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The heat of formation of crystalline sod...

The heat of formation of crystalline sodium chloride is `-410 kJ mol^(-1)`. The heat of sublimation of sodium metal is `180.8 kJ mol^(-1)`. The heat of dissociation of chlorine gas into atoms is `242.7 kJ mol^(-1)`. The ionisation energy of Na and electron affinity of Cl are `493.7 kJ and -368.2 kJ `respectively. Calculate the lattice energy of NaCl. 

Text Solution

Verified by Experts

Based on the Hess law , Born-Haber cycle is constructed. `Q+S +(1)/(2) D +I -E -U`
Substituting the respective values, we get
`-410 =108.8 + (1)/(2) xx 242.7 + 493.7 - 368.2 +U`
Lattice energy of sodium chloride,
`U=- 765.65kJ mol ^(-1).`
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