The electron affinity of a hypothetical element `'A'` is `3eV` per atom. How much energy in kcal is released when `10g` of `'A'` is completely converted of `A^(-)` ion in a gaseous state ?
`(1 eV=23" kcal mol"^(-1)`, Molar mass of `A=30g)`

Answer

23

Explanation

`A +e^(-) rarr A^(-)+ 3ev`
Number of mole of `A = 10//30`.
As 1 mole of `A` releases the amount of energy `= 3 xx 23 kcal`.
`:.` Energy released for conversion of 10//30 mole of gaseous `A` into `A^(-)` ions `= (3 xx 23)/(30) xx 10 = 23 kCa`l