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Punjab Medical Punjab - MET Solved Paper-1999

  • question_answer
    If enthalpies of formation for \[{{C}_{2}}{{H}_{4}}(g),\,\,C{{O}_{2}}(g)\]and\[{{H}_{2}}O\,\,(l)\]at\[{{25}^{o}}C\] and \[1\,\,atm\] pressure are\[52,\] \[-394\] and\[-286\,\,kJ/mol\] respectively, then total enthalpy of combustion is

    A) \[+1412\,\,kJ/mol\]

    B) \[+141.2\,\,kJ/mol\]

    C) \[-141.2\,\,kJ/mol\]

    D) \[-14.2\,\,kJ/mol\]

    Correct Answer: C

    Solution :

    Given: Enthalpies of\[{{C}_{2}}{{H}_{4}}(g),\,\,C{{O}_{2}}(g)\]and\[{{H}_{2}}O\,\,(l)\]\[52,\,\,-394\]and\[-286\]respectively. We know that                 \[{{C}_{2}}{{H}_{4}}+3{{O}_{2}}\xrightarrow{{}}2C{{O}_{2}}+2{{H}_{2}}O\] Therefore, total enthalpy of their combustion \[=2\times (-394)+2\times (-286)-(52)\] \[=-1412\,\,kJ/mol\]


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