Consider the reaction written below, carried out in the gas phase at 298 K and 1 atm.
H2(g) + Cl2(g) → 2 HCl(g)
Average bond energies (298 K):
• H–H 436 kJ mol⁻¹
• Cl–Cl 242 kJ mol⁻¹
• H–Cl 431 kJ mol⁻¹
Answer the following questions. Show all reasoning, include units with each numerical result, and clearly indicate the sign of each energy term.
(a) For one mole of the reaction as written, list the type and number of each bond that must be broken and the type and number of each bond that will be formed.
(b) Calculate the total energy required to break all bonds in the reactants.
(c) Calculate the total energy released when all product bonds are formed.
(d) Determine ΔH for the reaction. State whether the reaction is exothermic or endothermic and justify your choice using the calculated energy values.
(e) Calculate the enthalpy change per mole of HCl produced and explain how this value compares to the ΔH for the reaction as a whole.