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JIPMER Jipmer Medical Solved Paper-1995

  • question_answer
    If bond energies of \[N\equiv N,\] \[H-H\]and \[N-H\] bonds are 945, 437 and 389 kJ respectively, AH for the following gaseous reaction is \[{{N}_{2}}+3{{H}_{2}}\xrightarrow{{}}2N{{H}_{3}}\]

    A)  \[-78\,kJ\]

    B)                                         \[-156\,kJ\]                       

    C)         \[-1478\,kJ\]                    

    D)         \[+1478\,kJ\]

    Correct Answer: A

    Solution :

    \[{{N}_{2}}+3{{H}_{2}}\xrightarrow{{}}2N{{H}_{3}}\]For this reaction, Heat evolved \[=6\times \](\[N-H\]bond energy) \[-\] [3 (\[H-H\]bond energy) + (\[N\equiv N\]) bond energy] = 6 (389) \[-\] [3 (437) + (945)] = 2334 \[-\] (1311 + 945) = 2334 \[-\] 2256 = 78 kJ \[\therefore \]  \[\Delta H=-78\,kJ\]


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