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

  • question_answer
    The enthalpy of combustion of benzene from the following data will be                 (i) \[6C(s)+3{{H}_{2}}(g)\to {{C}_{6}}{{H}_{6}}(l);\,\Delta H=+45.9\,kJ\]                 (ii) \[{{H}_{2}}(g)+\frac{1}{2}{{O}_{2}}(g)\to {{H}_{2}}O(l);\,\Delta H=-285.9\,kJ\]                 (iii) \[C(s)+{{O}_{2}}(g)\to C{{O}_{2}}(g);\,\Delta H=-393.5\,kJ\]

    A)                 + 3172.8 kJ         

    B)                 ? 1549.2 kJ

    C)                 ? 3172.8 kJ         

    D)                 ? 3264.6 kJ

    Correct Answer: D

    Solution :

           Multiplying eq. (ii) by (iii) and eq. (iii) by (vi), and then add            \[6\,C+3{{H}_{2}}+\frac{15}{2}{{O}_{2}}\to \]\[6\,C{{O}_{2}}+6{{H}_{2}}O;\,\,\Delta H=3218.7\]                                 Subtract eq. (i) from the above equation and find the required result.


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