question_answer

The heat of atomization of \[P{{H}_{3}}(g)\] is \[228\text{ }kcal\text{ }mo{{l}^{-1}}\] and that of \[{{P}_{2}}{{H}_{4}}(g)\] is\[335\text{ }kcal\text{ }mo{{l}^{-1}}\]. The energy of the P-P bond is

A) \[102\text{ }kcal\text{ }mo{{l}^{-1}}\]             

B) \[51\text{ }kcal\text{ }mo{{l}^{-1}}\]

C) \[26\text{ }kcal\text{ }mo{{l}^{-1}}\]               

D) \[204\text{ }kcal\text{ }mo{{l}^{-1}}\]

Correct Answer: B

Solution :

[b] Bond dissociation energy of \[P{{H}_{3}}\left( g \right)=228\text{ }kcal\text{ }mo{{l}^{-1}}\] \[P-H\] bond energy\[=\frac{228}{3}=76\text{ }kcal\text{ }mo{{l}^{-1}}\] Bond energy of \[4(P-H)+(P-P)\] \[=355\text{ }kcal\text{ }mo{{l}^{-1}}\] or \[4\times 76+\left( P-P \right)=355\text{ }kcal\text{ }mo{{l}^{-1}}\] \[=P-P\] bond energy \[=51\text{ }kcal\text{ }mo{{l}^{-1}}\]