In the Ellinggam diagram (graph of ΔrGo vs T) for the formation of oxides, copper-copper oxide line is almost at the top. Hence, oxide ores of copper can be easily reduced to copper by heating with coke. The ΔGo vs T lines for CO show negative slope at high temperature. Hence, it can easily reduce copper oxide to copper. However, ΔGf for sulphide ores are higher than that for CS2 (which is an endothermic compound). Hence, the extraction of copper from pyrite ore is difficult.