MCQ
The energy required to break one mole of $Cl- Cl$ bonds in $Cl_2$ is $242\, kJ \,mol^{- 1}.$ The longest wavelength of light capable of breaking a single $Cl - Cl$ bond is ............ $\mathrm{nm}$

$(C= 3 \times 10^8 \,ms^{-1}$ and $N_A =6.02 \times mol^{-1}).$

  • A
    $594$
  • B
    $640$
  • C
    $700$
  • $494$

Answer

Correct option: D.
$494$
d
Energy required to break one $\mathrm{Cl}_{2}$ molecule $=\frac{242 \times 10^{3}}{6.02 \times 10^{23}} \mathrm{\,J}$

As $\mathrm{E}=\frac{h c}{\lambda}$

So $\lambda=\frac{h c}{E}$

$=\frac{6.626 \times 10^{-34} \times 3 \times 10^{8} \times 6.02 \times 10^{23}}{242 \times 10^{3}}$

$=494 \times 10^{-9} \mathrm{\,m}$

$=494 \mathrm{\,nm}$

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