Wed. Jul 6th, 2022

# Chemical Reactions and Equations Class 10 Notes Science Chapter 1

Apr 29, 2022

## 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)

b)

## Endothermic Reaction:

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

## 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:

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.

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: