JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2011

  • question_answer
        Four moles of an ideal gas undergo a reversible isothermal expansion from volume \[{{V}_{1}}\] to volume\[{{V}_{2}}=2{{V}_{1}}\]at temperature T = 400 K. Find the entropy change of the gas.

    A)  \[9.22\times {{10}^{3}}J{{K}^{-1}}\]       

    B)  \[8.22\times {{10}^{2}}J{{K}^{-1}}\]

    C)  \[2.31J{{K}^{-1}}\]                         

    D)  \[10.00\times {{10}^{3}}J{{K}^{-1}}\]

    Correct Answer: A

    Solution :

                    Pressure\[p=nRT/V\]. The work done by the gas during the isothermal expansion is \[W=\int_{{{V}_{1}}}^{{{V}_{2}}}{pdV}=nRT\int_{{{V}_{1}}}^{{{V}_{2}}}{\frac{dV}{V}}=nRT\]in\[\frac{{{V}_{2}}}{{{V}_{1}}}\] Substitute\[{{V}_{2}}=2{{V}_{1}}\]to obtain                 \[W=nRT\]in\[2\]                 \[=(4.00)(8.314)(400)in\,2\]                 \[=9.22\times {{10}^{3}}J{{K}^{-1}}\]


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