Graphite is the most stable state of carbon and its ∆Hf∘ is considered as zero. ( ∵ has more van der Waals' force) also ∆Hf∘ for C60>∆Hf∘ for diamond. ∆Hf∘ values of graphite, diamond and C60 are 0,1.9 and. 38.1kJmol−1 and ∆Hf∘ values are in order. Fullerene > Diamond > Graphite.