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JEE Main & Advanced Chemistry Thermodynamics / रासायनिक उष्मागतिकी Question Bank First law of thermodynamics and Hess law

  • question_answer
    Consider the reaction : \[{{N}_{2}}+3{{H}_{2}}\to 2N{{H}_{3}}\] carried out at constant temperature and pressure. If \[\Delta H\] and \[\Delta U\] are the enthalpy and internal energy changes for the reaction, which of the following expression is true            [AIEEE 2005]

    A)                 \[\Delta H=0\]  

    B)                 \[\Delta H=\Delta U\]

    C)                 \[\Delta H<\Delta U\]   

    D)                 \[\Delta H>\Delta U\]

    Correct Answer: C

    Solution :

           At constant P or T                     \[\Delta H=\Delta U+\Delta nRT\]Þ  \[\Delta n={{n}_{p}}-{{n}_{R}}=2-4=-2\]                                 \[\therefore \] \[\Delta H<\Delta U\].


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