Question

The absolute enthalpy of neutralisation of the reaction $MgO (s)+2 HCl (a q) \longrightarrow MgCl _{2}(a q)+ H _{2} O (l)$ will be

• A. less than $-57.33 \,kJ \,mol ^{-1}$
• B. $-57.33 \,kJ \,mol ^{-1}$
• C. greater than $-57.33\, kJ\, mol ^{-1}$
• D. $57.33\, kJ\, mol ^{-1}$

Answer 1

Answer: (A)

less than $-57.33 \,kJ \,mol ^{-1}$

Answer 2

Heat of neutralisation of strong acid and strong base is $-57.33\, kJ . MgO$ is weak base while $HCI$ is strong acid, so the heat of neutralisation of $MgO$ and $HCI$ is lower to $-57.33\, kJ$ because $MgO$ requires some heat in ionisation, then net released amount of heat is decreased.