Browse Questions

# $MgO(s) + 2HCl(aq) \longrightarrow MgCl_2(aq) + H_2O(l)$; The absolute enthalpy of neutralisation of the reaction is

(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: greater than -57.33 kJ $mol^{-1}$
The absolute value of enthalpy of neutralisation of this reaction is greater than -57.33 kJ $mol^{-1}$.
This is due to very high enthalpy of hydration of $Mg^{2+}$ ion. Infact the $\Delta H$ for this reaction is nearly -146 kJ. Thus enthalpy of neutralisation per mole of $H^+$ ion is nearly -73 kJ, which is greater than enthalpy of neutralisation of strong acid Vs strong base i.e., -57.33 kJ.