Reactivity Series

We have seen that, 

Some metals react immediately and vigorously with reactants, while others react slowly , or when the reaction mixture is heated/catalysed. Some do not react at all. 

Metals react based on their reactivity.  

Reactivity is the tendency of chemical substances to form products by itself .

• Reactivity series is an arrangement of metals and non-metals based on their tendencies to react with certain tendencies. 
• The elements are arranged in decreasing order of their reactivity .

• The arrangement of metals in a vertical column in the degree of their decreasing reactivities (quality of being reactive) is called the reactivity series of metals.
• The most reactive metal is placed at the top whereas the least reactive metal is placed at the bottom .

Some common reactions of metals

• Sodium and Potassium can react vigorously with oxygen, water, and acids, as soon as they come into contact with them.
• On the other hand, heat is required for the reaction of magnesium with oxygen or air, or the reaction of magnesium with water. 
• Thus, we can say that magnesium is less reactive than Sodium or Potassium.
• Similarly, we can say that Silver, Mercury, Gold, and Platinum are the least reactive metals as they rarely react with chemicals without external help. 

Here's a list of Metal's reaction with Oxygen, Water, and common acids 

Role of hydrogen in determining the reactivity series

In displacement reactions, a more reactive element displaces a less reactive element.

• If a metal is above Hydrogen in the reactivity series, then it will displace hydrogen from water and acids, and hence produce hydrogen gas in the reaction.

• These lose electrons more readily than hydrogen, reactions with other substances are faster .
• Metals like Potassium, Sodium, Calcium, Magnesium, Aluminium, Zinc, Iron, Tin and Lead are more reactive than hydrogen.

• Similarly, if a metal is below Hydrogen in the reactivity series, then it cannot displace hydrogen from water and acids, and thus, will not produce hydrogen gas upon reaction with water and acids.
• These lose electrons less readily than hydrogen, thus it reacts slowly with other substances.
• Metals like Gold, Silver, Copper and Mercury are less reactive than hydrogen and hence do not displace hydrogen from its salts/solutions.

Reaction of Metals with Other Metal Salts

What is a metal salt? 

A metal salt is a compound formed when Hydrogen of an acid is replaced by a metal .

For Example : 

In Zinc Sulphate, Zinc is a metal and Sulphuric Acid is an acid. Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas.

Zn (s) + H 2 SO 4 (aq) ---> ZnSO 4 (aq)+ H 2 (g)

This Zinc Sulphate is a Metal Salt , as it is formed by replacement of Hydrogen from H2SO 4  to form ZnSO 4 .

What is a Solution of Metal Salt?

• It is a mixture of Metal Salt in water .
• Example : Zinc Sulphate (ZnSO 4 )  is a metal salt. But Zinc Sulphate (ZnSO 4 ) (aq) is a solution of metal salt.

Displacement Reactions :

When a more reactive metal is placed in a salt solution of a less reactive metal, the more reactive metal displaces the less reactive metal from its salt solution and forms a salt solution via displacement reaction.

Here, Metal A is more reactive than Metal B. Thus, it pushes metal B out of its salt solution.

For example : Zinc placed in Copper sulphate solution.

• We know that Zinc is more reactive than Copper (refer: reactivity series)
• When we put a piece of zinc metal in a copper sulphate solution, 
• The zinc metal, being more reactive, displaces copper from the copper sulphate and forms zinc sulphate.  
• This is called a displacement reaction.
• However if we put a piece of copper metal in a zinc sulphate solution, no displacement takes place 
• This is because copper is less reactive than zinc.