Two liquid fuels—propanol (C3H7OH) and propanal (C3H6O)—are being considered for use in a portable combustion device. Relevant average bond energies (kJ mol−1) are provided in Table 2.
Table 2. Selected Average Bond Energies
C–H 413 C–C 348 C–O 358 C=O 743 O–H 463 O=O 498 C=O (in CO2) 799 O–H (in H2O) 463
Complete combustion reactions (balanced):
Propanol: C3H7OH + 9⁄2 O2 → 3 CO2 + 4 H2O
Propanal: C3H6O + 4 O2 → 3 CO2 + 3 H2O
Molar masses (g mol−1):
C3H7OH = 60.1 C3H6O = 58.1
a) Use the bond energies in Table 2 to estimate ΔH (in kJ mol−1) for the combustion of each fuel. Show all intermediate steps.
b) Convert each molar enthalpy value to energy released per gram of fuel (kJ g−1).
c) Based on your calculations in part (b), determine which fuel releases more energy per gram. State one practical implication of this difference for portable combustion devices.