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JEE Main & Advanced JEE Main Paper (Held On 25 April 2013)

  • question_answer
                    The Gibbs energy for the decomposition of\[A{{l}_{2}}{{O}_{3}}\]at \[{{500}^{0}}C\] is as follows:                 \[\frac{2}{3}A{{l}_{2}}{{O}_{3}}\to 4/3Al+{{O}_{2}},{{\Delta }_{r}}G=+940\,kJ\,mo{{l}^{-1}}\]                 The potential difference needed for the electrolytic reduction of aluminium oxide at\[{{500}^{0}}C\] should be atleast:     JEE Main Online Paper ( Held On 25  April 2013 )

    A)                 4.5 V                     

    B)                                        3.0 V

    C)                                        5.0 V                     

    D)                                        2.5 V

    Correct Answer: B

    Solution :

                    In the reaction \[\frac{2}{3}A{{l}_{2}}{{O}_{3}}\xrightarrow[{}]{{}}\frac{4}{3}Al+{{O}_{2}}\] For the oxidation half-reaction \[A{{l}^{3+}}+3{{e}^{-}}\xrightarrow[{}]{{}}Al\] no. of electron transfered (n)= 3 \[\Delta {{G}^{o}}=-nF{{E}^{o}}\] \[940=3\times 96500\times {{E}^{o}}\] \[{{E}^{o}}=\frac{940\times {{10}^{3}}J}{3\times 96500}\]\[=3.24\approx 3V\]


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