The bond dissociation energies of `X_2, Y_2 and XY` are in the ratio of `1 : 0.5 : 1. DeltaH` for the formation of XY is -200 kJ mol^(-1)`. The bond dissociation energy of `X_2` will be

Options

A. `400 kJ mol^(-1)`
B. `300 kJ mol^(-1)`
C. `20 kJ mol^(-1)`
D. None of these

Answer

D

Explanation

Formation of XY is known as : `1/2 X_(2) + 1/2 Y_(2) to XY`
`Delta H = (BE)_(x-x) + (BE)_(Y-Y) - 2(BE)_(X-Y)`
If `(BE)` of `X - Y = a`
Then `(BE)` of `(X -X) = a`
and `(BE) "of" (Y - Y) = a/2`
`:. " "Delta H_(f) (X- Y) = -200 kJ " " :. " " -400 ("for" 2 mol XY) = a + a/2 - 2a`
`implies - 400 = -a/2 implies a = +800 kJ`.