Chemical reaction and Equation| Important Notes

chemical reaction and equation
chemical reaction and equation

Today we shall discuss a very important lesson Chemical reaction and Equation.we shall get the knowledge about important terms and concept. we shall learn how to balance chemical equtaion.

⚫What is chemical reaction?

Chemical reactions happen only when there is chemical change occur throughout the process.


👉 Digestion of food

👉 Milk into curd

⚫What is chemical equation?

Chemical reaction can be expressed symbolically by using the chemical equation.

For example:

Aqueous solution of copper sulphate + zinc dust ➡️ equation of zinc sulphate + copper

This can be represented symbolically,


⚫What is balance chemical equation?

Balance equations are those equations in which the number of atoms of each elements present in the reactions remain same as the reactant and product side.


2Ag(s)+2HCl(g) ➡️ 2AgCl(ppt)+H2(g)

SO2(g)+H2S(l) ➡️ S(s)+H2O(l)

⚫ Type of chemical reactions

👉 What is combination reaction?

When two or more reactants combine in a reaction to form a single product it is known as a combination reaction.


NH3(g)+HCl(g) ➡️ NH4Cl(s)

2Mg(s)+H2O(l) ➡️ 2MgO(s)

👉 What is decomposition reaction?

In this type of reaction two or more products are formed from a single reactant. It is just opposite to the combination reaction.

There are basically three types of 

decomposition reaction

◾Thermal decomposition

Under this decomposition heating is required.


CaCO3(s)+heat ➡️ CaO(s)+CO2(g)

◾Electrolytic decomposition

When a decomposition reaction is carried out by electric current.


H2O(l) ➡️ H2(g)+O2(g)

◾Photolytic decomposition

 this type of decomposition is done with the help of light.


AgCl(s) ➡️ Ag(s)+Cl2(g)

👉 Displacement reaction

In this type of reactions an element displaces another element from its solution.


Fe(s)+CuSO4(aq) ➡️ FeSO4(aq)+Cu(s)

Pb(s)+CuSO4(aq) ➡️ PbSO4(aq)+Pb(s)

👉 Double displacement reaction

The reaction in which ions in the reactants are exchanged to form a precipitate are called double displacement reaction.


Na2SO4(aq)+BaCl2(aq) ➡️ BaSO4(s)+NaCl(aq)

⚫ Some other type of reactions are as follows

👉 Exothermic reaction

This type of reaction heat is given out along with the formation of product.


CaO(s)+H2O ➡️ Ca(OH)2+ऊष्मा

👉 Endothermic reaction

In this type of reactions heat is absorbed during the reaction.


CaCO3(s)+ऊष्मा ➡️ CaO(s)+CO2(g)

chemical reaction and equation
chemical reaction and equation

👉 Oxidation and reduction reaction

When oxygen is added to an element the reaction is known as oxidation.

C(s)+O2(g) ➡️ CO2(g)

When hydrogen is added to an element the reaction is called as reduction.

2H2(g)+C(s) ➡️ CH4(g)

👉 Redox reaction

When in any reaction oxidation and reduction take place simultaneously the reaction is known as redox reaction.

Redox reaction = reduction + oxidation

⚫What is corrosion?

When a metal is attacked by substance around it such as moisture and a seed it get degraded. This process is called as corrosion.


👉 Black coating on silver

👉 Reddish brown coating on iron

Chemical formulae for rust Fe2O3.xH2O

⚫What is rancidity?

When fats and oils are oxidised they become rancid and their smell and taste changes.

Rancidity in the food stuff cooked in the oil or ghee is prevented by using antioxidants.

The process of oxidation reaction of food stuff can also be slowed down by storing in airtight container.

⚫How to write a chemical equation?

👉 Reactants are always written on the left side And Products are always written on the right side

👉 Between reactants and products arrow ( ➡️ )sign is placed between reactants and products.

👉 When two reactants are there in the reactan sidet then Plus sign is placed between them.

👉 Similarly when there are two products in product side the Plus sign is placed between them.

👉 In particular case of reaction to show temperature, pressure and catalyst they are written on the arrow.

👉 Delta symbol is placed on arrow to represent heating process.

👉 Physical states like solid, liquid, gases are written in the bracket below the elements present in the reactant side and product side.

👉 If the gas is given out, upward Arrow is represented.

And if the precipitate is formed, downward Arrow is placed.

⚫What are the factors affecting the rate of reaction?

👉 Nature of reactants

Nature of the metal is responsible for the rate of reaction. For example Aluminium is more reactive compared to the Zinc with hydrochloric acid.

👉 Size of particle of reactants

The rate of reaction depends upon the size of the particle of the reactants taking part in the reaction smaller the size of reactant particle higher is the rate of reaction.

👉 Concentration of reactants

If the reactant is concentrated its reaction will be more faster.

Reaction of dilute acid with calcium carbonate is slow while the reaction of concentrated acid with calcium carbonate is faster.

👉 Temperature of the reaction

Rate of the reaction increases while increasing the temperature of the reaction and decreases while decreasing the temperature of reaction

👉 Catalyst

Catalyst are those substances which increases the rate of reaction without reacting during the course of reaction

⚫Some key points

👉 The chemical reactions are profitable in the chemical factories if the rate is fast.

👉 In our body in genes increases the rate of physiological reactions.

👉 Some chemical reactions occur at faster speed why some occur at the slower speed and some occur at the moderate speed.

👉 Strong acid and strong base react very fast.

👉 The ozone layer in the earth atmosphere protect the life on the earth from ultraviolet radiation of the Sun. The process of depletion or maintenance of these layer depends upon the rate of production or destruction of ozone molecules.

7th PAY COMMISSION | DA में  बढ़ोतरी2022

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Metals & nonmetals

Reflection of light

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