Why do carbon allotropes have small standard enthalpies of formation?

[James Essig]

TL;DR

I am curious about the standard enthalpies of formation of carbon nanotubes, diamond, carbon buckyballs, graphene, etc.

I am curious about the standard enthalpies of formation of carbon nanotubes, diamond, carbon buckyballs, graphene, etc. I read from physics forums that the standard enthalpies of formation of these allotropes of carbon are small. However, since diamond is fabricated naturally under extreme pressures and high temperatures at depths of at least dozens of kilometers below the Earth's surface, small magnitude enthalpies of formation do not make much sense to me for diamond and thus also for the other exotic carbon allotropes I mentioned above all of which have similar bulk moduli. If anyone can offer some information on this subject that would be great. I've looked at some of the papers available on line for this kind of stuff but I find them obtusely technical. I am not adverse to reading highly technical papers of the subject so long as I know they are rigorously peer reviewed and of high research qualities. By molar standard enthalpies of formation I am assuming that the molar metric is for one mole of carbon atoms and not, say, one mole of carbon nanotubes and the like.

 

[TeethWhitener]

The enthalpy of formation of diamond is small (I want to say it’s something like 2.5 kJ/mol relative to graphite), but the energy barrier between diamond and graphite is huge (something like 1000kJ/mol). So getting from diamond to graphite requires a LOT of energy, even if thermodynamically the energies aren’t that different.

 

[James Essig]

Thanks for the reply TeethWhitener. That is useful information.