I hope that the title of the question is not completely wrong or misleading, however I couldn't think up of a better one.

I have a follow up question to this one. If we look at the following reaction, $$\ce{C + O2 -> CO2}$$

we are taught that gases like oxygen (looking at the reactants), when not part of a compound, always appear in molecular form.

But if to follow one of the answers in the referred question, the reaction has a little more to it. I quote:

carbon, as normally found in nature as graphite, consists of a molecular solid with every carbon bonded to several other carbons. The reaction C + O2 is shorthand for solid carbon plus oxygen gas, so the reaction involves breaking lots of C-C bonds and O=O bonds resulting in CO2. You have to account for all the bonds broken and formed to know the energy difference.

Why is this fact not accounted for in the reaction $\ce{C + O2 -> CO2}$, in other words, why do we 'allow' carbon to be a free atom (although it's not, in the form of graphite) and 'demand' that the oxygen is in a molecular form? I do assume that chemical reactions are a form of abstraction, that is, we say that regardless of where that carbon atom comes from, it will react with the oxygen molecule into a carbon dioxide, but I still don't understand why we then apply those molecule constraints to oxygen.

To be more explicit about it: the energy spent to break the C-C bonds in the graphite crystal is not easily readable from the reaction, while the fact that the O=O bonds are split, and therefore energy is input into the system, is.

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    $\begingroup$ You are right in that it's kinda illogical. Then again, what notation would you propose for covalent solids like graphite? $\rm C_\infty$? $\endgroup$ Jun 20 '17 at 12:49
  • $\begingroup$ Chemistry is complicated. You want to capture all of the nuances of a reaction with a few scribbles? $\endgroup$
    – Zhe
    Jun 20 '17 at 13:39
  • $\begingroup$ @Zhe I'm not really out to capture all of the nuances of a reaction with a few scribbles. But I do try to point out inconsistencies where I see them, and I think the 'handling' of the C and the O elements in this equation is inconsistent. Also, although when getting into the topic of energy, discussion usually moves away from chemistry into physics, I think (and my book seems to point it out whenever possible) that the flow of energy involved in a reaction is a very important part of it, which led me to wonder why this is not notated in a better way. I think this is a justified consideration. $\endgroup$
    – user46667
    Jun 20 '17 at 13:49
  • $\begingroup$ @Zhe also, excuse me if I'm being somewhat direct here, there's not much I can learn from "subject x is complicated". That's a given. Every subject is complicated as you delve more into it. As someone with background in computer science, when I don't understand a problem, I try to break it down to simpler problems for which I can then fashion solutions and combine into a solution of the larger problem, which would be the resulting algorithm. I don't know how much that approach is applicable to chemistry, but I am trying to understand things by breaking them down to "why is X the way it is". $\endgroup$
    – user46667
    Jun 20 '17 at 14:01
  • $\begingroup$ OK, but generations of chemists have settled on this notation as a compromise between what is feasible/simple and what is correct. I understand that you might not agree with that, but you shouldn't definitely go with it for now. Physics does that, too, since in general physical systems in real life are a lot more complicated than the simple model systems we study. $\endgroup$
    – Zhe
    Jun 20 '17 at 14:02

The reaction, described in the form given in the original question, i.e.

$$\ce{C + O2 -> CO2}$$

simply conveys that each formula unit of carbon reacts with one formula unit of oxygen to yield one formula unit of carbon dioxyde. As such, for example, useful to balance how many grams of carbon may be burnt with $\pu{22.7 L}$ of oxygen. As such, yes indeed, it is a limited representation. In an analogy, it is like book keeping; (within reason) is does not matter how you paid at a garage (cash, debit or credit) to get your car back -- but to satisfy both sides, it has to be balanced.

This view contrasts with many organic reaction equations as reaction mechanisms which are intentionally drawn with further detail like this:

enter image description here


Here, the how is important, and consequently outlined with more attention. As if you would need to explain an apprentice how the teeth of a gear have to be adjusted in face, pitch, flank, etc. to transmit the force from the engine to the wheels.