JEE MAIN - Chemistry (2010 - No. 20)
The Gibbs energy for the decomposition of Al2O3 at 500oC is as follows :
$${2 \over 3}A{l_2}{O_3}$$ $$\to$$ $${4 \over 3}Al + {O_2}$$, $${\Delta _r}G$$ = + 966 kJ mol–1
The potential difference needed for electrolytic reduction of Al2O3 at 500oC is at least :
$${2 \over 3}A{l_2}{O_3}$$ $$\to$$ $${4 \over 3}Al + {O_2}$$, $${\Delta _r}G$$ = + 966 kJ mol–1
The potential difference needed for electrolytic reduction of Al2O3 at 500oC is at least :
4.5 V
3.0 V
2.5 V
5.0 V
Explanation
$$\Delta G = - nFE$$
or $$E = {{\Delta G} \over { - nF}} = {{966 \times {{10}^3}} \over {4 \times 36500}}$$
$$ = - 2.5\,\,V$$
$$\therefore$$ The potential difference needed for the reduction $$=2.5$$ $$V$$
or $$E = {{\Delta G} \over { - nF}} = {{966 \times {{10}^3}} \over {4 \times 36500}}$$
$$ = - 2.5\,\,V$$
$$\therefore$$ The potential difference needed for the reduction $$=2.5$$ $$V$$
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