Question

Bond dissociation energy of XY,X2, and Y2 (all diatomic molecules) are in the ratio of 1:1:0.5 and ΔHf of XY is −100 kJ mol−1. The bond dissociation energy of X2 is 100x. The value of x is

Answer 1

Explanation:
Given:Bond dissociation energy of XY,X2 and Y2 are in the ratio 1:1:0.5ΔHf of XY=−100 kJ mol−1Let the bond dissociation energy for XY be 'a'.Therefore, for X2 it is 'a' and for Y2 it is a2Now,12X2+12Y2→XY;ΔHf=−100kJmol−1One X−X and one Y−Y are broken and one X−Y is formed:∴12a+12(a2)−a=−100kJmol−1⇒a2+a4−a=−100⇒2a+a−4a4=−100⇒a=−400∴a=400Here, 'a' is the bond dissociation energy of X2=100x100x=400x=4Hence, the correct answer is 4.