Enthalpy of Neutralization of Strong Acid and Strong Base - Practice Questions & MCQ

Heat of Neutralization

It is enthalpy change during neutralization of 1 equivalent of an acid and base.

Case of Strong Acid and Strong Base:

$\mathrm{HCl}+\mathrm{NaOH} \longrightarrow \mathrm{NaCl}+\mathrm{H}_2 \mathrm{O}$

The enthalpy change of the above reaction is equal to -13.7 kcal eq^-1 or -57.3 kJ eq^-1.

It is to be noted that the enthalpy of neutralisation of 1 equivalent of any strong acid or strong base is equal to  -13.7 kcal eq^-1 or -57.3 kJ eq^-1.

$\mathrm{H}^{+}+\mathrm{OH}^{-} \longrightarrow \mathrm{H}_2 \mathrm{O}, \Delta \mathrm{H}=-13.7 \mathrm{kcal} \mathrm{mol}^{-}$

Case in which any one of the Acid or Base (or Both) are weak:

In case one of the acid or base is weak, then some part of the heat will be used up for ionisation of the weak component and the heat liberated will be lesser than the above values

For example

$\mathrm{CH}_3 \mathrm{COOH}+\mathrm{NaOH} \longrightarrow \mathrm{CH}_3 \mathrm{COONa}+\mathrm{H}_2 \mathrm{O},|\Delta \mathrm{H}|<13.7 \mathrm{kcal} \mathrm{eq}^{-1}$

Properties of enthalpy of neutralisation:

• It is always exothermic $\Delta \mathrm{H}=-\mathrm{ve}$
• The heat of neutralization of strong acid and strong base is always 13.7 Kcal/mole or 57 kJ/mole.
• It is independent of the nature of strong acid or strong base.
• If one electrolyte is weak then $\Delta \mathrm{H}$ will be less than —13.7 Kcal as some amount of heat will be absorbed in ionisation of the weak electrolyte.
• In the case of HF, $\Delta \mathrm{H}$ is more due to more hydration of F^- ions.