Bond breaking, bond making and net energy transfer
≈ 48 minBond breaking, bond making and net energy transfer
Bond energy is the energy required to break a specified amount of a bond in gaseous molecules. It provides a model for estimating reaction energy changes: add energy required for bonds broken, then subtract energy released as new bonds form. The estimate is often approximate because average bond energies are used and the real environment can differ. The sign still carries a clear meaning. If more energy is released in bond formation than absorbed in bond breaking, the net ΔH is negative and the reaction is exothermic. If the balance is reversed, the reaction is endothermic.
Work it through
Imagine a reaction requiring 800 kJ mol⁻¹ to break bonds and releasing 620 kJ mol⁻¹ when products form. ΔH ≈ 800 − 620 = +180 kJ mol⁻¹. The positive sign tells you the system needs a net energy input. Do not call the process 'energy-free' merely because some bonds are formed; every reaction involves both breaking and making bonds.
Mastery target
Estimate a net enthalpy change from bond-energy totals and state the correct energy classification with its sign.
What does a bond energy value describe?
Name the key chemistry term from Bond breaking, bond making and net energy transfer that best fits the explanation and visual model.
If bond breaking requires 800 kJ mol⁻¹ and bond making releases 620 kJ mol⁻¹, what is ΔH in kJ mol⁻¹?
Which statement corrects a common misunderstanding in Bond breaking, bond making and net energy transfer?