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JEE Main & Advanced Chemistry Thermodynamics / रासायनिक उष्मागतिकी Question Bank Heat of reaction

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    Heats of combustion \[(\Delta {{H}^{o}})\] for \[C(s),\,{{H}_{2}}(g)\] and \[C{{H}_{4}}(g)\] are \[-94,\,-68\] and \[-213\,kcal/mol.\] respectively. The value of \[\Delta {{H}^{o}}\] for the reaction, \[C(s)+2{{H}_{2}}(g)\,\to \,C{{H}_{4}}(g)\] is                                        [CBSE PMT 2002]

    A)                 ? 85 kcal              

    B)                 ? 111 kcal

    C)                 ? 17 kcal              

    D)                 ? 170 kcal

    Correct Answer: C

    Solution :

           \[{{C}_{(s)}}+2{{H}_{2}}_{(g)}\to C{{H}_{4(g)}}\]                                      ?..(i)            \[{{C}_{(s)}}+{{O}_{2(g)}}\to C{{O}_{2(g)}}\,\,\,\Delta H=-94\,kcal\,mo{{l}^{-1}}\]  ?..(ii)                    \[{{H}_{2(g)}}+\frac{1}{2}{{O}_{2(g)}}\to {{H}_{2}}{{O}_{(l)}}\,\,\,\Delta H=-68\,kcal\,mo{{l}^{-1}}\]?   (iii)                    \[C{{H}_{4}}+3{{/}_{2}}{{O}_{2}}\to C{{O}_{2}}+2{{H}_{2}}O\]                    \[\Delta H=-213\,kcal\,mo{{l}^{-1}}\]                                                   ? (iv)                                 to obtain equation (i) operate-(ii) + 2 × (iii) ? (iv).


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