Chemical Reaction and Chemical Equation.


Chemical Reaction and Chemical Equation.

Chemical Reaction and Chemical Equation. Many changes are seen all around us in daily life, like the formation of water due to the melting of ice, the formation of steam from water, the burning of bulbs and candles, the formation of curd from milk, etc. You may have seen some interesting events in these changes, like, if the vegetable stains on clothes while eating, then the yellow stain of turmeric becomes red after applying soap.

Similarly, when you cut an apple to eat, it also turns red in a short time, iron nail rusts on it, a green layer appears in the rain on the copper vessel and gives red color when green henna is formed, etc.

Do also see the magic of some spectacles, how it fires a plate full of water with a sprinkler. You will have a lot of fun and wonder how he fires in the water. When he pours one glass solution into another glass, how does the deep white smoke come out? There are many events, and many changes that we see.

Some of these changes are permanent and after some changes, the substance reverts to its predecessor. That is, in a change, only the change in physical state is physicochemical and in a change, a completely new substance becomes a change. There are two types of changes on this basis.

Changes in which only the physical properties of substances change, and no new substance is formed, it is called “Physical Change”. These changes are temporary and irreversible, that is, after some time the substance can come back to its former state. Such as the melting of ice, formation of steam from water, lightning of the bulb, turning of the substance into powder, and dissolving of sugar, and salt in water.

The changes in which a substance basically changes into a new substance, that is, the chemical composition of the substance changes, is called a chemical change. These changes are permanent and irreversible, that is, after the change, the substance is not able to return to its former state.

Such as the formation of curd of milk, burning of candles, digestion of food, rusting of iron, etc. The process in which substances interact and form new substances, whose properties are different from the properties of the substances that act, is called a chemical reaction.

Chemical reactions in which heat is emitted are called exothermic reactions and in which heat is absorbed, endothermic reactions are called endothermic reactions.


  1. You know that plants make their food through the process of photosynthesis. In this process, they absorb the heat of the sun. Thus the process of photosynthesis is also an endothermic process.
  2. Similarly, heating sodium bicarbonate (eating soda) is also an endothermic process.

By doing the above symptoms in chemical reactions, we found out that chemical reactions have the following important characteristics:

(1) Phase change (Activity-1)

(2) release of gas (Activity-2)

(3) Color change (Activity-3)

(4) Energy conversion (emission or absorption of heat) (Activity-4)

Chemical Equation

Now you have understood chemical changes and chemical reactions very well, but when we have to display these reactions briefly, then we write it as an equation which is called a chemical equation.

How to write chemical equations:

The important terms of writing any chemical equation are as follows:

(i) The reactive substance is written on the left and the producing substances are on the right.

As nitrogen and hydrogen make ammonia, here nitrogen and hydrogen are reactants and ammonia products, hence:

(ii) The direction of the chemical reaction is shown by placing the arrow symbol forward between the reactant and the producing material. The sign = is also used somewhere in place of an arrow.

(iii) The conditions required for the reaction are shown above the arrow mark.


(iv) The physical states of the reactants and products are indicated by (g), (l), (s), and (aq) signals.


g = gas

l = liquid

s = solid

aq = aqueous (aqueous solution)

(v) Gaseous products are directly represented by arrows (↑) and solid products (precipitates) are shown with inverted arrows (↓).


Thus each chemical reaction is represented by a chemical equation. Chemical equations are, in fact, a short method of representing a reaction by chemical signals and formulas.