Manipal Medical Manipal Medical Solved Paper-2007

  • question_answer
    Standard enthalpy and standard entropy changes for the oxidation of ammonia at 298K   are\[-382.64kJ\,mo{{l}^{-1}}\]and\[-145.6\text{ }J{{K}^{-1}}mo{{l}^{-2}}\] respectively. Standard Gibbs energy change for the same reaction at 298K is

    A)  \[-2221.1kJ\text{ }mo{{l}^{-1}}\]

    B)  \[-339.3\text{ }kJ\text{ }mo{{l}^{-1}}\]

    C)  \[-439.3\text{ }kJ\text{ }mo{{l}^{-1}}\]

    D)  \[-523.2\text{ }kJ\text{ }mo{{l}^{-1}}\]

    Correct Answer: B

    Solution :

     For the oxidation of ammonia at 298 K the standard enthalpy change\[(\Delta H)\]and standard entropy change\[(\Delta S)\]are\[-382.64\text{ }kJ\text{ }mo{{l}^{-1}}\] and\[-145.6\text{ }J{{K}^{-1}}mo{{l}^{-1}}\]respectively. The relationship of Gibbs free energy\[(\Delta G)\]with\[\Delta H\]and\[\Delta S\]is represented in form of following equation. \[\Delta G=\Delta H-T\Delta S\] Given that \[\Delta H=-382.64\text{ }kJ\text{ }mo{{l}^{-1}}\] \[\Delta S=-145.6\text{ }J\text{ }{{K}^{-1}}mo{{l}^{-1}}\] \[=-145.6\times {{10}^{-3}}kJ\,{{K}^{-1}}\] or \[\Delta G=-382.64-(298\times -145.6\times {{10}^{-3}})\] \[=-339.3\text{ }kJ\,mo{{l}^{-1}}\]


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