Using the bond energies provided, calculate the energy change for the reaction where 1 mole of CH4 reacts with 2 moles of O2 to produce 1 mole of CO2 and 2 moles of H2O. The bond energies are: C-H = 412 kJ/mol, O=O = 498 kJ/mol, C=O = 799 kJ/mol, and O-H = 463 kJ/mol.

Confusing bond‑energy calculations with reaction‑profile interpretation

Students think that the shape of a reaction profile can be used to calculate the exact energy change of a reaction, or that the activation energy shown on the profile is the same as the bond energies used in calculations.

Explain that a reaction profile is a qualitative diagram showing the relative energies of reactants, transition state and products, and that it cannot provide numerical bond‑energy values. Bond‑energy calculations use tabulated average energies for specific bonds to determine the overall energy change, while a reaction profile only indicates whether a reaction is exothermic or endothermic and the relative size of the activation energy.