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

Answer:

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

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

$E = \frac{242800 J}{6.022\times 10^{23}}=4.032\times 10^{-19} J$

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

$E=\frac{hc}{\lambda }$

$\lambda =\frac{hc}{E}$

$=\frac{6.626\times 10^{-34} Js\times 3\times 10^8 m/s}{4.032\times 10^{-19} J}$

$\lambda = 4.930\times 10^{-7} m = 493.02 nm$

$1 m = 10^09 nm$

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