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. ` 400 kJ mol^(-1)`
D. ` 800 kJmol^(-1)`

Answer

D

Explanation

Suppose bond dissociation energy of XY `=akJ mol^(-1) , i.e., `BE ( XY )= a . Then BE `9X_(2)0= a, BE(Y_(2))= 0.5 a`
Aim `: (1)/(2) X_(2)+ (1)/(2) Y_(2) rarr XY`
`Delta_(r)H = BE` ( Reactants ) - BE ( Products )
`= [ (1)/(2) BE (X_(2)) + (1)/(2) BE(Y_(2)) ] = BE(XY)`
`:. - 200 = ((a)/(2) + (0.5a)/( 2)) -a`
or ` - 200 = - 0.25 a` or `a= 800 kJ mol^(-1)`