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JEE Main & Advanced Chemistry Thermodynamics / रासायनिक उष्मागतिकी Question Bank Bond energy

  • 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 [MP PET 1997; MP PMT 1999, 2001]

    A)                 ? 44 kcal              

    B)                 44 kcal

    C)                 ? 22 kcal              

    D)                 22 kcal

    Correct Answer: C

    Solution :

           Aim: \[\frac{1}{2}{{H}_{2}}+\frac{1}{2}C{{l}_{2}}\to HCl\]            \[\Delta H=\sum B.E{{.}_{\text{(Products)}}}-\sum B.E{{.}_{\text{(Reactants)}}}\] \[=B.E.(HCl\,)-\left[ \frac{1}{2}B.E.({{H}_{2}})+\frac{1}{2}B.E.(C{{l}_{2}}) \right]\] \[=-103-\left[ \frac{1}{2}(\,-104\,)+\frac{1}{2}(\,-58) \right]\]                                 \[=-103-(\,-52-29\,)=-22\,\,kcal\].


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