CBSE – 10th Standard Science

Rs. 499.00

Class 10 Chapter 1 – Chemical Reactions and Equations

A complete chemical equation represents the reactants, products and their physical

states symbolically.

>A chemical equation is balanced so that the numbers of atoms of each type involved

in a chemical reaction are the same on the reactant and product sides of the

equation. Equations must always be balanced.

Fe + H2O —> Fe3O4 + H2                       (unbalanced equation)

3Fe + 4H2O —>Fe3O4 + 4H2                (balanced equation)

The balanced Eq. becomes

3Fe(s) + 4H2O(g) —> Fe3O4(s) + 4H2(g)

Sometimes the reaction conditions, such as temperature, pressure, catalyst, etc., for the reaction are indicated above and/or below the arrow in the equation

image001

TYPES OF CHEMICAL REACTIONS—

>In a combination reaction two or more substances combine to form a new single substance.

image002

Formation of water from H2(g) and O2(g)

 2H2(g) + O2(g) —> 2H2O(l)

Decomposition reactions are opposite to combination reactions. In a decomposition reaction, a single substance decomposes to give two or more substances.

image003

white silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride into silver and chlorine by light.

2AgCl(s) —>2Ag(s) + Cl2(g)

Silver bromide also behaves in the same way.

2AgBr(s) —>2Ag(s) + Br2(g)

The above reactions are used in black and white photography.

Reactions in which heat is given out along with the products are called exothermic  reactions.

examples of exothermic reactions are –

 Burning of natural gas

CH4(g) + 2O2 (g) —> CO2 (g) + 2H2O (g)

Reactions in which energy is absorbed are known as endothermic reactions.

>When an element displaces another element from its compound, a displacement reaction occurs.

image004

>Two different atoms or groups of atoms (ions) are exchanged in double displacement reactions

image005

image006

>Precipitation reactions produce insoluble salts

The chemical reaction in which a white coloured substance which is insoluble in water (precipitate) is formed then it is known as precipitation reaction

image007

In this reaction Barium sulphate is a white colour precipitate and it is insoluble in water.

Oxidation is the gain of oxygen or loss of hydrogen

image008

Reduction is the loss of oxygen or gain of hydrogen

image009

image010

CORROSION

image011

RANCIDITY

 image012

Course Curriculum