Type of Reactions
- Double Displacement Reaction
- Exothermic Reaction
- Endothermic Reaction
- Oxidation Reduction reaction
- Acid – Base Neutralization Reaction
Double Displacement Reaction: Reactions in which ions are exchanged between two reactants forming new compounds are called double displacement reactions.
AB + CD ⇨ AC + BD
Example: 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
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 Heat are called exothermic reaction.
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) + Heat
Any combustion reaction is exothermic reaction. so any fuel when undergo reaction with oxygen it forms Carbon dioxide , water and heat.
On the other hand, reactions which absorb heat are called endothermic reaction.
NH4Cl(s) → NH3(g) + HCl (g) – heat
Most of the decomposition reactions are endothermic, generally.
Respiration is a decomposition reaction in which energy is released. When quick lime (calcium oxide) is added to water, it reacts with water (undergoes hydrolysis) and releases heat. Cooking involves chemical reactions which are endothermic as cooking is possible because of heating.
Acid – Base Neutralization Reaction: In this reaction acid is mixed with base to form salt and water.
When sodium hydroxide (a base) reacts with hydrochloric acid, sodium chloride and water are formed.
NaOH + HCl ⇨ NaCl + H2O
Oxidation and Reduction Reaction:
(i) addition of Oxygen
or (ii) removal of Hydrogen to any element or compound
Elements or compounds in which oxygen or non-metallic element is added or hydrogen or metallic element is removed are called to be oxidized.
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.
Reducing agent: Compounds or elements which can cause reduction are called reducing agents.
In a chemical reaction oxidation and reduction both 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)
4Fe + 3O2 ⇨ 2Fe2O3
In this reaction, oxygen is added to iron, thus, iron is oxidized. Here oxygen is oxidizing agent.
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.
Reducing Agent : H2
Oxidizing Agent : CuO
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:
- Respiration is oxidation reaction in which food is oxidized to produce energy and Carbon dioxide and water.
- Iron gets oxidized to form rust; which leads to corrosion of iron in the long run.
- Most of the metals react with atmospheric oxygen and it leads to formation of a metal oxide layer on the metal article. The metal gets corroded in the long run.
- 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.
- 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.
- Fuel reaction with oxygen is redox reaction which gives heat and other form of energy.