Question

Photochemical dissociation produces a normal oxygen atom and a oxygen atom 2.5 eV more energetic than normal one. Also the average bond energy of $ {{O}_{2}} $ into normal oxygen is 498 kJ $ mo{{l}^{-1}} $ . Determine the longest wavelength required for photochemical decomposition of $ {{O}_{2}} $ .

• A. 126 nm
• B. 175 nm
• C. 190 nm
• D. 205 nm

Answer 1

Answer: (A)

BE of $ {{O}_{2}} $ per molecule $ =\frac{498\times {{10}^{3}}}{6.023\times {{10}^{23}}}J $ $ =826\times {{10}^{-19}}J $ Energy required for photochemical decom-position of one molecule of $ {{O}_{2}}=826\times {{10}^{-19}}J+2.5\times 1.6\times {{10}^{-19}}J $ $ =1.22\times {{10}^{-18}}J $ $ \lambda =\frac{hc}{E}=\frac{6.625\times {{10}^{-34}}\times 3\times {{10}^{8}}}{1.22\times {{10}^{-18}}}=126\,nm $