JEE Main & Advanced Sample Paper JEE Main - Mock Test - 32

  • question_answer
    In the process: \[{{H}_{2}}O(s),-10{}^\circ C,1atm)\xrightarrow{{}}{{H}_{2}}O(l,\,\,10{}^\circ C,\,1atm){{C}_{P}}\] for \[ice=9\,cal\,{{\deg }^{-1}}mo{{l}^{-1}},\]\[{{C}_{P}}\] for \[{{H}_{2}}O=18cal{{\deg }^{-1}}mo{{l}^{-1}}.\]Latent heat of fusion of \[ice=1440\,cal\,mo{{l}^{-1}}\] at\[0{}^\circ C\]. The entropy change for the above process in \[cal\,\,{{\deg }^{-1}}mo{{l}^{-1}}\] and the total number of steps in which the third law of thermodynamics used are

    A) \[0.336,\text{ }1\]            

    B)       \[0.6258,\text{ }2\]

    C) \[5.528,\text{ }3\]            

    D)        \[0.647,\text{ }0\]

    Correct Answer: B

    Solution :

    [b] Step 1. (Using the third law of thermodynamics): (For changing \[{{H}_{2}}O(s)\,\,(-10{}^\circ C,\,1atm)\xrightarrow{{}}{{H}_{2}}O\,(s,\,0{}^\circ C\,1atm)\] \[\Delta {{S}_{1}}=\int\limits_{-10}^{0}{n\frac{{{C}_{P}}}{T}}dT=1\times 9\times 2.3\times \log \frac{273}{263}\] \[=0.336\,cal\,\,{{\deg }^{-1}}mo{{l}^{-1}}\] Step 2 (Using the second law of thermodynamics): \[{{H}_{2}}O(s)\,\,(0{}^\circ C,\,1atm)\xrightarrow{{}}{{H}_{2}}O(l)\,(0{}^\circ C,\,1atm)\] \[\Delta {{S}_{2}}=\frac{{{q}_{rev}}}{T}=\frac{1440}{273}=5.258\,cal\,\,{{\deg }^{-1}}\,mo{{l}^{-1}}\] Step 3 (Using the third law of thermodynamics): \[{{H}_{2}}O(l)\,(0{}^\circ C,\,1atm)\xrightarrow{{}}{{H}_{2}}O(l)\,\,(10{}^\circ C,\,1atm)\] \[\Delta {{S}_{3}}=\int\limits_{0}^{-10}{n\frac{{{C}_{P}}}{T}}dT=1\times 18\times 2.3\times \log \frac{283}{273}\] \[=0.647\,\,cal\,\,{{\deg }^{-1}}mo{{l}^{-1}}\] \[\Delta S=\Delta {{S}_{1}}+\Delta {{S}_{2}}+\Delta {{S}_{3}}=0.336+5.258+0.647\] \[=6.258\,cal\,\,{{\deg }^{-1}}\,mo{{l}^{-1}}\]


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