A stacked-bar visualization compares bond-energy contributions (heights proportional to average bond energy) for each molecule in the reaction
H₂(g) + Cl₂(g) → 2 HCl(g)
Average bond-energy values represented on the bars are:
• H–H: 436 kJ mol⁻¹
• Cl–Cl: 242 kJ mol⁻¹
• H–Cl: 431 kJ mol⁻¹
Assume each bar height exactly equals the corresponding numerical value given above.
(a) List the total energy associated with bonds that must be broken in the reactants and the total energy associated with bonds that are formed in the products. Show how you arrived at each total.
(b) Calculate the enthalpy change, ΔH, for the reaction as written. Include the appropriate sign and units.
(c) Interpret your result from part (b) in terms of heat flow between the reacting system and its surroundings at constant pressure.