JEE Main & Advanced JEE Main Paper (Held On 09-Jan-2019 Evening)

  • question_answer
    The entropy change associated with the conversion of 1 kg of ice at 273 K to water vapours at 383 K is: (Specific heat of water liquid and water vapour are \[4.2\text{ }kJ\text{ }{{K}^{-1}}\,k{{g}^{-}}^{1}\] and \[2.0\text{ }kJ\text{ }{{K}^{-1}}\,k{{g}^{-}}^{1}\]heat of liquid fusion and vapourisation of water are \[334\text{ }kJ\text{ }k{{g}^{-1}}\] and \[2491\text{ }kJ\text{ }k{{g}^{-1}}\], respectively), \[(log\text{ }273\,\,\,=\,\,2.436\], \[log\text{ }373=2.572,\text{ }log\text{ }383\,\,\text{=}\,\,2.583)\] [JEE Main Online Paper (Held On 09-Jan-2019 Evening]

    A) \[2.64\text{ }kJ\text{ }k{{g}^{-1}}\text{ }{{K}^{-1}}\]                        

    B) \[9.26\text{ }kJ\text{ }k{{g}^{-1}}\text{ }{{K}^{-1}}\]

    C) \[7.90\text{ }kJ\text{ }k{{g}^{-1}}\text{ }{{K}^{-1}}~\]

    D)             \[8.49\text{ }kJ\text{ }k{{g}^{-1}}\text{ }{{K}^{-1}}\]

    Correct Answer: B

    Solution :

    \[\underset{273K}{\mathop{{{H}_{2}}O}}\,(s)\to \underset{273K}{\mathop{{{H}_{2}}O(\ell )}}\,\Delta {{S}_{1}}=\frac{\Delta {{H}_{fusion}}}{T}=\frac{334}{273}=1.22\] \[\underset{273K}{\mathop{{{H}_{2}}O}}\,(\ell )\to \underset{373K}{\mathop{{{H}_{2}}O}}\,(\ell )\Delta {{S}_{2}}=4.2\times \ell n=\left( \frac{373}{273} \right)=1.31\] \[\underset{373K}{\mathop{{{H}_{2}}O}}\,(\ell )\to \underset{373K}{\mathop{{{H}_{2}}O}}\,(g)\Delta {{S}_{3}}=\frac{\Delta {{H}_{vap}}}{T}=\frac{2491}{373}=6.67\] \[\underset{373K}{\mathop{{{H}_{2}}O}}\,(g)\to \underset{383K}{\mathop{{{H}_{2}}O}}\,(g)\Delta {{S}_{4}}=2\ell n\frac{383}{373}=0.529\] \[\Delta \,{{S}_{total}}\,\,=\,\,9.26\text{ }kJ\text{ }k{{g}^{-1}}\text{ }{{K}^{-1}}\]


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