Chemistry – Chemical energetics - Exothermic and endothermic reactions | e-Consult

Answer:

The balanced combustion reaction of methane is: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

First, we need to calculate the total energy required to break the bonds in the reactants and the energy released when forming the bonds in the products.

Reactants:

• CH₄: 4 C-H bonds x 413 kJ/mol = 1652 kJ/mol
• O₂: 2 O=O bonds x 498 kJ/mol = 996 kJ/mol (Note: O=O bond energy is typically 498 kJ/mol, but we'll use the provided C=C as a proxy for a reasonable estimate in this context)

Products:

• CO₂: 2 C=O bonds x 799 kJ/mol = 1598 kJ/mol
• H₂O: 2 O-H bonds x 463 kJ/mol = 926 kJ/mol

Total energy required to break bonds = 1652 kJ/mol + 996 kJ/mol = 2648 kJ/mol

Total energy released when forming bonds = 1598 kJ/mol + 926 kJ/mol = 2524 kJ/mol

Enthalpy change of reaction = Energy released - Energy required to break bonds

ΔH = 2524 kJ/mol - 2648 kJ/mol = -124 kJ/mol

Therefore, the enthalpy change of combustion of methane is -124 kJ/mol.