Study the reactions. C (s)+O2 (g)→CO2 (g) ΔH=−394 kJ
H2 (g)+12O2 (g)→H2O (l) ΔH=−286 kJ
3C (s)+4H2 (g)→C3H8 (g) ΔH=106 kJ
Target Reaction:

C3H8 (g)+5O2 (g)→3CO2 (g)+4H2O (l)ΔH= ?
What is the enthalpy change of the target reaction?

Explanation:

To find the enthalpy change of the target reaction, we can use Hess's Law.

Reversing the third reaction yields:

Multiplying the first reaction by three yields:

Multiplying the second reaction by four yields:

Adding all equations yield:

Hence, the enthalpy change of the target reaction is -2426 kJ.