JCECE Engineering JCECE Engineering Solved Paper-2014

  • question_answer
    The half-life period for first order reaction having activation energy \[39.3\,\,kcal\,\,mo{{l}^{-1}}\] at \[{{300}^{o}}C\] and frequency constant \[1.11\times {{10}^{11}}{{s}^{-1}}\] will be

    A) \[1\,\,h\]                                            

    B) \[1.68\,\,h\]

    C) \[1.28\,\,h\]                      

    D)  \[1.11\,\,h\]

    Correct Answer: B

    Solution :

    Given,\[A=1.11\times {{10}^{11}}{{s}^{-1}}\,\,T=573\,\,K\] \[{{E}_{a}}=39.3\times {{10}^{3}}cal\,\,mo{{l}^{-1}};\,\,R=1.987\,\,cal;\] \[\because \]     \[k=A{{e}^{-{{E}_{a}}/RT}}\] \[\therefore \]  \[\ln k=\ln A-\frac{{{E}_{a}}}{RT}\] or            \[{{\log }_{10}}k={{\log }_{10}}A-\frac{{{E}_{a}}}{2.303RT}\] or            \[{{\log }_{10}}k={{\log }_{10}}1.11\times {{10}^{11}}\]                                 \[-\left\{ \frac{39.3\times {{10}^{3}}}{2.303\times 1987\times 573} \right\}\] or            \[k=1.11\times {{10}^{11}}\]                 \[{{t}_{1/2}}=\frac{0.693}{k}=\frac{0.693}{1.14\times {{10}^{-4}}}\]                 \[=6078s=1.68\,\,h\]


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