Physical and chemical changes are two types of changes that occur. A physical change alters the physical properties of a substance but does not create new substances, while a chemical change produces new substances through a chemical reaction. Some key differences are that a physical change does not alter chemical properties, while a chemical change does. Examples of physical changes include freezing water to ice and stretching a rubber band. Chemical changes form new substances like rusting iron or reactions that produce carbon dioxide. Chemical reactions are represented by chemical equations that show the reactants and products.

1. CHAPTER NO:6
PHYSICAL AND CHEMICAL CHANGES :MODULE-1/1
BY
D.N.SESHADRI. AECS:KAIGA
CLASS:VII
SUBJECT:SCIENCE
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2. INTRODUCTION
PHYSICAL CHANGES (SECTION-A)
 Everyday we come across with some changes in our life and
in our surroundings as well .Our life is not static, it is dynamic,
as a consequence we could see many changes.
Broadly these changes are of two kinds, one is physical and
another one is chemical.
In this chapter we are learning the various aspects of physical
changes and chemical changes through definitions,
experiments ,activities, examples, etc.
The entire chapter is divided into two sections (Section –A and
Section-B) for convenient learning.
Now let us move on………………
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3. PHYSICAL CHANGES
Physical change :
A change in which
only physical
properties of any
substance change
and no new
substance is
formed is called a
physical change.
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4. CHARACTERISTICS OF
PHYSICAL CHNGES
The physical changes do not form a new substance(s).
The physical change do not change the chemical properties
of the substances(reactants) mixed for a physical change.
Eg : Freezing of water into ice , stretching of rubber band or
spring , attraction of iron filings by a magnet , recovery of
chalk from the chalk powder,etc.
Physical properties : Properties are such as shape,
size,colour and state of a substance are called physical
properties.
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5. CHEMICAL CHANGES
(SECTION-B)
A change in which two or more substances(reactants) combine
to produce one or more new substances(products) that has/have
different chemical properties than the reactants is called chemical
change. A chemical change is also known as chemical reaction.
Eg: 2H2 + O2→2H2O
In the above reaction the substances undergoing a chemical
reaction are called reactants , so H2 and O2are reactants: the
newly formed substance(s) as a result of a reaction are called
products, so H2O is the product.
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6. CHEMICAL REACTIONS
WITH CHEMICAL EQUATIONS
Magnesium + Oxygen
→ Magnesium oxide
Mg + O2 → MgO
Magnesium oxide + Water
→ Magnesium Hydroxide
MgO + H2O →Mg(OH) 2
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7. CHEMICAL REACTIONS
WITH CHEMICAL EQUATIONS
Copper sulphate
solution (blue) +
Iron→ Iron sulphate
solution (green) +
Copper (brown
deposit)
 CuSO4 + Fe→ Fe SO4 + Cu
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8. CHEMICAL REACTIONS
WITH CHEMICAL EQUATIONS
 Vinegar(acetic acid) + Baking
soda(sodium hydrogen
carbonate)→Carbon dioxide + other
substances . When this carbon
dioxide is passed through lime water
calcium carbonate is formed, which
makes the lime water milky.The
turning of lime water into milky is a
standard test of carbon dioxide.
Carbon dioxide(CO2) + Lime
water[Ca(OH)2] →Calcium
carbonate (CaCO3) + Water (H2O)
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9. IMPORTANT FEATURES ASSOCIATED WITH
CHEMICAL REACTIONS/CHEMICAL
CHANGES
Heat , light or any other radiation(ultraviolet)
may be given off or absorbed.
Sound may be produced.
A change in smell may take place or a new
smell may be given off.
A colour change may take place.
A gas may be formed.
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10. RUSTING OF IRON
If a piece of iron left in the open for some
time, it acquires a film of brownish
substance . This substance is called
rust.The process by which rust is formed
on an iron object is called rusting.For
rusting the presence of moisture(water
vapour) and oxygen are essential.
The process of rusting can be represented
by the following chemical equation:
Iron(Fe) + Oxygen(O2 from air) +
Moisture(H2O)→Rust(iron oxide Fe2O3)
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11. METHODS TO PREVENT RUSTING
❖ Deposit a layer of metal such as chromium or zinc on iron.
❖ The high content of moisture in air and higher contents of salts in water make the
process of rust formation faster.
❖ Stainless steel, a product of iron is made by mixing iron with carbon and metal su
nickel, chromium and manganese.Stainless steel does not rust.
❖ Galvanisation : The process of depositing a layer of zinc on iron is known as
galvanisation. The iron pipes are galvanised to prevent rusting.
❖ Electroplating is also done to avoid rusting.
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12. CRYSTALLISATION
❖Large crystals of
pure substances can
be obtained from
their concentrated
solutions, this
process of formation
of crystals is called
crystallisation.
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