1.

The Gibbs energy for the decomposition of `Al_(2)O_(3)` at `500^(@)C` is as follows: `(2)/(3)Al_(2)O_(3) rarr (4)/(3)Al + O_(2), Delta_(r)G = +966kJ mol^(-1)` The potential difference needed for electrolytic reeduction of `Al_(2)O_(3)` at `500^(@)C` is at least:A. 5.0 VB. 4.5 VC. 3.0 VD. 2.5 V

Answer» Correct Answer - D
The ionic reactions are : 2/3 x `(2Al^(3+)) + 4e^(-) to ` 4/3 Al
2/3 x `(3O^(2-)) to O_2 + 4e^(-)`
Thus, no of electrons transferred, n=4, `DeltaG`= -nFE = - 4 x 96500 x E
or 966 x `10^3`= -4 x 96500 x E
`rArr E= - (966xx10^3)/(4xx96500)`=-2.5 V


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