Question

Why is the heat evolved in neutralization of HF is highest

• A. Due to low hydration energy of $F^{-}$ ion
• B. Due to high hydration energy of $F^{-}$ion
• C. HF is a strong acid
• D. none of these

Answer 1

Answer: (B)

Due to high hydration energy of $F^{-}$ ion.

Although HF is a weak acid, its enthalpy change of neutralisation is very high, (more negative) $-57.3kJ$

This is due to high hydration energy of $F^{-}$ ion. The size of $F^{-}$ is very small and thus it can form strong bond with water molecule when it is hydrated.