Displacement Reaction
Displacement reactions give much more positive evidence about reactivity than comparing the reactions of metals with water or acid. If metal A displaces metal B, then metal A is more reactive then metal B is the more reactive of the two.
We can now, at last, sort out the relative reactivities of lead and copper! If lead oxide heated with copper, nothing happens. If copper (II) oxide is heated with lead, lead oxide is produced. So lead displaces copper from the copper compound. Lead is more reactive than copper.
One famous displacement reaction demonstrates that aluminium is more reactive than iron. It is called the Thermit reaction. Aluminium powder is mixed with iron (III) oxide powder. The mixture is heated to start the reaction. Once started, the reaction is very rapid. A large amount of heat is given off. The products are aluminium oxide and some very hot iron. This reaction has been used to produce molten iron, to weld lengths of railway line together.