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Question

The dissociation energy of H2 is 430.53 kJ/mol. If H2 is exposed to a radiation of wavelength of 253.7 nm, what percent of radiant energy will be converted into kinetic energy?

A
5.69%
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B
13.59%
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C
8.46%
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D
18.56%
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Solution

The correct option is C 8.46%
Dissociation energy per 1 mol is given as 430.53 kJ/mol which implies that for NA molecules the dissociation energy is 430.53 kJ/mol.

Hence, the dissociation energy for 1 molecule of H2 = 430.53×1036.023×1023 = 7.14×1019 J/molecule

According to Planck's constant, E = hcλ
where, h = Planck's constant
c = Speed of light
λ = Wavelength of radiant energy

Total energy E = 6.626×1034×3×108253.7×109 = 7.8×1019 J

7.14×1019 J energy is absorbed by 1 molecule of H2 to dissociate

So Energy converted into KE = 7.8×1019J7.14×1019 J
= 0.66×1019 J

% energy converted to kinetic energy = 0.66×10197.8×1019×100 = 8.46%

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