Consider the Unbalanced Reaction:

Question

Al2O3(s) + CO(g) → Al(s) + CO2(g)

Estimate ∆G at 298 K if 7.1 moles of Al2O3(s) is reacted.

Answer 1

I will assume you do not have dH or dS available. Look up dGo for the reactant and products. Balance the equation.
Al2O3 + 3CO ==> 2Al + 3CO. Then
dGo rxn - (n*dGo products) - (n*dGo products). That will give you dGo for the reaction for 1 mol Al2O3. You want dGo for 7.1 mol Al2O3.
Convert from 1 mol to 7.1 mol and you hve it.