Question

The wavelength of radiation which would cause the photodissociation of chlorine molecule if the $Cl-Cl$ bond energy is $243kJmo{l}^{-1}$ is (h = $6.6\times {10}^{-34}Js$).

• A. $4900nm$
• B. $49nm$
• C. $4.90nm$
• D. $490nm$

Answer 1

The correct option is D $490nm$

Energy required to break one $Cl-Cl$ bond $=\frac{\text{Bond energy per mole}}{\text{Avogadro's number}}$
$=\frac{243\times {10}^3}{6.023\times {10}^{23}}J$ =
Let the wavelength of the photon to cause dissociation of one $Cl-Cl$ bond be $\lambda$.
We know that,
$\lambda =\frac{hc}{E}=\frac{6.6\times {10}^{-34}\times 3\times {10}^8\times 6.023\times {10}^{23}}{243\times {10}^3}m$
$\lambda$ = $4.90\times {10}^{-7}m=490nm$