The entropy is higher if the metal is in liquid state than when it is in solid state. The value of entropy change (DS) of the reduction process is more on positive side when the metal formed is in liquid state and the metal oxide being reduced is in solid state. Thus the value of DrG V becomes more on negative side and the reduction becomes easier.

Partial roasting of sulphide ore forms some oxide which then reacts with the remaining sulphide ore to form copper metal by self reduction of the oxide and sulphide a
\(2{ Cu }_{ 2 }S+3{ O }_{ 2 }\quad \longrightarrow \quad 2{ Cu }_{ 2 }O+2{ SO }_{ 2 }\)
\(2{ Cu }_{ 2 }S+{ Cu }_{ 2 }S\quad \longrightarrow \quad { 6Cu }+{ SO }_{ 2 }\)
Thus, to bring about self reduction process, sulphide ore of copper is partially roasted to .

During leaching process, (Au) is first oxidised by \({ O }_{ 2 }\) of the air to \({ Au }^{ + }\)  which then combines with \({ CN }^{ - }\)  ions to form the soluble complex, dicyanoaurate (I) \(4Au(s)+8NaCN(aq)+{ O }_{ 2 }(g)+2{ H }_{ 2 }O(l)\longrightarrow 4Na[Au{ (CN) }_{ 2 }](aq)+4NaOH(aq)+\underset {Sodium dicyanoaurate(I)(Solublecomples) }{ 4NaOH(aq) } \)
Gold is then extracted from this complex by displacement method by using a more electropositive zinc metal. In this method, zinc acts as a reducing agent and it reduces \({ Au }^{ + }\) to Au. Zinc itself gets oxidised to \({ Zn }^{ 2+ }\) ions which combine with \({ CN }^{ - }\) ions to form soluble complex, sodium tetracyano zincate (II).
\(2Na[Au{ (CN) }_{ 2 }](aq)+Zn(s)\longrightarrow 2Au(s)+\underset { Sodium\quad tetracyano\quad zincate(II)(Soluble\quad comples) }{ { Na }_{ 2 }[Zn{ (CN })_{ 4 } } \) 
Thus, extraction of gold by leaching with NaCN involves both oxidation and reduction.

In the thermite process, oxides of metals like iron are reduced by aluminum. This reaction is highly exothermic and a large amount of heat is evolved during the reaction. As a result of large heat, the metal will be in the molten state.
For example,
\(\underset { Iron\quad oxide }{ { Fe }_{ 2 }{ O }_{ 3 } } +2Al(s)\overset { Heat }{ \longrightarrow } { Al }_{ 2 }{ O }_{ 3 }(s)+\underset { Melton }{ 2Fe } +Heat\)
If the molten metal is allowed to fall between the broken parts of a machine, the gaps will be filled up. Therefore, the machine will be repaired.

Nitrates of all metals are soluble in water. Therefore, if metal nitrates are present in the crust of earth, these would be slowly and gradually washed by rain water into the sea. Therefore, metals usually donot occur as nitrates.