با توجه به واکنش‌های داده شده، طبق قانون هس خواهیم داشت:

$\begin{align}
  & 1)\frac{3}{2}{{H}_{2}}O(l)\to \frac{3}{2}{{H}_{2}}(g)+\frac{3}{4}{{O}_{2}}(g)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta {{{{H}'}}_{1}}=429kJ \\
 & 2)C(s,gerafit)+\frac{3}{2}{{H}_{2}}(g)\to \frac{1}{2}{{C}_{2}}{{H}_{6}}(g)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta {{{{H}'}}_{2}}=-42kJ \\
 & \underline{3)\frac{1}{2}{{C}_{2}}{{H}_{6}}(g)+\frac{7}{4}{{O}_{2}}(g)\to C{{O}_{2}}(g)+\frac{3}{2}{{H}_{2}}O(l)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta {{{{H}'}}_{3}}=-780kJ} \\
 & C(s)+{{O}_{2}}(g)\to C{{O}_{2}}(g)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta H=-393kJ \\
\end{align}$

بنابراین مقدار حاصل از سوختن کامل یک گرم گرافیت خالص بر حسب کیلوژول برابر خواهد بود با:

$?kJ=1g\,C\times \frac{1mol\,C}{12g\,C}\times \frac{393kJ}{1mol\,C}=32/75kJ$