VMMC VMMC Medical Solved Paper-2015

  • question_answer
    The molar internal energy of a gas at temperature T is\[{{U}_{m}}\]  [T]. The molar internal energy at T = 0 is\[{{U}_{m}}\] (0). The correct expression that relates these two with appropriate contributions is

    A)  \[{{U}_{m}}(T)={{U}_{m}}(0)+3RT\][Linear molecule, translation only]

    B) \[{{U}_{m}}(T)={{U}_{m}}(0)+\frac{5}{2}RT\][Linear molecule translation and rotation only]

    C) \[{{U}_{m}}(T)={{U}_{m}}(0)+\frac{3}{2}RT\][Non-linear  molecule, translation and rotation only]

    D) \[{{U}_{m}}(T)={{U}_{m}}(0)+RT\] [Non-linear molecule, translation only]

    Correct Answer: B

    Solution :

    \[\Delta {{U}_{m}}={{C}_{V}}\Delta T\] \[{{\Delta }_{m}}(T)-{{U}_{m}}(0)={{C}_{V}}(T-0)\] \[{{U}_{m}}(T)-{{U}_{m}}(0)=\frac{5}{2}RT\] [\[Cv=\frac{5}{2}R,\] for linear molecule, by taking translational and rotational]\[{{U}_{m}}(T)={{U}_{m}}(0)+\frac{5}{2}RT\]


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