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Haryana PMT Haryana PMT Solved Paper-2000

  • question_answer
    The standard heats of formation of \[N{{O}_{2}}(g)\] and \[{{N}_{2}}{{O}_{4}}(g)\] are \[8.0\] and \[2.0kcal\,\,mol{{e}^{-1}}\]respectively.   The   heat   of dimerisation of \[N{{O}_{2}}\] in kcal is:

    A)  \[-14.0\]             

    B)  \[-12.0\]

    C)  \[-6.0\]               

    D)  \[-10.0\]

    Correct Answer: A

    Solution :

    Sol.         \[\frac{1}{2}{{N}_{2}}+{{O}_{2}}\xrightarrow{{}}N{{O}_{2}};\]     \[\Delta H=8kcal\] \[{{N}_{2}}+2{{O}_{2}}\xrightarrow{{}}{{N}_{2}}{{O}_{4}};\]   \[\Delta H=2kcal\] Multiplying Eq. (i) by 2 and substracting Eq. (ii) from it.              \[2N{{O}_{2}}\xrightarrow{{}}{{N}_{2}}{{O}_{4}};\]    \[\Delta H=-14.0kcal\]              


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