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Free energies of formation (Delta(f) G^(...

Free energies of formation `(Delta_(f) G^(Ө))` of `MgO(s)` and `CO_((g))` at `1273 K` and `2273 K` are given below :
`Delta_(f) G^(Ө) (MgO_((s) )) = -941 kJ//mol at 1273 K`
`Delta_(f) G^(Ө) (MeO_((s))) = -314 kJ//mol at 2273 K`
`Delta_(f) G^(Ө) (CO_((g))) = - 439 kJ//mol at at 1273 K`
`Delta_(f) G^(Ө) (CO_((g))) = -628 kJ//mol at 2273 K`
On the basis of above data, predict the temperature at which carbon can be used as a reducing for agent `MgO_((s))`.

Text Solution

Verified by Experts

The reduction of MgO with carbon is expressed as :
`MgO(s) + C(s) to Mg(s) + CO(g)`
Free energy `(DeltaG)` for the reaction may be calculated as :
`" " DeltaG = Delta_f G [CO(g)] - Delta_f G[MgO(s)]`
At 1273 K `" " Delta G =-439-(-91) =+ 502 ` KJ/mol
At 2273 K `" " DeltaG =-628 -(-314) =-314 ` KJ/mol
Since `DeltaG` is negative at 2273 K, the reduction is feasilbe at this temperature . Hence, carbon can be used as a reducing agent at 2273 K.
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