One moles of anhydrous `AB` dissolves in water and liberates `21.0 J mol^(-1)` of heat. The valueof `DeltaH^(Theta)` (hydration) of `AB` is `-29.4 J mol^(-1)`. The heat of dissolution of hydrated salt `AB.2H_(2)O(s)` is

Options

A. `50.4 J mol^(-1)`
B. `8.4 J mol^(-1)`
C. `-50.4 J mol^(-1)`
D. `-8.4 J mol^(-1)`

Explanation

Dissolution of anhydrous salt `AB`
`AB +aq +2H_(2)O rarr AB. 2H_(2)O (aq),DeltaH^(Theta) =- 21.0 J mol^(-1) ..(1)`
Hydration of `AB` salt
`AB +2H_(2)O rarr AB.2H_(2)O(s),DeltaH^(Theta) =- 29.4J mol^(-1) …(2)`
Substracting equation (2) from (1) we get
`AB.2H_(2)O(s)+aq rarr AB.2H_(2)O(aq),DeltaH^(Theta) = 8.4J mol^(-1)`