Question

Heat of neutralization of HF is
(A) 57.32kJ
(B) >57.32kJ
(C) <57.32kJ
(D) None of these

Answer 1

Hint: Hydration energy of an element means the energy released when it forms a strong covalent bond with water molecules during hydration reaction. This energy is released and hence it is an exothermic reaction. If the element has more hydration enthalpy, it impacts on the enthalpy change of neutralization.

Complete step by step solution:
To produce one mole of water when solutions of an acid and base react together under standard conditions the standard enthalpy change of neutralization is the enthalpy change of that solution.
The enthalpy of neutralization is measured per one mole of water formed. There is heat released when an acid and base react together, hence the enthalpy of neutralization is always negative. Hence, the neutralization reaction is exothermic.
When weak acids or weak bases are involved in a neutralization reaction, their enthalpy of neutralization varies with strong acids or strong bases. Because weak acid is not completely ionized.
Hydration energy of an element means the energy released when it forms a strong covalent bond with water molecules during hydration reaction. The hydration energy of fluoride ions is more than all ions in halogen groups because the energy required to break the F-F bond is less and hence hydration energy more.
For example, consider the below neutralization reaction between HF (weak acid) and NaOH (Strong base),
$HF+NaOH\to NaF+H_{2}O$
Although HF is a weak acid, then the enthalpy of neutralization is very high. i.e, greater than 57.3kJ/mol.

Hence, the correct answer is option (B).

Note: For reactions involving strong acid and strong base, the enthalpy of neutralization values between 57 kJ/mol and 58 kJ/mole. Strong acid and strong base are completely ionized during neutralization in an aqueous solution.