issue is interesting and opens, like in the photosynthesis chemistry community. $\endgroup$ – Alchimista Jan 29 at 9:35
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    $\begingroup$ You are right that synthesis can be taken as to build up complex things from smaller. Perhaps it was even the original meaning. However synthesis can be read as whatever reaction is conducted. So dismantling a complicated molecule into pieces of interest can be called somehow the synthesis of the latter. This said, on the light of your question as for the latter comment, I am afraid only living organisms do that. There is a question that I can't find right now, here on in physics SE, to which I have contributed full of wish but I am crystal saying that at the end the issue isn't that clear. $\endgroup$ – Alchimista Jan 29 at 15:03

Here are three examples of endothermic synthesis reactions. Heats of formation are given at 1 bar, 298.15 K. The first of these, the production of ozone, is naturally-occurring.

$$ \begin{align} \ce{3/2 O2(g) &-> O3(g)} &\quad \Delta_\mathrm{f}H^\circ &= \pu{142 kJ mol^-1}\\ \ce{N2(g) + 1/2 O2(g) &-> N2O(g)} &\quad \Delta_\mathrm{f}H^\circ &= \pu{82 kJ mol^-1}\\ \ce{1/2 N2(g) + O2(g) &-> NO2(g)}&\quad \Delta_\mathrm{f}H^\circ &= \pu{33 kJ mol^-1} \end{align} $$

  • $\begingroup$ Does this classic example count? $\endgroup$ – Ed V Jan 29 at 13:29
  • $\begingroup$ @EdV and this one: chemistry.stackexchange.com/questions/86855/… $\endgroup$ – Nilay Ghosh Jan 29 at 13:35
  • $\begingroup$ @NilayGhosh Yes! And I was kind of hoping that entropy and free energy could get an oblique nod (nothing more than that: simply name-checking them), just to indicate that enthalpies, while cool characters here, are not the entire cast of the play! $\endgroup$ – Ed V Jan 29 at 13:58
  • $\begingroup$ @theorist thank you very much for the answer. But after some research I found out that both n2o and no2 are naturally occurring too. $\endgroup$ – AverageJoe Jan 29 at 15:32
  • $\begingroup$ chemistry.stackexchange.com/questions/101691/… $\endgroup$ – Alchimista Jan 29 at 15:48

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