If the bond dissociation energies of `XY,X_(2)` and `Y_(2)(` all diatomic molecules `)` are in the ratio `1:1:0.5` and `Delta_(f)H` of `XY` is `-200 kJ mol^(-1)`. The bond dissociation energy of `X_(2)` will be `:`

Options

A. `100 kJ mol^(-1)`
B. `200 kJ mol^(-1)`
C. `800 kJ mol^(-1)`
D. `400 kJ mol^(-1)`

Answer

C

Explanation

`X-X+Y-Yto2X-Y`, `DeltaH=-200xx2kJ`
Let `B.E. "of" X-X=a`
`B.E. "of" X-Y=a`
and `B.E. "of" Y-Y=a//2`
`DeltaH=-400 kJ`
`DeltaH=B.E. (X-X)+B.E.(Y-Y)-2xxBE(X-Y)`
`-400kJ=a+0.5a-2a`
`0.5a=400 kJ`
`a=800 kJ`
`B.E. "of" X_(2)=a=800 kJ mol^(-1)`