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

`{:(XY rarr X_((g))+Y_((g))," "Delta H =+" a kJ/mole ...(i)"),(X_(2) rarr 2X, " "Delta H= +" a kj/mole ...(ii)"),(Y_(2) rarr 2Y," "Delta H =+0.5a" kJ/ mole ...(iii)"):}`
`(1)/(2) xx (ii) +(1)/(2) xx (iii) -(i),` gives
`(1)/(2) X_(2) +(1)/(2) Y_(2) rarr XY`,
`Delta H =(+(a)/(2)+(0.5)/(2) a-a)" kJ/mole "+(a)/(2) +(0.5a)/(2)-a=-200`
`a=800`