Question
The absolute enthalpy of neutralisation of the reaction
$$MgO\left( s \right) + 2HCl\left( {aq} \right) \to $$ $$MgC{l_2}\left( {aq} \right) + {H_2}O\left( l \right)$$
will be
A.
$${\text{less than}}\, - 57.33\,kJ\,mo{l^{ - 1}}$$
B.
$$ - 57.33\,kJ\,mo{l^{ - 1}}$$
C.
$${\text{greater than}}\, - 57.33\,kJ\,mo{l^{ - 1}}$$
D.
$$57.33\,kJ\,mo{l^{ - 1}}$$
Answer :
$${\text{less than}}\, - 57.33\,kJ\,mo{l^{ - 1}}$$
Solution :
Heat of neutralisation of strong acid and strong base is $$ - 57.33\,kJ.$$ $$MgO$$ is weak base while $$HCl$$ is strong acid, so the heat of neutralisation of $$MgO$$ and $$HCl$$ is lower than $$ - 57.33\,kJ$$ because $$MgO$$ requires some heat for ionisation, therefore the net released amount of heat is decreased.