Graphite and Diamond question!?

Question

(i) Explain why the transition diamond --> graphite is expected to be thermodynamically favoured. (DeltaH = -1.9kJ/mol)

(ii) Explain why, despite this thermodynamic tendency, diamond exists?

Answer 1

The reaction is ever so slightly exothermic, so is favoured in that way. But reorganising the atoms from one solid giant lattice structure into another has such a huge activation energy that to all intents and purposes the reaction doesn't happen - except under extraordinary conditions of temperature and pressure.