Types of Reaction

Double Displacement Reaction

Reactions in which ions are exchanged between two reactants are called double displacement reactions. In other words, in case of double displacement reaction, two compounds displace each other's ions. You may recall that in case of single displacement reaction, a more reactive metal displaced a less reactive metal from a compound. But in double displacement reaction displacement takes place from both the reactants.

AB + CD → AC + BD

In this imaginary example, AB and CD are reactants. Both the compounds displace ions from each other to form new compounds. In this case, products are AC and BD.

More Examples

Example 1: When solution of barium chloride reacts with the solution of sodium sulphate, white precipitate of barium sulphate is formed along with sodium chloride.

BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl

Example 2: When sodium hydroxide (a base) reacts with hydrochloric acid, sodium chloride and water are formed.

NaOH + HCl → NaCl + H₂O

Double displacement reaction, in which precipitate is formed, is also known as precipitation reaction.

Neutralisation reactions are also examples of double displacement reaction.

Exothermic and Endothermic Reaction

Reactions which produce energy are called exothermic reaction. On the other hand, reactions which absorb energy are called endothermic reaction.

Most of the combination reactions are exothermic. Most of the decomposition reactions are endothermic. Respiration is a combination reaction in which energy is released.

Example of Combination Reaction: When quick lime (calcium oxide) is added to water, it combines to form calcium hydroxide and releases energy. Cooking involves chemical reactions which are endothermic as cooking is possible because of heating.

Oxidation and Reduction Reaction:

Oxidation: Addition of oxygen or non-metallic element or removal of hydrogen or metallic element from a compound is known as oxidation. Elements or compounds in which oxygen or non-metallic element is added or hydrogen or metallic element is removed are called to be oxidized. So, oxidation can involve any of the following:

• Addition of oxygen
• Addition of non-metallic element
• Removal of hydrogen
• Removal of metallic element

Oxidizing agent: Compounds which can add oxygen or a non-metallic compound or remove hydrogen or metallic element are known as oxidizing agents.

Reduction: Addition of hydrogen or metallic element or removal of oxygen or non-metallic element from a compound is called reduction. The compound or element which goes under reduction is called to be reduced. So, reduction can involve any of the following:

• Addition of hydrogen
• Addition of metal
• Removal of oxygen
• Removal of non-metal

To make it easier to understand, here is table to show comparision between oxidation and reduction.

Reducing agent: Compounds or elements which can cause reduction are called reducing agents.

In a chemical reaction, both oxidation and reduction take place simultaneously and such reactions are also known as REDOX REACTIONS. In the word REDOX, Red stands for reduction and Ox stands for oxidation.

Example: When iron reacts with air, it forms iron oxide (rust). This reaction is also called Rusting of Iron.

4Fe + 3O₂ → 2Fe₂O₃

In this reaction, oxygen is added to iron, thus, iron is oxidized. Here oxygen is oxidizing agent.

Example: When cupric oxide reacts with hydrogen, it gives copper and water.

CuO + H₂ → Cu + H₂O

In this reaction, oxygen is removed from copper and oxygen is added to hydrogen. So, cupric oxide is reduced to copper and hydrogen is oxidized to water. Cupric oxide is oxidizing agent and hydrogen is reducing agent.

Example: When sodium hydroxide reacts with hydrochloric acid, it gives sodium chloride and water.

NaOH + HCl → NaCl + H₂O

In this reaction, sodium hydroxide is reduced to sodium chloride since hydrogen is removed from sodium hydroxide. Hydrochloric acid is oxidized to water, since oxygen is added to hydrogen chloride and non-metallic element chloride is removed. Sodium hydroxide is oxidising agent and hydrochloric acid is reducing agent.

In this reaction oxidation and reduction both takes place simultaneously, thus it is an example of redox reaction.

Significance of Oxidation Reduction in Everyday Life:

1. Respiration is oxidation reaction in which food is oxidized to produce energy.
2. Iron gets oxidized to form rust, which leads to corrosion of iron in the long run.
3. Most of the metals react with atmospheric oxygen and it leads to formation of a layer on the metal article. The metal gets corroded in the long run.
4. Rusting of iron can be prevented by painting the iron article. This can also be prevented by applying a layer of zinc over iron article. This process is known as galvanization.
5. Fried food gets oxidized when exposed to air. This spoils the taste of the food and the food becomes unfit for consumption. The spoiling of fried food because of oxidation is called rancidity. Fried food is often packed in airtight packets to prevent rancidity.
6. We are able to utilize various types of fuel because of oxidation. Oxidation of fuel helps in producing energy.

Summary