. Is the reduction of Cr2O3 possible with Al


The value of ∆fG° for formation of Cr203 is -540 kJ/mol and that of A1203 is - 827 kJ/mol. Is the reduction of Cr203 possible with AI?

Hint : Find ∆G°  for both the forward and reverse reactions, if ∆fG° is negative, reaction is feasible.

Best Answer

The two thermochemical equation may be written as

1) 4/3 Cr(s) + O2(g) → 2/3 Cr2O3(s); ∆fG° = - 540kJ

2) 4/3 Al(s) + O2(g) → 2/3 AI2O3(s); ∆fG° = - 827kJ

Subtracting Equation (1) from Eq. (2) we get

2/3CrO3(s) + 4/3 AI(s) → 2/3 Al2O3(s) + 4/3 Cr(s); ∆fG° = - 287 kJ

As ∆fG° comes out to be negative, the reaction is feasible. i.e., AI can be used for the reduction of Cr2O3.

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