Question

A common way of initiating certain chemical reactions with light involves the generation of free halogen atoms in solution. If ΔH for the reaction Cl 2(g) → 2Cl(g) is 242.8 kJ/mol, what is the longest wavelength of light that will produce free chlorine atoms in solution?

Answer 1

493.02 nm is the longest wavelength of light that will produce free chlorine atoms in solution.

Step-by-step explanation:

`Cl_2(g)\rightarrow 2Cl(g)` ,ΔH = 242.8 kJ/mol

Energy required to break 1 mole of Cl-Cl bond = 242.8 kJ

Energy required to break 1 Cl-Cl bond = E

`E = (242800 J)/(6.022* 10^(23))=4.032* 10^(-19) J`

Energy related with the wavelength of light is given by Planck's equation:

`E=(hc)/(\lambda )`

`\lambda =(hc)/(E)`

`=(6.626* 10^(-34) Js* 3* 10^8 m/s)/(4.032* 10^(-19) J)`

`\lambda = 4.930* 10^(-7) m = 493.02 nm`

`1 m = 10^09 nm`

493.02 nm is the longest wavelength of light that will produce free chlorine atoms in solution.