Hess's Law Problem

Question

3. Calculate the enthalpy of combustion for propane, C3H8, if:

ΔHof for propane = -104 KJ/mole

ΔHof for liquid water = -286 KJ/mole

ΔHof for gaseous carbon dioxide = -393.5 KJ/mole

Solve for the enthalpy of combustion using Hess’s law, and then solve for the enthalpy of combustion using the summation equation for heats of formation.

Answer 1

C₃H₈ + 5O₂ ==> 3CO₂ + 4H₂O

∑products - ∑reactants

3x(-393.5) + 4x(-286) - (-104) = -1181 + -1144 + 104 = -2221 kJ