ThermochemistryHard

Question

AB, A2 and B2 are diatomic molcules. If the bond enthalpies of A2 AB and B2 are in the ratio 1 : 1 :0.5 and enthalpy of formation of AB from A2 and B2 is - 100kJ mol-1. What is the bond energy of A2

Options

A.200 kJ mol-1
B.100 kJ mol-1
C.300 kJ mol-1
D.400 kJ mol-1

Solution

Let bond energy of A2 be x than bond energy of AB is also x and bond energy of B2 is x/2.
Enthalpy of formation of AB is - 100 kJ/mole : A2 + B2 → 2AB
A2 + B2 → 2AB; ᐃH = - 100kJ
or - 100 = - x
∴ - 100 = ∴ x = 400 kJ

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