A physical change alters a substance's physical properties like shape, size, or state, but does not create new substances. A chemical change produces new substances through chemical reactions, altering both physical and chemical properties. Some key differences are that physical changes are typically reversible without new substances forming, while chemical changes are permanent reactions that form new substances through energy absorption or release. Rusting of iron is a chemical change that occurs when iron reacts with oxygen and water in the air, forming hydrated iron oxide (rust) which damages the iron over time.

1. PHYSICAL AND CHEMICAL CHANGE

2. CHANGES AROUND US.

3. PHYSICAL CHANGE.
If we find any difference in shape, size,
colour and state of a substance we say its a
physical change. A change, in which only the
physical properties of any substance get
changed and no new substance is formed, is
called a physical change.

4. EXAMPLES OF PHYSICAL CHANGE
Formation of Clouds Melting of Ice
Melting of ice
•Grinding of a substances.
•Magnetisation of a piece of
Iron.
•Stretching of a rubber band.

5. Characteristics of Physical Changes
During a physical change, only physical
properties(such as size, shape, colour and
state)changes.
During a physical change, no new substances is
formed.
A physical change can be either reversible or
irreversible(Dissolving sugar in water is a
reversible change).
No very small amount of energy is either
absorbed or evolved during a physical change.

6. CHEMICAL CHANGE
A change in which composition and
chemical properties of substance are
changed and formed, is called Chemical
change.

7. EXAMPLES OF CHEMICAL CHANGE
Burning of incense stick Burning of coal
Rusting of iron
•Spoilage of food
•Digestion of food
•Burning of dry leaves
•Explosion of fireworks

8. Characteristics of Chemical Changes
During a chemical change, one or more new substance
are formed.
Chemical changes are permanent. Thus, a chemical
change cannot be reversed by simple physical methods.
During a chemical change, relatively larger amount of
heat, light or any other radiation may be given out or
absorbed.
During a chemical change, both the physical and
chemical properties of a substance are changed.

9. Difference Between Physical and
Chemical Change
S.No. Parameters Physical change Chemical change
1 New substance No new substance is
formed.
One or more substance are
formed.
2 Nature of change It is a temporary change. It is a permanent change.
3 Reversibility It is reversible by simple
physical methods.
It is irreversible.
4 Physical and
chemical properties
Only physical substance are
changed.
Both physical and chemical
properties of substance are
changed.
5 Amount of energy(in
the form of heat,
light, etc.)
Very little amount of energy
is absorbed or given out.
A very large amount of
energy is absorbed or given
out.

10. RUSTING OF IRON
Iron objects like iron nails, iron pipes, iron
grills and iron railings, when kept in moist air
for a few days, get covered with powdery
substance called rust. This process is called
rusting of iron.
The two conditions, necessary for the rusting
of the iron are:
 Presence of oxygen(of air)
Presence of water or water
vapour(moisture)

11. Iron combines with the oxygen (of air) in the
presence of water (or moisture) to form hydrated
iron hydroxide.
This hydrated iron hydroxide is called rust.
IRON(METAL)
(DAMPED AIR)
OXYGEN+WATE
R
HYDRATED
IRON
OXIDE(RUST:R
ED-BROWN)

12. Rust is soft and porous. The layer of rust
formed falls of from the surface, exposing
fresh iron which starts rusting. This continues
rusting makes the iron weak and ultimately
useless.
Iron is the cheapest& most easily available
metal. Rusting causes a great loss & damage.
It is an irreversible chemical change
RUSTING DAMAGES IRON OBJECT

13. PREVENTION OF RUSTING
1.Coating the iron surface with paint or grease.
2.Coating iron with other metals(Galvanisation):
The process of depositing a thin layer(coating) of
zinc metal on iron object is called galvanisation.
3.By converting iron into stainless steal: Molten
iron consist of carbon, chromium and nickel. On
cooling, it forms an alloy called stainless steal. The
stainless steal does not rust at all in moist air

14. CRYSTALLISATION
The salt obtained from the sea water by the
process of evaporation is not pure and its crystals
are very small and shape cannot be seen clearly.
Crystals are the purest solid form of a substance
with a definite geometrical shape. Crystals of
different substances have different shape. Large
crystals of pure substances can be easily form
their saturated solutions by the process of
crystallisation. By obtaining crystals, we are able
to purify certain substances.