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11th Class Physics Thermodynamical Processes Question Bank Critical Thinking

  • question_answer
    The enthalpies of formation of \[A{{l}_{2}}{{O}_{3}}\] and \[C{{r}_{2}}{{O}_{3}}\] are \[-1596\,kJ\] and \[-1134\,kJ\] respectively. \[\Delta H\] for the reaction \[2Al+C{{r}_{2}}{{O}_{3}}\to 2Cr+A{{l}_{2}}{{O}_{3}}\] is           [KCET 2003]

    A)                 \[-2730\,kJ\]     

    B)                 \[-462\,kJ\]

    C)                 \[-1365\,kJ\]     

    D)                 \[+\,2730\,kJ\]

    Correct Answer: B

    Solution :

           \[2Al+\frac{3}{2}{{O}_{2}}\to A{{l}_{2}}{{O}_{3}},\,\,\,\Delta H=-1596\,kJ\]          ?..(i)            \[2Cr+\frac{3}{2}{{O}_{2}}\to C{{r}_{2}}{{O}_{3}},\,\,\,\Delta H=-1134\,kJ\]               ?..(ii)            By (i) ? (ii)                                 \[2Al+C{{r}_{2}}{{O}_{3}}\to 2Cr+A{{l}_{2}}{{O}_{3}},\,\,\,\Delta H=-462\,kJ\].


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