JEE Advance - Chemistry (1995 - No. 4)
Iodine molecule dissociates into atoms after absorbing light of 4500 Å. 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)
4.3 x 10^-20 J
2.15 x 10^-20 J
8.6 x 10^-20 J
4.41 x 10^-19 J
3.98 x 10^-19 J
Explanation
Bond energy per molecule $$ = {{240 \times {{10}^3}\,J} \over {6.02 \times {{10}^{23}}}}$$
$$ = 3.98 \times {10^{ - 19}}$$ J/molecule
Energy absorbed
$$hc/\lambda = {{6.62 \times {{10}^{ - 34}}\,Js \times 3 \times {{10}^8}\,m\,{s^{ - 1}}} \over {4500 \times {{10}^{ - 10}}\,m}}$$
$$ = 4.41 \times {10^{ - 19}}\,J$$
Kinetic energy
$$ = (4.41 \times {10^{ - 19}} - 3.98 \times {10^{ - 19}})\,J$$
$$ = 4.3 \times {10^{ - 20}}\,J$$
Kinetic energy per atom
$$ = {{4.3 \times {{10}^{ - 20}}} \over 2}\,J = 2.15 \times {10^{ - 20}}\,J$$