1.

The value of Delta_(f)G^(@) for formation Cr_(2)O_(3) is -540 kJ mol^(-1) and that of Al_(2)O_(3) is -827 kJ mol^(-1). Is the reduction of Cr_(2)O_(3) possible with aluminium?

Answer»

Solution :The two equations are :
`(4)/(3)Al_((s))+O_(2(g))rarr(2)/(3)Al_(2)O_(3(s))`
`Delta_(f)G^(@)=-827kJmol^(-1)""...(i)`
`(4)/(3)Cr_((s))+O_(2(g))rarr(2)/(3)Cr_(2)O_(3(s))`
`Delta_(f)G^(@)=-540kJmol^(-1)""...(II)`
Subtracting equation (ii) from equation (i), we get
`(4)/(3)AL(s)+(2)/(3)Cr_(2)O_(3)(s)rarr(2)/(3)Al_(2)O_(3)(s)+(4)/(3)Cr(s)`,
`Delta_(f)G^(@)=-287kJmol^(-1)`
As `Delta_(f)G^(@)` of the combined redox REACTION is negative, therefore, reduction of `Cr_(2)O_(3)` by Al is possible.


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