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NEET Sample Paper NEET Sample Test Paper-73

  • question_answer
    What is the value of \[\Delta E\] (heat change at constant volume) for reversible isothermal evaporation of 90 g water\[100{}^\circ C\]. Assuming water vapour behaves as an ideal gas and\\[{{\left( \Delta {{H}_{vap}} \right)}_{water}}=540\,cal\,\,{{g}^{-1}}\].                                           

    A) \[9\times {{10}^{3}}\,cals\]                  

    B) \[6\times {{10}^{3}}\,cals\]

    C) 4.49 cals                       

    D) none of these  

    Correct Answer: D

    Solution :

    Heat of system \[{{\left( \Delta H \right)}_{v}}\ =\,\,m\,\,\times \,\,L\nu \] \[= 90 \times  540 = 486000 cal\] \[\Delta H=\Delta E+P({{V}_{v}}-{{V}_{1}})\,=\Delta E+nRT\] or \[48600= \Delta E + \frac{90}{18} \times  2 \times  373\] \[\Delta E=48600-3730=44870\,\,cal\]


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