Question

$HF\left(aq\right)+NaOH\to NaF\left(aq\right)+H_{2}O\left(l\right)\Delta H=-68.6kJ/mol$ The high negative value of heat of reaction is due to:

• A. In aqueous solution, $HF$ is strong acid
• B. Due to the high hydration energy of $F^{-}$ ion
• C. Heat of neutralisation of any strong acid with $NaOH$ is $-68.6{\text{kJ mol}}^{-1}$
• D. $HF$ is an associated liquid

Answer 1

The correct option is B Due to the high hydration energy of $F^{-}$ ion

a) $HF$ is not a strong acid, since it is not completely dissociated in water.
b) Since $F^{-}$ is very small, hydration of $F^{-}$ releases a lot of energy. Thus the reaction is highly exothermic.
c) Generally, strong acids reacts with strong bases to give almost similar heat of neutralisation value.
d) $HF$ is an associated liquid but it is not the reason for the high negative value of heat of the reaction