Question

calculate the wavelength of light required to break the bond between two Cl atoms in Cl2 molecules.(bond energy of Cl-Cl is 243 kJmol^-1)

Answer 1

Solution :

1 KJ /mol = 0.0167 × 10-19 J / molecule

243 KJ /mol = 0.0167 × 243 × 10-19

                        = 4.067 × 10⁻¹⁹ J /molecule.

According to Planck's law,

E = hc / λ

Therefore,

λ  = hc  / E

h - Planck constant = 6.625 × 10⁻³

c - velocity of light = 3 × 10⁸ m/s

     =  (6.625 × 10⁻³ *  3 × 10⁸ m/s ) /  ( 4.067 × 10⁻¹⁹ )

     = 4.887 * 10⁻⁷ m

λ = 488 nm

nm - nanometer = 10⁻⁹ m