Thermodynamic Principle in Extraction of Metals
The free energy change( ΔG) occurring during the reduction processes help in deciding the suitable method for reduction.
For the spontaneous reduction of an oxide, halide or sulphide by an element, the essential condition is that there is a decrease in the free energy of the system(-ve ΔG).
More the negative value of ΔG, the higher is the reducing power of an element. ΔG can be given as
ΔG = ΔH – TΔS
where, ΔH = enthalpy change; ΔG = Gibbs free energy T = temperature; ΔS = entropy change
For the reduction of a metal oxide with a reducing agent, the plot of ΔG ° against temperature is studied, which is called Ellingbam diagram.