Question

The bond energies are: C-H 416 kJ/mol; C-C 356 kJ/mol; O=O 498 kJ/mol; C=O 803 kJ/mol; H-O 467 kJ/mol. Which is the net energy released on complete combustion of propane?

Answer 1

To calculate the net energy released during the combustion of propane, the bond energies are used to sum the energy required to break bonds in the reactants and the energy released forming bonds in the products, then subtracting the former from the latter.

Step-by-step explanation:

To calculate the net energy released on the complete combustion of propane, we must consider the bond energies provided and the balanced chemical equation for the combustion of propane:

C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)

For the reactants, we need to break 8 C-H bonds and 3 C-C bonds in propane, and also 5 O=O bonds in oxygen molecules. For the products, we form 12 C=O bonds in carbon dioxide and 8 O-H bonds in water. Using the given bond energies:

• Bonds broken (reactants): 8(C-H) + 3(C-C) + 5(O=O) = 8(416 kJ/mol) + 3(356 kJ/mol) + 5(498 kJ/mol)
• Bonds formed (products): 12(C=O) + 8(O-H) = 12(803 kJ/mol) + 8(467 kJ/mol)

The calculated energies must be summed for both the reactants and products, then subtract the total energy required to break the bonds from the total energy released in forming new bonds to find the net energy change.