The heat of atomization of methane and ethane are 360kJ/mol and 620kJ/mol, respectively the longest wavelength light capable of breaking the C−C bond is (Avodrago constant =6.02×1023mol−1). 

The heat of atomization of methane and ethane are 360kJ/mol and 620kJ/mol, respectively the longest wavelength light capable of breaking the CC bond is (Avodrago constant =6.02×1023mol1). 

  1. A

    1.49×103nm

  2. B

    2.48×103nm

  3. C

    2.48×104nm

  4. D

    1.49×104nm

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    Solution:

    Given data as

    CH4(g)C(g)+4H(g)    ΔH1=4εCHC2H6(g)2C(g)+6H(g)    ΔH2=εCC+6εCH

    From  ΔH1, we get   εCH=(360/4)kJmol1=90kJmol1

    From  ΔH2, we get   εCH=ΔH26εCH=(6206×90)kJ1=80kJmol1

    For a single C-H  bond, we have

    E=εCHNA=80kJmol16.02×1023mol1=1.33×1022kJ=1.33×1014J

    The longest wavelength required to break this bond is

    λ=hcE=6.626×1034Js3×108ms11.33×1019J=1.495×106m=1.495×103nm

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