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BCECE Engineering BCECE Engineering Solved Paper-2004

  • question_answer
    For\[A\xrightarrow{{}}B,\Delta H=4\,k\,cal\,mo{{l}^{-1}}\] \[\Delta S=10\,cal\,mo{{l}^{-1}}{{K}^{-1}}\]reaction is spontaneous when temperature can be:

    A) 400 K                    

    B)        300 K    

    C)        500 K                    

    D)        none of these

    Correct Answer: C

    Solution :

    Key Idea: The reaction is spontaneous when value of \[\Delta G\] is negative. Given  \[\Delta S=10\,cal\,mo{{l}^{-1}}{{K}^{-1}}\]                 \[\Delta H=4\,kcal\,mo{{l}^{-1}}=4000\,cal\,mo{{l}^{-1}}\]                 Let          \[\Delta G=0\]                                 \[\Delta G=\Delta H-T\Delta S\]                                 \[0=4000-T\times 10\]                 or            \[T=\frac{4000}{10}=400\,K\] \[\therefore \]Reaction is spontaneous at temperature above 400 K The only choice having temperature above \[=400K\]is\[(c)\,500K\] \[\therefore \](c) is correct answer


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