NEET Chemistry NEET PYQ-Electrochemistry

  • question_answer
    Standard free energies of formation (in kJ/mol) at 298 K are \[-237.2,\text{ }-394.4\] and \[-8.2\] for\[{{H}_{2}}O(l)C{{O}_{2}}(g)\] ate) and pentane (g), respectively. The value of \[E_{cell}^{o}\] pentane-oxygen fuel cell is                           [AIPMT (S) 2008]

    A) 1.968 V

    B) 2.0968 V

    C) 1.0968 V

    D) 0.0968 V

    Correct Answer: C

    Solution :

    [c] Given,      \[\Delta _{{{H}_{2}}O(l)}^{o}=-237.2\]
    \[\Delta _{C{{O}_{2}}(g)}^{o}=-394.4\]
    \[\Delta G_{{{C}_{5}}{{H}_{12}}(g)}^{o}=-8.2\]
    \[{{C}_{5}}{{H}_{12}}+16{{O}_{2}}\xrightarrow[{}]{{}}5C{{O}_{2}}+6{{H}_{2}}O\]
    \[\Delta {{G}^{o}}=5\times \Delta G_{C{{O}_{2}}}^{o}+6\times \Delta G_{{{H}_{2}}O}^{o}\]
    \[-\left( \Delta G_{{{C}_{5}}{{H}_{12}}}^{o}+\Delta G_{{{O}_{2}}}^{o} \right)\]
    \[=5\times (-394.4)+6\times (-237.2)-(-8.2)+0\]
    \[=-3387\,\text{kJ/mol}\]
    In pentane-oxygen fuel cell 32 electrons are involved.
    \[\Delta {{G}^{o}}=nFE_{cell}^{o}\]
    \[-3387\times {{10}^{3}}=32\times 96500\times E_{cell}^{o}\]
    \[E_{cell}^{o}=\frac{-3.387\times {{10}^{3}}}{32\times 96500}\]
    \[=\frac{3387}{3088}\,=1.0968\,\text{V}\]


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