Question

Calculate the lattice energy of a salt $M{X}_{\left(s\right)}$ from the data given below:
Heat of formation of $MX\left(\Delta H\right)=-550\text{kJ/mol}$
Heat of sublimation of $M\left(S\right)=80\text{kJ/mol}$
Heat of dissociation of $X_2\left(D\right)=155\text{kJ/mol}$
Ionization energy of $M\left(I\right)=347\text{kJ/mol}$
Electron affinity of $X\left(E\right)=-343\text{kJ/mol}$

• A. $-838\text{kJ/mol}$
• B. $-938.5\text{kJ/mol}$
• C. $-711.5\text{kJ/mol}$
• D. $-638.5\text{kJ/mol}$

Answer 1

The correct option is C $-711.5\text{kJ/mol}$


$\Delta H_f=S.E+I.E+\frac{DE}{2}-EA-LE$
$-550=80+347+\frac{155}{2}-343-L.E$
L.E = -711.5 kJ/mol
Hence, the option (c) is correct.