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  3. JEE Main & Advanced

JEE Main & Advanced AIEEE Solved Paper-2003

  • question_answer
    If at 298K 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 \[{{H}_{2}}C=C{{H}_{2}}(g)+{{H}_{2}}(g)\xrightarrow{\,}\,{{H}_{3}}C-C{{H}_{3}}(g)\] at 298K will be     AIEEE  Solved  Paper-2003

    A)                                         \[+250\] kJ        

    B)       \[-250\] kJ                          

    C)       \[+125\] kJ        

    D)       \[-125\] kJ

    Correct Answer: D

    Solution :

    \[CH=C{{H}_{2}}+{{H}_{2}}\xrightarrow{{}}C{{H}_{3}}-C{{H}_{3}}\] \[\Delta H={{(BE)}_{reac\tan ts}}-{{(BE)}_{products}}\] \[=4{{(BE)}_{C-H}}+{{(BE)}_{C=C}}+{{(BE)}_{H-H}}\]                                     \[-[6{{(BE)}_{C-H}}+{{(BE)}_{C-C}}]\] = - 125 kJ


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