Question

Calculate the wavelength of the radiation that would cause photo dissociation of chlorine molecule if the $Cl-Cl$ bond energy is $240\text{kJ/mol}$.
(take Avogadro's number to be $6\times {10}^{23}$, and Planck's constant (h) = $6.6\times {10}^{-34}\text{J s}$)

• A. $8.72\times {10}^{-7}\text{m}$
• B. $9.25\times {10}^{-10}\text{m}$
• C. $10.42\times {10}^{-22}\text{m}$
• D. $4.95\times {10}^{-7}\text{m}$

Answer 1

The correct option is D $4.95\times {10}^{-7}\text{m}$

Bond Energy of one mole of $C{l}_2=240\text{kJ/mol}$
Bond energy per molecule of $C{l}_2$ $=\frac{\text{energy for one mole in joules}}{\text{Avogadro's number}}$
$\text{Energy per molecule}=\frac{240000}{6\times {10}^{23}}=40\times {10}^{-20}$

Wavelength of radiation,
$E=\frac{hc}{\lambda }$
$40\times {10}^{-20}=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{\lambda }$
$\lambda =4.95\times {10}^{-7}\text{m}$