Q. The average energy required to break a $P - P$ bond in $P _{4}$ (s) into gaseous atoms is $53.2\,kcal\, mol ^{-1}$. The bond dissociation energy of $H _{2}( g )$ is $104.2 \,kcal\, mol ^{-1} ; \Delta H _{ f }^{0}$ of $PH _{3}( g )$ from $P _{4}( s )$ is $5.5 \,kcal \,mol ^{-1}$. The $P - H$ bond energy in $kcal \,mol ^{-1}$ is [Neglect presence of van der Waals forces in $P _{4}( s )$ ]
Thermodynamics
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