Enthalpy of combustion of  diamond is 395 kJ/mole and Enthalpy of combustion of graphite is 393 kJ/mole. Enthalpy change when 24 grams of graphite converts to 24 grams of diamond is

$$\begin{gathered} \mathrm{Combustion} \mathrm{is} \mathrm{always} \mathrm{exothermic}, ∆\mathrm{H}=-\mathrm{ve}; \\ \mathrm{C}\left(\mathrm{diamond}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right) \to {\mathrm{CO}}_2\left(\mathrm{g}\right); ∆\mathrm{H}=-395\mathrm{kJ} -\mathrm{I} ; \\ \mathrm{C}\left(\mathrm{graphite}\right)+ {\mathrm{O}}_2\left(\mathrm{g}\right) \to {\mathrm{CO}}_2\left(\mathrm{g}\right); ∆\mathrm{H}=-393\mathrm{kJ} -\mathrm{II}; \\ \mathrm{Eq} \mathrm{II} - \mathrm{Eq} \mathrm{I} \\ \mathrm{C}\left(\mathrm{graphite}\right)\to \mathrm{C}\left(\mathrm{diamond}\right); ∆\mathrm{H}=+2\mathrm{kJ}/\mathrm{mole} \\ 12 \mathrm{grams} 2 \mathrm{kJ} \\ 24 \mathrm{grams} 4 \mathrm{kJ} \end{gathered}$$