Chemical Reactions


When we mix two or more materials , there may be a change in their states, texture and result in a new output. Such a phenomenon is understood to be chemical reaction where one material reacts with another material at molecular and atomic levels.

In a chemical reaction, the atoms and molecules that interact with each other are called reactants. The atoms and molecules produced by the reaction are called products. In a chemical reaction, only the atoms present in the reactants can end up as products.

Key Concepts:

  • Chemical reactions create new substances.
  • In a chemical reaction, the atoms and molecules that interact with each other are called reactants.
  • In a chemical reaction, the atoms and molecules produced by the reaction are called products.
  • In a chemical reaction, only the atoms present in the reactants can end up as products. No new atoms are created, and no atoms are destroyed.
  • In a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.

In an irreversible reaction, the reactants react to form the products, which cannot revert back into reactants. Irreversible reactions, as the reactants react with other reactants to form products, the products are reacting with other products to form reactants.

Reversible and irreversible reactions

Irreversible reactions
Generally we find that once reactants are converted into product then the product cannot be again converted into reactants. So, irreversible reactions are those reactions in which the products manufactured by reaction in reactants cannot be converted back in reactants.  These reactions are represented by putting single headed arrow ( ) between reactants and products.

For example, the cooking gas (L.P.G.) used in the kitchen is mainly butane gas, which on combustion with air produces carbon dioxide and water as products. 

C4H10 (g) + O2 (g)     CO2(g) + H2O (g) + Heat

In this reaction we cannot remanufacture butane using the carbon dioxide and water , so this is an irreversible reaction.

Reversible reactions
 In these reactions the products manufactured can be again converted into the reactants from which they are formed. These reactions are represented by putting a double headed arrow () between reactants and products. For example, 
       1) Nitrogen in gaseous form reacts with hydrogen gas to produce ammonia. This reaction can be shown as: 

N2 (g) +3H2 (g)    2NH3 (g)

It is seen that as when ammonia gas is produced in the above reaction it starts breaking into nitrogen gas and hydrogen gas immediately, in the reverse direction as given below:

2NH3 (g)    N2 (g) +3H2 (g)

Now because the reaction is taking place in both the directions i.e. in forward and in backward direction so we conclude that this reaction is reversible in nature, and it can be represented as:

N2 (g) +3H2 (g)    2NH3 (g)


Solubility is an ability of a substance to dissolve. In the process of dissolving, the substance which is being dissolved is called the solute and the substance in which the solute is dissolving is called the solvent. A mixture of solute and solvent is called a solution.

To simplify and explain, when you add and mix salt in water, then salt is the solute, water is the solvent and the resultant mixture is called solution.

Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent. The solubility of a substance is an entirely different property from the rate of solution, which is how fast it dissolves.

Some substances like alcohol and water can be mixed thoroughly and they are called miscible. Some substances like water and oil do not mix together and they are called immiscible substances.

Degree to which a substance dissolves in a solvent to make a solution  is called solubility.

Temperature has an impact on this, when you dissolve sugar or salt in hot water it will dissolve immediately.Thus solubility of solids in liquids increase with temperature and those of gases decrease with temperature and increase with pressure.

A solution in which no more solute can be dissolved at a given temperature and pressure is said to be a saturated solution.