Chemical Thermodynamics Question 344
Question: The heat of atomization of methane and ethane are $ 360kJ/mol $ and $ 620kJ/mol $ , respectively. The longest wavelength of light capable of breaking the $ C-C $ bond is (Avogadro number $ =6.02\times 10^{23}mo{{l}^{-1}},h=6.62\times {{10}^{-34}}Js): $
Options:
A) $ 2.48\times 10^{4}nm $
B) $ 1.49\times 10^{3}nm $
C) $ 2.48\times 10^{3}nm $
D) $ 1.49\times 10^{4}nm $
Show Answer
Answer:
Correct Answer: B
Solution:
In $ CH_4,4\times B{E_{(C-H)}}=360kJ/mol $
$ \therefore B{E_{(C-H)}}=90kJ/mol $ In $ C_2H_6,B{E_{(C-C)}}+6\times B{E_{(c-H)}}=620kJ/mol $
$ \therefore B{E_{(C-C)}}=80KJ/mol $
$ \therefore B{E_{(C-C)}}=\frac{80\times 10^{3}}{6.023\times 10^{23}}J/molecule $ Now, $ E=\frac{hc}{\lambda } $
$ \therefore \lambda =\frac{6.626\times {{10}^{-34}}\times 3\times 10^{8}\times 6.023\times 10^{23}}{80\times 10^{3}} $
$ \therefore \lambda =1.49\times 10^{3}nm $
