[jsmith613]

Carbon (diamond) --> Carbon (graphite). -1.9 kJ/mol.

Why does this reaction show graphite is more stable.
Why does this reaction prove diamond is not slowly turning into graphite?

thanks

[Jzalkm]

for 1st question, an energy profile diagram showing energy of diagram and graphite would help.

[Jorriss]

It doesn't quite prove it.

If a reaction is thermodynamically stable gibbs free energy is negative.

dG=dH-TdS

For the conversion from graphite to diamond or vice versa the change in entropy is roughly zero so we can approximate dG as dH.

Here, dH is negative so the reaction will occur spontaneously ie it is more stable.



I don't know if you're in gen chem I, II or HS so let me know if you are not familiar with gibbs free energy.

[igloo5080]

Given that the entropy change from one mole of an solid allotrope (diamond) into one mole of another solid allotrope solid (graphite) is bound to be very small, the enthalpy change alone can be taken as a predictor of the direction of spontaneous change. However, although calculations will show that graphite is thermodynamically more stable than diamond this has no bearing on the kinetics of the process.

Diamond is thermochemically unstable relative to graphite, but is kinetically stable nevertheless.