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Question

Iodine molecule dissociates into atoms after absorbing light of $$4500 \mathring{A}$$. If one quantum of radiation is absorbed by each molecule, calculate the kinetic energy of iodine atoms 
[Bond energy of $$I_2 = 240\ kJ\ mol^{-I}$$].


A
216×1020kJ
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B
2.16×1019J
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C
0.108×1019J
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D
0.216×1019J
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Solution

The correct option is C $$0.216\times 10^{-19}J$$
Energy given to $$I_2$$ molecule $$=\displaystyle\frac{hc}{\lambda}=\displaystyle\frac{6.626\times 10^{-34}\times 3.0\times 10^8}{4500\times 10^{-10}}$$$$=4.417\times 10^{-19}J$$
Also, energy used for breaking up of $$I_2$$ molecule is $$\cfrac{B.E}{N_A}=\displaystyle\frac{240\times 10^3}{6.023\times 10^{23}}=3.984\times 10^{-19}J$$

$$\therefore$$ Energy used in imparting kinetic energy to two $$I$$ atoms $$=(4.417-3.984)\times 10^{-19}J$$

$$\therefore$$ KE/iodine atom $$\dfrac{(4.417-3.984)}{2} \times 10^{-19}$$ $$=0.216\times 10^{-19}J$$

Hence, the correct option is $$D$$

Chemistry

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