Question

When a mole of crystalline sodium chloride is prepared, `410 kJ` of heat is produced. The heat of sublimation of sodium metal is `180.8kJ`. The heat of dissociation fo chloride gas into atoms is `242.7kJ`. The ionisation energy of `Na` and electron affinity of `CI` are `493.kJ` and `-368.2 kJ`, respectively. calculate the lattice enegry of `NaCI`.

Answer 1

Applying the equation
`-Q = Delta_("sub")H^(Theta) +(1)/(2)D-IP -EA +U`
and substituting the respective values.
`=- 410 = 108.8 +(1)/(2) xx 242.7 +493.7 - 368.2 +U`
`rArr U =- 775.65 kJ mol^(-1)`