Two different reactions are analyzed using average bond energies

CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics

Problem

Two different reactions are analyzed using average bond energies. For Reaction A, breaking all reactant bonds requires

1640\ \text{kJ}

, and forming all product bonds releases

1780\ \text{kJ}

. Which statement correctly characterizes Reaction A? (a) Reaction A is endothermic because

1640\,\text{kJ}

must be absorbed to break the reactant bonds. (b) Reaction A is endothermic because

1780\,\text{kJ}-1640\,\text{kJ}=140\,\text{kJ}

must be supplied to the system. (c) Reaction A is exothermic because

1780\,\text{kJ}-1640\,\text{kJ}=140\,\text{kJ}

of energy is released overall. (d) Reaction A is endothermic with

\Delta H=+3420\,\text{kJ}

because energy is absorbed in both bond-breaking and bond-forming steps.