If the bond dissociation energies of XY, , X_2 and Y_2 (all diatomic molecules) are in the ratio of 1 : 1 : 0.5 and _f H for the formation of XY is - 200 ,kJ ,mol e^ - 1 . The bond dissociation energy of X_2 will be.....kJ ,mo l^ - 1

If the bond dissociation energies of XY, , X_2 and Y_2 (all diato…

MCQ

If the bond dissociation energies of $XY,\,{X_2}$ and ${Y_2}$ (all diatomic molecules) are in the ratio of $1 : 1 : 0.5 $ and ${\Delta _f}H$ for the formation of $XY$ is $ - 200\,kJ\,mol{e^{ - 1}}$. The bond dissociation energy of ${X_2}$ will be.....$kJ\,mo{l^{ - 1}}$

A
$100$
✓
$800$
C
$300$
D
$400$

✓

Answer

Correct option: B.

$800$

(b)$XY\xrightarrow{{}}{X_{(g)}} + {Y_{(g)}}$ $\Delta H = + a\,\,kJ/mole$ ……….$(i)$

${X_2}\xrightarrow{{}}2X$; $\Delta H = + a\,\,kJ/mole$ ………. $(ii)$

${Y_2}\xrightarrow{{}}2Y$; $\Delta H = + 0.5\,a\,\,kJ/mole$ ……….$(iii)$

$\frac{1}{2} \times {\text{(ii) }} + \frac{{\text{1}}}{{\text{2}}} \times {\text{(iii) - (i),}}$ gives

$\Delta H = \left( { + \frac{a}{2} + \frac{{0.5}}{2}a - a} \right)\,\,kJ/mole$
$ + \frac{a}{2} + \frac{{0.5a}}{2} - a = - 200$
$a = 800$

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