NEET Chemistry Thermodynamics / रासायनिक उष्मागतिकी Question Bank Self Evaluation Test - Thermodynamics

  • question_answer
    The heat of atomization of methane and ethane are \[360\text{ }kJ/mol\] and\[620\text{ }kJ/mol\], respectively. The longest wavelength of light capable of breaking the \[C-C\] bond is (Avogadro number \[=6.02\times {{10}^{23}}mo{{l}^{-1}},\,\,h=6.62\times {{10}^{-34}}Js):\]

    A) \[2.48\times {{10}^{4}}nm\]    

    B) \[1.49\times {{10}^{3}}nm\]

    C) \[2.48\times {{10}^{3}}nm\]    

    D) \[1.49\times {{10}^{4}}nm\]

    Correct Answer: B

    Solution :

    In \[C{{H}_{4}},4\times B{{E}_{(C-H)}}=360kJ/mol\] \[\therefore B{{E}_{(C-H)}}=90\text{ }kJ/mol\] In \[{{C}_{2}}{{H}_{6}},B{{E}_{(C-C)}}+6\times B{{E}_{(c-H)}}=620kJ/mol\] \[\therefore B{{E}_{(C-C)}}=80KJ/mol\] \[\therefore B{{E}_{(C-C)}}=\frac{80\times {{10}^{3}}}{6.023\times {{10}^{23}}}J/molecule\] Now, \[E=\frac{hc}{\lambda }\] \[\therefore \lambda =\frac{6.626\times {{10}^{-34}}\times 3\times {{10}^{8}}\times 6.023\times {{10}^{23}}}{80\times {{10}^{3}}}\] \[\therefore \lambda =1.49\times {{10}^{3}}nm\]


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