This document discusses physical and chemical changes. It defines physical changes as changes where a substance undergoes change without forming a new substance, and chemical changes as changes where new substances are formed. It provides examples like heating water and melting butter as physical changes, and cooking food and lighting a match as chemical changes. The document also discusses the rusting of iron as a chemical change, outlining factors that affect rusting like moisture, acid, salt, and impurities. It describes galvanization and using stainless steel as ways to prevent rusting of iron. Finally, it briefly discusses crystallization as a physical change involving deriving crystals from solutions.

1. PHYSICAL AND CHEMICAL
CHANGES
BY
SHAURYA

2. WHAT ARE CHANGES ?
 Changes occur around us all the time. Milk turns
sour, seed germinate, the weather changes and
fruit ripen.
Changes can be of different types: desirable and
undesirable changes, slow and fast changes,
temporary and permanent changes, reversible and
Irreversible changes and physical and chemical
changes.
All these changes involve one or more substances.
Each substance has a unique composition.

3. WHAT ARE PHYSICAL CHANGES ?
 Physical changes: When a substance undergoes a physical
change, it does not give rise to a different kind of substance
or there is no new substance is formed. A physical change is a
reversible change.
For example; heating of water melting of butter, folding of
paper etc.


4. WHAT ARE CHEMICAL CHANGES?
 Chemical changes: A Chemical change occurs when two or more
chemical substances react to form new product that have an entirely
different set of properties. A chemical change is mostly Irreversible.
For example; cooking food, ripening of fruit, lighting a matchstick,
aging of leaves and digestion of food etc.

5. DIFFERENCE BETWEEN PHYSICAL
AND CHEMICAL CHANGES:

6. RUSTING OF IRON:
 We all must have observed newly bought iron, a silver or copper
article appears very shiny but with passage of time they get dull.
This is due to the layer of metal oxide that develops on their surface.
Rusting of iron, silver jewellery getting tarnished or copper articles
getting covered by green layer. Metals react with atmospheric
oxygen and produces metal oxides that are basic in nature because
they react with water to form bases.
 In case of rusting of iron, the iron reacts with the oxygen present in
air and moisture and develops rust (hydrated iron (III) oxide).

7. FACTORS THAT AFFECT THE
RUSTING OF IRON:
 Many factors speed up the rusting of iron, such as the moisture
content in the environment and the pH of the surrounding area.
Some of these factors are listed below.
 Moisture: The corrosion of iron is limited to the availability of water
in the environment. Exposure to rains is the most common reason
for rusting.
 Acid: if the pH of the environment surrounding the metal is low,
the rusting process is quickened. The rusting of iron speeds up when
it is exposed to acid rains. Higher pH inhibits the corrosion of iron.
 Salt: Iron tends to rust faster in the sea, due to the presence of
various salts. Saltwater contains many ions that speed up the
rusting process via electrochemical reactions.
 Impurity: Pure iron tends to rust more slowly when compared to
iron containing a mixture of metals.

8. PREVENTION OF RUSTING OF
IRON:GALVANISATION
 So, how do we prevent rusting? Prevent iron articles from coming in contact with
oxygen, or water, or both. One simple way is to apply a coat of paint or grease. In
fact, these coats should be applied regularly to prevent rusting. Another way is to
deposit a layer of a metal like chromium or zinc on iron. This process of depositing a
layer of zinc on iron is called galvanisation. The iron pipes we use in our homes to carry
water are galvanised to prevent rusting.
 You know that ships are made of iron and a part of them remains under water. On
the part above water also water drops keep clinging to the ship’s outer surface.
Moreover, the water of the sea contains many salts. The salt water makes the process
of rust formation faster. Therefore, ships suffer a lot of damage from rusting in spite of
being
 Stainless steel is made by mixing iron with carbon and metals like chromium, nickel
and manganese. It does not rust.
 painted. So much so, that a fraction of ship’s iron has to be replaced every year.

9. CRYSTALLISATION:
 The process of deriving large crystals of pure substances from their
solutions is known as crystallisation. It is a physical change. Crystals
of salt are obtained by the evaporation of sea water.
 Similarly crystals of copper sulphate can be obtained by adding
copper sulphate powder to the boiling solution of water and dilute
sulphuric acid. This mixture when filtered and allowed to cool
produces crystals of copper sulphate.

10. THANKYOU