Question

Calculate the wavelength of light required to break the bond between two chlorine atoms in a chlorine molecule. The Cl - Cl bond energy is 243 kJ $mo{l}^{-1}(h=6.6\times 10^{-34}Js;c=3\times 10^{8}m/s$ ; Avogadro’s number $=6.02\times 10^{23}mo{l}^{-1}$ )

• A. $8.18\times 10^{-31}m$
• B. $6.26\times 10^{-21}m$
• C. $4.905\times 10^{-7}m$
• D. $4.1\times 10^{-6}m$

Answer 1

Answer: (C)

Energy required to break one Cl − Cl bond $=\frac{bondenergypermole}{Avogadro’snumber}=\frac{243\times 10^3}{6.02\times 10^{23}}J$

Let the wavelength of the photon to cause rupture of one Cl - Cl bond be λ,

$\lambda =\frac{hc}{E}=\frac{6.6\times 10^{-34}\times 3\times 10^8\times 6.02\times 10^{23}}{243\times 10^3}=\frac{119.196}{243}\times 10^{-34}\times 10^{31}\times 10^{-3}=4.905\times 10^{-7}m.$