Question

If the bond dissociation energies of XY, X₂ and Y₂ (all diatomic molecules) are in the ratio of 1 : 1 : 0.5 and ΔHf for the formation of XY is – 200 KJ mol^–1. The bond dissociation energy of X₂ will be

(A)   100 KJ mol^–1

(B)   200 KJ mol^–1

(C)   300 KJ mol^–1

(D)   800 KJ mol^–1

Answer 1

Correct option  (D) 800 KJ mol^–1

Explanation:

Let the bond dissociation energy of XY, X₂ and Y₂ be x,x and x, KJ/mol respectively,  1/2X₂  + 1/2 XY; ΔHf = – 200 KJ mol^–1.  ΔHreaction = [(sum of bond dissociation energy of all reactants) – (sum of bond dissociation energy of product)]

Second method