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: (C)

The absolute value of enthalpy of neutralization of this reaction is greater than $-57.33 kJ mol ^{-1}$.

This is due to the very high enthalpy of hydration of $Mg ^{2+}$ ion. The change in enthalpy of this reaction is nearly $-146 kJ$.

Thus enthalpy of neutralization per mole of $H ^{+}$ion is nearly $-73 kJ$, which is greater than the enthalpy of neutralization strong acid against strong base i.e. $-57.33 kJ$.