Question

The reaction for making ammonia is N₂ + 3H₂ → 2NH₃. Use the bond energy table from the lesson to compare the energy needed to break reactant bonds with the energy released when product bonds form. Explain if this reaction is endothermic or exothermic based on this comparison. Write your answer in 1-2 sentences.

Answer 1

Using bond energies: bonds broken = N≡N (≈945 kJ) + 3×H–H (3×436 = 1308 kJ) = 2253 kJ; bonds formed = 6×N–H (6×391 = 2346 kJ) released. Because more energy is released forming N–H bonds than is required to break the reactant bonds, the reaction is exothermic (net ≈ −93 kJ per mole of N₂ reacted, i.e., per reaction as written).