The value of 
for the formation of Cr2 O3 is – 540 kJmol−1and that of Al2 O3 is – 827 kJmol−1. Is the reduction of Cr2 O3 possible with Al?
The value of Δ fG0 for the formation of Cr2O3 is – 540 kJ mol-1 which are higher than that of Al2O3 is – 827 Kjmol-1. Thus, Al can reduce Cr2O3 to Cr. Hence, the reduction of Cr2O3 with Al is possible.
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