AIIMS AIIMS Solved Paper-2001

  • question_answer
    The heat of reaction for: \[{{C}_{10}}{{H}_{g}}(s)+12{{O}_{2}}(g)\xrightarrow{{}}10\,C{{O}_{2}}(g)\] \[+4{{H}_{2}}O(l)\] at constant volume is \[-1228.2\text{ }kcal\] at \[{{25}^{o}}C\]. The heat of reaction at constant pressure and same temperature is:

    A)  \[-1228.2\text{ }kcal\]  

    B)        \[-1229.3\text{ }kcal\]

    C)         \[-1232.9\text{ }kcal\]

    D)         \[-1242.6\text{ }kcal\]

    Correct Answer: B

    Solution :

    \[{{C}_{10}}{{H}_{8}}(s)+12{{O}_{2}}(g)\to 10C{{O}_{2}}(g)+4{{H}_{2}}O(l)\] We know that \[\Delta H=\Delta E+\Delta nRT\] \[\Delta H\]= Heat at constant pressure \[\Delta E\] = Heat at constant volume \[=-1228.2\times {{10}^{3}}cal\] \[\Delta n\]= Change in gaseous moles \[=10-12=-2\] \[T=298K;R=2cal\] \[\therefore \]  \[\Delta H=-1228.2\times {{10}^{3}}+(-2)(2)(298)\] \[=-1229392cal\] \[=-1229.392kcal\]


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