Wed. Jul 6th, 2022
Chemical Reactions and Equations Class 10 Notes Science Chapter 1

Chemical Reactions and Equations Class 10 Notes Science Chapter 1

Chemical Reaction: 

The transformation of a chemical substance into another chemical substance is known as Chemical Reaction.

For example: Rusting of iron, the setting of milk into curd, digestion of food, respiration, etc.

Chemical Equation: 

The representation of a chemical reaction using symbols and formulae of the substances is called a chemical equation.

Combination Reaction: 

Reactions in which two or more reactants combine to form one product are called combination reactions.

A general combination reaction can be represented by the chemical equation given here:
A + B → AB

Examples:

a) Mg(s) + O2(g) → 2MgO(s)

b) C (s) + O2(g) → CO2(g)

Decomposition Reaction: 

Reactions in which one compound decomposes in two or more compounds or elements are known as decomposition reactions.

A general decomposition reaction can be represented as follows :
AB → A + B

Examples:

a) CaCO3 → CaO + CO2

b) 2H2O→ 2H2 + O2

Thermal Decomposition: 

The decomposition of a substance on heating is known as thermal decomposition.

Example:

CaCO3 → CaO + CO2

Electrolytic Decomposition: 

Reactions in which compounds decompose into simpler compounds because of the passing of electricity are known as electrolytic decomposition.

This is also known as Electrolysis.

Example:

2H2O→ 2H2 + O2

Photolysis or Photo Decomposition Reaction: 

Reactions in which a compound decomposes because of sunlight are known as Photolysis or Photo decomposition reactions.

Example:

2AgCl → 2Ag + Cl2

Displacement Reaction: 

The chemical reactions in which a more reactive element displaces a less reactive element from a compound are known as displacement reactions.

Displacement reactions are also known as Substitution Reactions or Single Displacement/ replacement reactions.

A general displacement reaction can be represented by using a chemical equation as follows :
A + BC → AC + B

Examples:

a) Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

b) Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

Double Displacement Reaction: 

Reactions in which ions are exchanged between two reactants forming new compounds are called double displacement reactions.
AB + CD → AD + CB
Examples:
a) BaCl2(aq) + Na2SO4(aq) → BaSO4(s) (Precipitate) + 2NaCl(aq)

b) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Oxidation: 

Addition of oxygen or removal of hydrogen from a compound is known as oxidation.

Reduction: 

Addition of hydrogen or removal of oxygen from a compound is called reduction.

Oxidizing agent:

The substance which gives oxygen or removes hydrogen for oxidation is also called an oxidizing agent.

Reducing agent:

The substance which gives hydrogen or removes oxygen for reduction is called a reducing agent.

Exothermic Reaction: 

A chemical reaction in which heat energy is evolved is called an exothermic reaction.

Example:
a)

Chemical Reactions and Equations Class 10 Notes Science Chapter 1 3

b)

Chemical Reactions and Equations Class 10 Notes Science Chapter 1 4


Endothermic Reaction: 

A chemical reaction in which heat energy is absorbed is called an endothermic reaction.
Example:

Chemical Reactions and Equations Class 10 Notes Science Chapter 1 5

Corrosion: 

The process of slow conversion of metals into their undesirable compounds due to their reaction with oxygen, water, acids, gases, etc. present in the atmosphere is called corrosion.
Example: Rusting of iron.

Rancidity

The taste and smell of food materials containing fat and oil change when they are left exposed to air for a long time. This is called rancidity.

It is caused due to the oxidation of fat and oil present in food materials.

Methods to prevent rancidity:

a) By adding anti-oxidant.

b) Vacuum packing.

c) Replacing air by nitrogen.

d) Refrigeration of foodstuff.

Rusting: 

Iron when reacts with oxygen and moisture forms a new substance which is called rust. The process involved is called rusting.
Chemical Reactions and Equations Class 10 Notes Science Chapter 1 6

Methods to Prevent Rusting

a) By painting.

b) By greasing and oiling.

c) By galvanization.

Q. Name the type of chemical reaction represented by the following equation:

chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-3

Answer.
(i) Combination reaction
(ii) Double displacement reaction (Precipitation reaction)
(iii) Decomposition reaction.

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