Question

Given that diatomic chlorine gas is the stablest form of the element, and that the Hf° value for atomic chlorine is 121.7 kJ mol 1, calculate the maximum wavelength of light that can dissociate diatomic chlorine into the monatomic form. Does such a wavelength correspond to light in the visible or the UV-A or the UV-B region?

Answer 1

Answer – We are given the, ∆Hf^o = 121.7 kJ/mol for the atomic chlorine

We know,

∆Hf^o in kJ = 121.7 kJ/mol* 1 mole / 6.023*10²³

                = 2.02*10^-22 kJ

               = 2.02*10^-19 J

We know, E = h*C/λ

So, λ = h*C / E

        = 6.626*10^-34 J.s * 3.0*10⁸ m.s^-1 / 2.02*10^-19 J

        = 9.84*10^-7 m

      = 984 nm

maximum wavelength of light that can dissociate diatomic chlorine into the monatomic form is 984 nm

The visible light wavelength range is 400 nm to 780 nm and for UV it is 200 to 400 nm, so this wavelength is not corresponding to light in the visible or the UV-A or the UV-B region.