Question

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 "V "`
B. `4.5 "V"`
C. `3.0" V "`
D. `2.5" V "`

Answer 1

Correct Answer - D
(d) The ionic reactions are : `2//3 Al_(2)^(3+)+4e^(-) to 4//3 Al`
`2//3 O_(3)^(2-) to O_(2)+4e^(-)`
No. of electrons =4
`DeltaG=-nFE_(cell)`
`E_(cell)=-(DeltaG)/(nF)=(966xx10^(3)(CV))/(4xx96500(V))=2.5" V"`.