If the bond dissociation energies of X Y , X 2 and Y 2 (all diatomic molecules) are in the ratio of 1:1:0.5 and Δ t H for the formation of X Y is − 200 kJ mole − 1 . The bond dissociation energy

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If the bond dissociation energies of X Y , X 2 ​ and Y 2 ​ (all diatomic molecules) are in the ratio of 1:1:0.5 and Δ t ​ H for the formation of X Y is − 200 kJ mole − 1 . The bond dissociation energy of X 2 ​ will be

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​ X Y ⟶ X ( g ) ​ + Y ( g ) ​ ; Δ H = + a kJ / mole ………… .. ( i ) X 2 ​ ⟶ 2 X ; Δ H = + a kJ / mole …………… (ii) Y 2 ​ ⟶ 2 Y ; Δ H = + 0.5 a kJ / mole ………… . (iii) 2 1 ​ × (ii) + 2 1 ​ × (iii) − (i), Gives 2 1 ​ X 2 ​ + 2 1 ​ Y 2 ​ ⟶ XY ; Δ H = ( + 2 a ​ + 2 0.5 ​ a − a ) kJ / mole + 2 a ​ + 2 0.5 a ​ − a = − 200 a = 800. ​

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