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JEE Main & Advanced Sample Paper JEE Main Sample Paper-33

  • question_answer
    At \[{{727}^{o}}C,\,\,{{N}_{2}}(g)+3{{H}_{2}}(g)\to 2N{{H}_{2}}(g);\,\Delta {{H}^{o}}=-123.77KJmo{{l}^{-1}}\];
    Substance   \[{{N}_{2}}\]    \[{{H}_{2}}\]    \[N{{H}_{3}}\],
    \[{{C}_{p}}\]          3.5R 3.5R 4R
    The heat of formation of ammonia at in \[KJ\text{ }mo{{l}^{-1}}\]at \[{{27}^{o}}C\] is:

    A)  \[+44.42\]         

    B)     \[-44.42\]

    C)  \[+88.85~\]                       

    D)  \[-88.85\]

    Correct Answer: B

    Solution :

    Using Kirchhoff?s equations,             \[\Delta {{H}_{2}}(1000K)\,=\Delta {{H}_{1}}(300K)\,+\Delta {{C}_{p}}(1000-300)\]             \[\Delta {{H}_{2}}(1000K)\,=-123.77\,KJ\,mo{{l}^{-1}}\]             \[\Delta {{H}_{1}}(300K)=?\] \[\Delta {{C}_{p}}=2{{C}_{p}}(N{{H}_{3}})-[{{C}_{p}}({{N}_{2}})\,+3{{C}_{p}}({{H}_{2}})]\] \[=-6R\times 8.314\,\times {{10}^{-3}}\,KJ\,mo{{l}^{-1}}\,{{K}^{-1}}\] \[\therefore \,\,-123.\,77=\Delta {{H}_{1}}(300K)\,-6\times 8.314\,\times {{10}^{-3}}\times 700\]\[\therefore \,\,\,\Delta {{H}_{1}}(300K)\,=-88.85\,KJ\] for two moles of \[N{{H}_{3}}\] \[\therefore \,\,\,N{{H}_{3}}\,\Delta {{H}_{1}}(300K)=-\,88.85\,KJ\] \[\therefore \,\,\,\,\Delta {{H}_{1}}=-44.42KJ\,mo{{l}^{-1}}\]


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