Question

Enthalpy of formation of HF and HCl are -161 kJ and -92 kJ respectively. Which of the following statements is incorrect ?

• A. The affinity of fluorine to hydrogen is greater than the affinity of chlorine to hydrogen
• B. HF is more stable than HCl
• C. HCl is more stable than HF
• D. HF and.HCl are endothermic compounds

Answer 1

Answer: (C)

Compound for which $\Delta H_f$ is negative is more stable than the compound for which $\Delta H_f$ is positive. In other words, exothermic compounds are more stable than endothermic compounds.
Further, for exothermic compound, more the heat evolved during the formation of a compound from its elements, more stable it is. As such HF with $\Delta H_f$ = -161 kJ is more stable than HC1 with $\Delta H_f$ = -92 kJ