Question

Calculate $\Delta H _{ f }$ (in kcal) for the formation of $MgS$ from the Born-Haber cycle given below

All the values are in $kcal / mol . \Delta H _{ f }$ is the enthalpy of formation of $MgS ( s ) . IP _{ I }$ and I.P $_{ II }$ are first and second I.E. Given 3(I.P $_{1}+$ I.P $_{ II }$ ) $=-19 \Delta H _{ f }$

Answer 1

For Born - Harber cycle of $Mgs$
$\Delta H _{ f }=133.2+\left(-\frac{19}{3} \Delta H _{ f }\right)+\frac{36.5}{8}-72.4-700.2$
$\therefore \Delta H _{ f }=-86.6\, kcal$