BHU PMT BHU PMT (Screening) Solved Paper-2011

  • question_answer
    The bond dissociation energies of gaseous\[{{H}_{2}},C{{l}_{2}}\]and\[HCl\]are 104, 58 and 103 kcal respectively. The enthalpy of formation of \[HCl\]gas would be

    A)  \[-\text{ }44\text{ }kcal\]           

    B)  \[-\text{ }88\text{ }kcal\]

    C)   \[-22\text{ }kcal\]                         

    D)  \[-\text{ }11\text{ }kcal\]

    Correct Answer: C

    Solution :

                     \[\frac{1}{2}{{H}_{2}}+\frac{1}{2}C{{l}_{2}}\xrightarrow{{}}HCl\] \[\Delta H=\Sigma BE\](reactants)\[-\Sigma BE\](products) \[=BE(HCl)-\left[ \frac{1}{2}BE({{H}_{2}})+\frac{1}{2}BE(C{{l}_{2}}) \right]\] \[=-103-\left[ \frac{1}{2}\times (-104)+\frac{1}{2}\times (-58) \right]\] \[=-103-[52-29]\] \[=-103+81\] \[=-22kcal\]


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