Answer :
Final answer:
Correct option: a) -93 kJ/mol. The standard molar enthalpy of formation (ΔHf) for HCl(g) is – 93 kJ/mol, which is determined by dividing the overall reaction enthalpy ΔHrxn of – 186 kJ by the 2 moles of HCl formed in the reaction.
Explanation:
The value of the standard molar enthalpy of formation (ΔHf) of HCl(g) can be determined from the reaction:
H2(g) + Cl2(g) → 2HCl(g)
The given ΔHrxn (enthalpy change of the reaction) for this exothermic reaction is −186 kJ. This energy change corresponds to the formation of 2 moles of HCl(g), thus each mole of HCl formed releases half of the energy provided by the reaction.
ΔHf per mole of HCl(g) = −186 kJ / 2 moles
= −93 kJ/mol
This is close to the value cited in Appendix G, which provides a standard molar enthalpy of formation for HCl(g) of −92.307 kJ/mol. Therefore, the correct answer is a) −93 kJ/mol.
