Question

The heat of neutralisation becomes large if either the acid or the base is weak.If true enter 1 else o

• A. 0

Answer 1

The correct option is A 0
The magnitude of enthalpy of neutralization of a weak acid is smaller than that of a strong acid.
For example the heat of neutralization of HCl (a strong acid) is -13.7 kcal/mole whereas the heat of neutralization of HCN (a weak acid) is -2.9 kcal/mol as 10.8 kcal/mol of heat is absorbed for the ionisation of
HCN.
$HCl\left(aq\right)+NaOH\left(aq\right)\to NaCl\left(aq\right)+H_{2}O\Delta H=-13.7kcal$
$HCN\left(aq\right)+NaOH\left(aq\right)\to NaCN\left(aq\right)+H_{2}O\Delta H=-2.9kcal$
$HCN\left(aq\right)\rightleftharpoons H^{+}+C{N}^{-}\Delta H10.8kcal$
Thus, the heat of neutralisation becomes smaller if either the acid or the base is weak.