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 $mol^{- 1}\left(\right.h=6.6\times 10^{- 34}Js;c=3\times 10^{8}m/s$ ; Avogadro’s number $=6.02\times 10^{23}mol^{- 1}$ )

• 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 $=\frac{b o n d \, e n e r g y \, p e r \, m o l e}{A v o g a d r o ’ s \, n u m b e r}=\frac{243 \times 1 0^{3}}{6.02 \times 1 0^{23 \, \, }}J$

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

$\lambda =\frac{h c}{E}=\frac{6.6 \times 1 0^{- 34} \times 3 \times 1 0^{8} \times 6.02 \times 1 0^{23}}{243 \times 1 0^{3}}=\frac{119.196}{243}\times 10^{- 34}\times 10^{31}\times 10^{- 3}=4.905\times 10^{- 7 \, }m.$