Physical & Chemical changes

Physical changes

• A change in which a substance undergoes a change in its physical properties and now new substances are formed.
• It is temporary and generally reversible
• Only physical properties like size, shape, colour and state of matter changes.
• It may or may not be associated with energy change. Eg melting of ice/wax, magnetisation of iron, weathering. 

Chemical change

• A change in which one or more new substances with entirely different chemical composition and properties from the original substances are formed is called a chemical change.
• It is generally irreversible and permanent.
• Both the physical and chemical properties are changed. 
• Sound may be produced. 
• Heat, light or any other radiation may be given off or absorbed.     
• A colour change may take place.
• A change in odour may take place or a new odour may be given off. Eg burning of fuel, burning of food, baking of cake, digestion of food, rusting of iron.

Rusting

When iron objects are kept in moist air, a brown coating of iron oxide is formed.