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JEE Main & Advanced JEE Main Paper (Held On 11-Jan-2019 Evening)

  • question_answer
                            The reaction,\[Mg{{O}_{(s)}}+{{C}_{(s)}}\to M{{g}_{s}}+C{{O}_{g}},\]for which \[{{\Delta }_{r}}{{H}^{o}}=+491.1kJ\,mo{{l}^{-1}}\] and\[{{\Delta }_{r}}{{S}^{o}}=198.0J\,{{K}^{-1}}mo{{l}^{-1}},\]is not feasible at 298 K. Temperature above which reaction will be feasible is [JEE  Main Online Paper (Held on 11-jan-2019 Evening)]

    A) 2040.5 K                     

    B) 1890.0 K

    C) 2480.3 K         

    D)   2380.5 K

    Correct Answer: C

    Solution :

    \[\Delta {{G}^{o}}=\Delta {{H}^{o}}-T\Delta {{S}^{o}}\] For a reaction to be spontaneous \[\Delta {{G}^{o}}\]must be negative i.e., \[T\Delta {{S}^{o}}>\Delta {{H}^{o}}\] \[T>\frac{\Delta {{H}^{o}}}{\Delta {{S}^{o}}}\Rightarrow T>\frac{491.1\times 1000}{198}\] \[T>2480.3K\]


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