Cgraphite + O2(g) → CO2(g)
ΔH = −94.05kcal mol−1
Cdiamond + O2(g) → CO2(g); ΔH = −94.50 kcal mol−1 therefore
Graphite is the stabler allotrope
Heat energy is also involved when one allotropic form of an element is converted in to another graphite is the stabler is the stabler allotrope because the heat of transformation of Cdiamond → Cgraphite
(i) C(dia) + O2(g) = CO2(g) ΔH = −94.5Kcal
(ii) C(graphite) + O2(g) = CO2(g) ΔH = −94.0Kcal
ΔH(transformation) = −94.5 − (−94.0)
= 0.54 Kcal.