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JEE Main & Advanced JEE Main Paper (Held On 11 April 2014)

  • question_answer
    The molar heat capacity \[({{C}_{p}})\] of \[C{{D}_{2}}O\]is 10 cals at 1000 K. The change in entropy associated with cooling of 32 g of \[C{{D}_{2}}O\]vapour from 1000 K to 100 K at constant pressure will be: (D = deuterium, atomic mass = 2 u)   [JEE Main Online Paper ( Held On 11 Apirl  2014 )

    A) \[\text{23}\text{.03cal}\,\text{de}{{\text{g}}^{\text{-1}}}\]        

    B) \[\text{-23}\text{.03cal}\,\text{de}{{\text{g}}^{\text{-1}}}\]

    C) \[\text{2}\text{.303cal}\,\text{de}{{\text{g}}^{\text{-1}}}\]        

    D) \[\text{-2}\text{.303cal}\,\text{de}{{\text{g}}^{\text{-1}}}\]

    Correct Answer: B

    Solution :

                    Given, \[{{C}_{p}}=10\] cals at 1000 K \[{{T}_{1}}=1000K.{{T}_{2}}=100K\] \[m=32g\] \[\Delta S=?\]at constant pressure \[\Delta S={{C}_{p}}\ln \frac{{{T}_{2}}}{{{T}_{1}}}\] \[=2.303\times {{C}_{p}}\log \frac{{{T}_{2}}}{{{T}_{1}}}\] \[=2.303\times 10\log \frac{100}{1000}\]\[=-23.03cal\,{{\deg }^{-1}}\]


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