Reactions:
Metals with acids:
Many metals react with dilute acids to produce a salt and hydrogen. For example,
Mg (s) + HCl -> (aq) MgCl + H2
In the above reaction, the salt magnesium chloride is formed. In all reactions of metals with hydrochloric acid, a metal chloride and hydrogen gas are formed.
Note how I say ‘many’ metals react with dilute acid, not all. Only metals that are more reactive than hydrogen react with dilute acids to produce hydrogen gas. Metals like copper and silver will not react with the acids.
Decomposition:
The more reactive a metal is, the more difficult it is to decompose its oxides, i.e. reduce the oxide to the metal.
Oxides of copper, as well as oxides of those metals above copper in the reactivity series, will need the help of reducing agents such as carbon, along with the heat required for decomposition, to turn them into their respective metal oxides. Below copper, there is no need for the reducing agent, for the oxides of those metals simply decompose on heating. However, metal oxides of magnesium, which is a highly reactive metal, will not decompose on heating, even in the presence of a reducing agent. Same goes for the oxides of metals above magnesium in the reactivity series.
Other than carbon, hydrogen is also at times used as a reducing agent during decomposition. However, it only reduces the oxides of iron and the metals below it in the reactivity series, while the oxides of metals more reactive than iron will stay unreacted.
Let us now learn why some metals react while others don’t.