I don't know what are the molecular reasons that two substance will form another substance.

Why oxygen molecules can form to ozone molecules? Why hydrogen and oxygen makes water? What are the physical foundations for it? Is it possible to explain it with quantum mechanics?

EDIT: There are models for chemical reactions in terms of continuum mechanics (it is called "Mixture Theory"). But I don't understand Mixture Theory!

I know basics of continuum mechanics, but NO continuum mechanics of mixtures which can react with each other. Can someone explain this pdf:



closed as too broad by David Hammen, user36790, ACuriousMind, Jon Custer, Qmechanic Sep 24 '16 at 14:20

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Do you want a quantum mechanics explanation (if one exists)? Or would any explanation be sufficient? $\endgroup$ – tpg2114 Sep 23 '16 at 21:59
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    $\begingroup$ @Gert I disagree -- statistical mechanics and the view of collisions strong enough to excite vibrational modes until they bonds are broken is an entirely appropriate physics viewpoint. And so is QM for that matter. I think it's perfectly fine on topic here, but I was just seeking clarification on the last line -- is that a requirement of the answer (to use QM) or is it just something that would be nice. $\endgroup$ – tpg2114 Sep 23 '16 at 22:15
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    $\begingroup$ physics.stackexchange.com/q/35408 has answers that provide quite a good insight into covalent bonding. $\endgroup$ – Gert Sep 23 '16 at 22:36
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    $\begingroup$ Frankly someone asking a question like this shouldn't be thrown into the deep end of the pool. Quantum mechanics is overboard here. // Basically chemical reactions are driven by energy. If the products contain less energy than the reactants then the reaction is spontaneous. If the products contain more energy then some form of energy input is required to drive the reaction. Ozone forms in the upper atmosphere because UV rays from the sun create excited oxygen molecules. In the absence of the UV energy oxygen molecules won't spontaneously create ozone. $\endgroup$ – MaxW Sep 23 '16 at 22:38
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    $\begingroup$ Voted to close - This question now mutated into wanting an explanation of a 124 page pdf file. The paper would need an understanding of physical chemistry before it would make sense. You can't explain p-chem in a couple of paragraphs. $\endgroup$ – MaxW Sep 24 '16 at 0:26

Basically, forming chemical bonds releases energy. E.g. two atoms join together to make a chemical bond between them and release energy. Thereby, atoms/ molecules join together to get the stability (lesser the energy, higher the stability). You can do a simple calculation, calculate the total energy stored in one mole of Oxygen molecules (bond energy between O-O, per mole), two moles of hydrogen molecules (bond energy between H-H, per two moles), Then find out the energy stored in two moles of water molecules (bond energy between H-O, per two moles). You will see that the reaction of forming water is exothermic.

As a summary

at standard conditions, this reaction releases 285.8 kJ of energy.

H2(g) + 1/2 O2 -> H2O (l), enthalpy = -285.8 kJ per mol

negative value tells that the heat is released

This is why mixing HCl and NaOH releases heat. So overall, the physical foundation is gaining stability!

  • $\begingroup$ Why heat is in some reaction a lot faster released than in other reactions? $\endgroup$ – kryomaxim Sep 23 '16 at 22:33
  • $\begingroup$ @kryomaxim: are you asking why some reactions are faster than others or why are some are more exothermal than others? $\endgroup$ – Gert Sep 23 '16 at 22:39
  • $\begingroup$ I am also asking whether some reactions are faster than others. $\endgroup$ – kryomaxim Sep 23 '16 at 22:41
  • $\begingroup$ @Kosala. This is why mixing HCl and NaOH releases heat Can you explain why? $\endgroup$ – Gert Sep 23 '16 at 22:41
  • $\begingroup$ @kryomaxim - I am also asking whether some reactions are faster than others. Really not easy to explain in a few words. It's hard to summarise the theory of chemical kinetics in a few sentences. It all starts with collision theory. Reactions take place when molecules collide at sufficiently high energies. The more of these reactive collisions per unit of time, the faster the reaction will proceed. $\endgroup$ – Gert Sep 23 '16 at 22:45

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