Hydrochloric acid can be produced from the elements in two sequential steps at 298 K and 1 atm:
Step 1 (chlorination): H₂(g) + Cl₂(g) → 2 HCl(g)
Step 2 (dissolution): HCl(g) → HCl(aq)
Thermochemical data:
ΔH_f°(HCl(g)) = −92.3 kJ mol⁻¹ ΔH_f°(HCl(aq)) = −167.2 kJ mol⁻¹ ΔH_f° for elements in their standard states = 0 kJ mol⁻¹
The molar enthalpy of dissolution for HCl(g) to HCl(aq) is −74.8 kJ mol⁻¹ (consistent with the formation data above).
(a) Calculate the enthalpy change for Step 1 as written, producing 2 mol of HCl(g).
(b) Using the value in part (a) and the enthalpy of dissolution, determine the overall standard enthalpy change for producing 2 mol of HCl(aq) directly from H₂(g) and Cl₂(g).
(c) Is the overall process exothermic or endothermic? Quantitatively support your answer and discuss one practical implication for heat management in an industrial plant that carries out this synthesis.