The heat of formation of `PCl_(5)(s)` from the following data will be : `2P(s)+3Cl_(2)(g)to 2PCl_(3)(l), Delta H = - 151.8` Kcal and `PCl_(3)(l)+Cl_(2)(g)to PCl_(5)(s) , Delta H =- 32.8` Kcal

Options

A. `-108.7` kcal
B. `+108.7` kcal
C. `-184.6` kcal
D. `+` 184.6 kcal

Answer

A

Explanation

(i) `2P(s) + 3Cl_(2)(g) rarr 2PCl_(3) (l), Delta H= -1518`kcal
(ii) `PCl_(3)(l) + Cl_(2)(g) rarr PCl_(5)(s), Delta H= -32.8` kcal
`(1)/(2) xx Eq (i) + Eq (ii)`
`P(s) + (5)/(2) Cl_(2)(g) rarr PCl_(5)(s), Delta H= (1)/(2) (-151.8) - 328 Delta H= -108.7` kcal