Question

Iodine molecule dissociates into atoms after absorbing light of 4500 $\stackrel{o}{A}$ . If one quantum of radiation is absorbed by each molecule. Calculate the kinetic energy of iodine atoms (bond energy of $I_2=240kJmo{l}^{-1}$)

• A. $0.216\times {10}^{-18}J$
• B. $0.216\times {10}^{-19}J$
• C. $0.216\times {10}^{-17}J$
• D. $0.216\times {10}^{-20}J$

Answer 1

The correct option is B $0.216\times {10}^{-19}J$

Energy given to $I_2$ molecule $=\frac{hc}{\lambda }$
$=\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{4500\times {10}^{-10}}=4.417\times {10}^{-19}J$
Energy used for breaking up $I_2$ molecules
$=\frac{240\times {10}^3}{6.023\times {10}^{23}}=3.984\times {10}^{-19}J$
$\therefore$ Energy used in imparting K.E to two I atoms
$(4.417\times {10}^{-19}-3.984\times {10}^{-19})J=0.433\times {10}^{-19}$
K.E per atom $=0.216\times {10}^{-19}J$