Changes around us

PHYSICAL AND CHEMICAL CHANGES

All changes which we see can be broadly divided into Physical changes and chemical changes.

Physical changes: Some changes affect only physical properties of the substances that is undergoing change, physical properties include size, shape and state of matter.

Some properties of physical change:

a) A physical change is temporary change.

b) No new substances is formed when physical change takes place.

c) A physical change generally reversible.

Chemical changes: Chemical changes are in the form of chemical reactions, which lead to the formation of new substances.

Some properties of chemical change:

a) Chemical change is permanent.

b) A new substance is formed.

c) A chemical change is generally irreversible.

Example for physical and chemical change:- Crystallisation : It is physical change, since the process involves a change in the state of matter. No new substance is created in the process of Crystallisation.

Galvanisation: The rusting of iron can be prevented by coating iron with something else such as paint or with zinc through a process called Galvanisation.

Rusting :If articles made of iron are kept in open air for some time,they get coated with o brown powdery substance called RUST. It is example for chemical change.The process of Rusting can be represented as:Fe + O2 (from air) + H2O->Fe2O3 (Rust).No rusting occurs if iron reacts only with water or air.

Some methods to prevent rusting are:

a) Oiling and greasing.

b) Coating with other metals.

c) Converting iron into stainless steel.