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Calculate the heat of formation of PCl(5...

Calculate the heat of formation of `PCl_(5)(s)` from the following data :
`2P(s) + 3Cl_(2)(g) rarr 2PCl_(3)(l) Delta H = -151.8 kcal`
`PCl_(3)(l) + Cl_(2)(g) rarr PCl_(5)(s) Delta H = -32.8 kcal`

A

`-108.7 kcal`

B

108.7 kcal

C

`-184.6 kcal`

D

184.6 kcal

Text Solution

Verified by Experts

The correct Answer is:
A
(i) `2P(s) + 3Cl_(2)(g) rarr 2PCl_(3)(l) Delta H = - 151.8 kcal`
(ii) `PCl_(3)(l) + Cl_(2)(g) rarr PCl_(5)(m) Delta H = - 32.8 kcal`
`P(s) + (5)/(2) Cl_(2)(g) rarr PCl_(5)(s) Delta H = ?`
Dividing equation (i) by 2 and add equation (ii)
`P(s) + (5)/(2) Cl_(2)(g) rarr PCl_(5)(s) Delta H = -75.9 - 32.8 = -108.7 kcal`
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