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KVPY Sample Paper KVPY Stream-SX Model Paper-4

  • question_answer
    If at 298 K the bond energies of \[C-H,C-C,C=C\] and \[H-H\] bonds are respectively 414, 347, 615 and \[435\,kJ\,mo{{l}^{-1}},\] the value of enthalpy change for the reaction, at 298 K will be

    A) \[+\,250\,kJ\]                

    B) \[-\,250\,kJ\]

    C) \[+\,125\,kJ\]                

    D) \[-\,125\,kJ\]

    Correct Answer: D

    Solution :

    [d] \[C{{H}_{2}}=C{{H}_{2}}+{{H}_{2}}\xrightarrow{{}}C{{H}_{3}}-C{{H}_{3}}\] \[\Delta H={{(BE)}_{\text{reactants}}}-{{(BE)}_{\text{products}}}\] \[=4{{(BE)}_{C-\,H}}+{{(BE)}_{C\,=\,\,C}}+{{(BE)}_{H-\,H}}+[6{{(BE)}_{C\,-\,H}}+{{(BE)}_{C-\,C}}]\] \[=[4\times 414+615+435]-[6\times 414+347]\]


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