Question

Calculate the `EA` of `O` atom to `O^(2-)` ion from the following data:
i. `Delta_(f)H^(ɵ)[MgO(s)] = -600 kJ mol^(-1)`
ii. `Delta_(u)H^(ɵ) [MgO(s)] = -3860 kJ mol^(-1)`
iii. `IE_(1) + IE_(2)` of `Mg(g) = 2170 kJ mol^(-1)`
iv. `Delta_("diss")H^(ɵ)` of `Mg(s) = + 494 kJ mol^(-1)`
v. `Delta_("sub")H^(ɵ)` of `Mg(s) = +150 kJ mol^(-1)`
A. `+693 kJ mol^(-1)`
B. `-693 kJ mol^(-1)`
C. `+69.3 kJ mol^(-1)`
D. `-69.3 kJ mol^(-1)`

Answer 1

Correct Answer - A
Using Born-Haber cycle for `MgO`, calculation of `EA` of `O` atom to `O^(2-)` ion (All values in `kJ mol^(-1)`)

`:. Delta_(f)H^(ɵ) = Delta_("sub")H^(ɵ) + (IE_(1) + IE_(2)) + (1)/(2) Delta_("diss") + (EA_(1) + EA_(2))+Delta_(U)H^(ɵ)`
`-600 = 150 + 2170 + (1)/(2) xx 494 + (EA_(1)+EA_(2)) - 3860`
`:. (EA_(1) +EA_(2)) = + 693 kJ mol^(-1)`