Solution: Diamond and graphite are two crystalline forms of carbon. At 1 atm and 25°C, diamond changes to graphite so slowly that the enthalpy change of the process must be obtained indirectly. Using equations from the list below, determine ΔH  for C(diamond) ⟶ C(graphite)
(1) C(diamond) + O₂(g) ⟶ CO₂(g)          ΔH = −395.4 kJ
(2) 2CO₂(g) ⟶ 2CO(g) + O₂(g)              Δ H = 566.0 kJ
(3) C(graphite) + O₂(g) ⟶ CO₂(g)          Δ H = −393.5 kJ
(4) 2CO(g) ⟶ C(graphite) + CO₂(g)      ΔH = −172.5 kJ