4th Class Science Matter and Materials Physical and Chemical Change

     Physical Change

Physical change is the change in which a substance undergoes the change in its physical properties (shape, size, colour or the state of a substance). A physical change is only a temporary change. This change can be reversed. For example tear a page from your note book into 4 square pieces. Now lay these pieces on the table in such a manner that it occupies the shape of the original piece of paper. The physical change, brought about by tearing the paper, is back by putting it in order. There is no change in the property of the paper.

Change in states of water (physical change)    

        Chemical Change

A chemical change is the change is which new substances are formed and the original substance can't be get back. The change Is permanent. For example burning of a cracker is a chemical change in which heat, sound, light and gases are produced and we cannot get back crackers.

Burning of a cracker (chemical change)  

     Coconut oil in winter solidifies. We leave it in the sunlight and it liquefies again. This type of change in property is called.

(a) No change

(b) Chemical change

(c) Physical change 

(d) Both B and C

(e) None of the above

Answer: (c)

     Iron gate of a park is exposed to moist air. It gets rusted. Can you name the type of change?

(a) Chemical change

(b) Reversible change

(c) Physical change

(d) All of the above

(e) None of the above

Answer: (a)

It is believed that an atom is made of 200 or more than 200 subatomic particles.

A human hair is about 1 million carbon atoms.

A speck of dust might contain 3 trillion atoms.

Atom: Smallest particle of an element.

Molecule: A molecule is defined as a group of at least two atoms.

States of Matter: Matter exist in three different states.

Physical Change: Change in physical property.

Chemical Change: Change in chemical property.