Page 69 - Science Class 06

4. It is a reversible change. 4. It is an irreversible change.

5. No chemical reac on is involved in it. 5. Chemical reac on is permanent.

6. No change in the proper es of the 6. The substance loses its proper es
substance is involved. together.

1. Any irreversible change is also a permanent change. Why?
2. Give two examples of each reversible and irreversible change.

3. Moulding iron rod into iron sheet is a physical change. Why?
4. Give one example of chemical change from your day-to-day life.

ABSORPTION OR EVOLUTION OF ENERGY Endothermic Changes : The chemical

To carry out some reac ons the involve- changes in which heat energy is absorbed
are called endothermic changes.
ment of energy is a must. Plants absorb
energy from the sun and release water and Examples : Forma on of curd is intensified
carbon dioxide. This is also a chemical by heat, decomposi on of baking soda
change. On the other hand, on burning (Sodium bicarbonate) on hea ng and
wood or coal, heat energy is released. Thus, decomposi on of limestone (Calcium
on the basis of the involvement of bicarbonate) on hea ng.
energy, there are two types of changes—
exothermic and endothermic changes.

Exothermic Changes : The chemical
changes in which energy is released in the
form of heat or light are called exothermic

changes.
Conver ng of milk into curd is an example of
Examples : burning of coal, petrol, oil, endothermic reac on.
wood, natural gases, paper, etc. v A chemical reac on is a process in

which a substance is changed to a new
substance chemically. This happens
because the par cles of that subtance
undergo a change in their mutual

bonds.
v If two substances take part in chemical
reac on, they react with each other and
result in the forma on of a new
Exothermic reac on gives out energy. substance. The proper es of the new

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