KVPY Sample Paper KVPY Stream-SX Model Paper-6

  • question_answer
    If enthalpies of methane and ethane are respectively \[320\]and \[560\]calories, then the bond Energy of C ? C bond is:

    A) \[50\]Calories                 

    B) \[80\] calories

    C) \[40\] Calories                

    D) \[120\] calories

    Correct Answer: B

    Solution :

    given, enthalpy of \[C{{H}_{4}}=320cal\]
    Enthalpy of \[{{C}_{2}}{{H}_{6}}=560\,cal\]
    \[C{{H}_{4}}(g)\xrightarrow{{}}C(g)+4H(g)+4H(g);\Delta H=320cal\]\[4\Delta {{\operatorname{H}}_{\operatorname{C}-H}}=320\,cal\]
    \[\therefore \]      \[\Delta {{H}_{c-H}}=\frac{320}{4}=80cal\]
    \[{{C}_{2}}{{H}_{6}}(g)\xrightarrow{{}}2C(g)+6H(g);\]\[\Delta \operatorname{H}=560\operatorname{cal}\]
    \[\therefore \]\[6\Delta {{H}_{C-H}}+\Delta {{H}_{C-C}}=560\,cal\]
    \[\therefore \]\[\Delta {{H}_{C-C}}=560-6\Delta {{H}_{C-H}}\]
    \[=560-6\times 80\]
    \[=560-480=80\,calories\]


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