The enthalpy of combustion of propane, graphite and dihydrogen at...

The combustion reaction can be written as follows,

${C}_{3}{H}_{{8}_{\left(g\right)}} + 5{O}_{2}\overset{}{\to}3{CO}_{2} + 4{H}_{2}O; ∆ H = - 2220 . 0kJ{mol}^{- 1}$

${C}_{graphite} + {O}_{2\left(g\right)}\overset{}{\to}{{CO}_{2}}_{\left(g\right)}; ∆ H = - 393 . 5kJ{mol}^{- 1}$

${{H}_{2}}_{\left(g\right)} + \dfrac{1}{2}{O}_{2\left(g\right)}\overset{}{\to}{H}_{2}{O}_{\left(l\right)}; ∆ H = - 285 . 8kJ{mol}^{- 1}$

Now, the formation reaction of propane is

$3{C}_{\left(graphite\right)} + 4{H}_{2\left(g\right)} \to {C}_{3}{H}_{8\left(g\right)} ∆ {H}_{f} = 3 ∆ {H}_{C}^{°}\left(graphite\right) + 4 ∆ {H}_{C}^{°}\left({H}_{2\left(g\right)}\right) - ∆ {H}_{C}^{°}\left(propane\right) ∆ {H}_{f} = 3 \times \left(- 393 . 5\right) + 4 \times \left(- 285 . 8\right) - \left(- 2220\right) = - 103 . 7kJ{mol}^{- 1}$