The equation in accordance with the definition of standard heat of formation of CO₂ (g) is

${\mathrm{C}}_6{\mathrm{H}}_{6\left(\mathrm{l}\right)}+7\frac{1}{2}{\mathrm{O}}_{2\left(\mathrm{g}\right)}\to 6{\mathrm{CO}}_{2\left(\mathrm{g}\right)}+3{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}$

C(graphite) + O2 (g) ® CO2 (g)

CO(g) +$\frac{1}{2}{O}_2$(g) ® CO₂(g)

CH₄ (g) + O₂ (g) ® CO₂ (g) + 2H₂O(l )