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Question

Given that bond energies of HH and ClCl are 430 kJ mol1 and 240 kJ mol1 respectively and ΔfH for HCl is 90 kJ mol1. Bond enthalpy of HCl is :

A
245 kJ mol1
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B
290 kJ mol1
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C
380 kJ mol1
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D
425 kJ mol1
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Solution

The correct option is C 425 kJ mol1
Given :

Bond energies of HH and ClCl bonds which can be represented as follows :

H2(g)2H(g)ΔH(H)=+430kJmol1

Cl2(g)2Cl(g)ΔH(Cl)=+240kJmol1

HCl(g)H(g)+Cl(g)ΔH(Hcl)=?

12H2+12Cl2HCl

ΔfHHCl=ΔHBEReactant+ΔHBEProductBE of HCl

90=12×430+12×240BE of HCl

BE of HCl=215+120+90=305+120=425kJmol1

Where, BE= Bond enthalpy

Hence, the correct option is D.

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