Q)why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?
Ans) The Standard free energy of formation of Cu2S is greater than those of CS2 & H2S .Hence , niether carbon nor hydrogen can reduce Cu2S to Cu metal. On the other hand , standard free energy of formation of Cu2O is much lower than that of CO2 & hence , carbon can easily reduce Cu2O to Cu. Cu2O+C (s) -> Cu(s) +CO(g)