Question

Iodine molecule dissociates into atoms after absorbing light of $4500 \AA$ If one quantum of radiation is absorbed by each molecule, calculate the kinetic energy of iodine atoms. (Bond energy of I2 = 240 kJ $mol^{-1}$)

Answer 1

Given, Bond energy of$I_2 = 240KJmol^{-1}$, λ = 4500A°  

Energy given to Iodine $I_2$ molecule = hc/λ

                                                                 = $\frac{6.626\times 10^{-34}\times 3\times10^8}{4500\times10^{-10}}$

= $4.417\times 10^{-19} J$

Energy used for breaking up of Iodine $I_2$ molecule =  $\frac {2.4\times 10^{3}}{6.023\times 10^{23}}$

= $3.984\times10^{-19} J$

Energy used in importing kinetic energy to two I atoms =$[4.417-3.984]\times10^{-19} J$

So, Kinetic energy per Iodine atom = $\frac{(4.417-3.984)}{2}\times10^{-19} J = 0.216\times10^{-19} J$