Nitrosyl chloride decomposes according to the balanced equation
2 NOCl(g) → 2 NO(g) + Cl₂(g) ΔH°rxn = +200 kJ at 298 K
Average bond energies (kJ mol⁻¹):
N=O 607
Cl—Cl 243
N—Cl ?
(a) Identify which bond types are broken and which are formed in the decomposition. For each type, state the number of bonds involved per mole of reaction.
(b) Explain why the N=O bond energy does not need to be included explicitly in the overall energy change, even though N=O bonds are present in both reactants and products.
(c) Derive an expression for ΔH°rxn in terms of the unknown N—Cl bond energy, B(N—Cl), and calculate its numerical value.
(d) The decomposition of NOCl is endothermic. Discuss, in terms of bond strengths, why removal of chlorine from the nitrosyl chloride molecule requires energy despite simultaneous formation of Cl₂.