Ques. 1AIPMT 2012 (Mains)
The Gibbs energy for the decomposition of Al2O3 at 500 is as follows 23Al2O3 43Al + O2 rG = +960 kJ mol-1 The potential difference needed for the electrolytic reduction of aluminium oxide (Al2O3) at 500 is at least
- 4.5 V
- 3.0 V
- 2.5 V
- 5.0 V
Answer
(3) 2.5 V
Solution
In 23Al2O3 43Al + O2, 43 mol of Al3+ is reduced:
n = 43 3 = 4 electrons
rG = -nFE ⇒ the minimum potential difference = rGnF
= 960 1034 96500
= 2.49 V 2.5 V
∴ As per NCERT, the potential difference needed for the electrolytic reduction of Al2O3 at 500 °C is at least 2.5 V.
Answer: (3)