Calculate the lattice energy of sodium chloride crystal from the following data: Born exponent, n=8, Madelung constant for NaCl=1.748, Ionic radius of `Na^(+)=0.95 Å`, Ionic radius of `Cl^(-)=1.81Å`.

Explanation

`r_0 = 0.95 Å + 1.81Å = 2.76Å = 2.76. 10^(-10) m`
According to Born lange.s equation, lattice enthalpy, `Delta_("lattice") H = 1.39 xx 10^5 (Z^+ Z^- A)/(r_0) (1 - 1/n)`
` = 1.39 xx 10^5 Nm^2 "mol"^(-1) (1 xx 1 xx 1.748)/(2.76 xx 10^(-10)m) (1-1/8) = -770kJ "mol"^(-1)`