CHAPTER 3 PHYSICAL AND CHEMICAL CHANGES
Changes occurring around us can be broadly divided into physical and chemical changes.
PHYSICAL CHANGES
When a substance experiences a change in its physical properties like shape, size, colour or state, it is called physical change. Physical change does not form any new substance.
CHEMICAL CHANGES
When a substance undergoes a change in their chemical properties, it is called a chemical change. A chemical change is also called a chemical reaction and leads to the formation of new substances.
E.g. (i) Rusting of iron
The process of rusting is as follows:
Iron + Water + Oxygen → Rust
Fe + H2O + O2 → Fe2O3
When iron is left out in the open, a brownish film is formed over it. The brown film is called rust and this process is called rusting of iron.
To prevent rusting, iron is coated with a layer of zinc. This process is called galvanization.
(ii) Crystallization
A crystal of a substance is its pure solid form. Obtaining a substance in its pure form from its solution is called crystallization.
Depending on the changes, they may be classified into reversible or irreversible.
Changes occurring around us can be broadly divided into physical and chemical changes.
PHYSICAL CHANGES
When a substance experiences a change in its physical properties like shape, size, colour or state, it is called physical change. Physical change does not form any new substance.
CHEMICAL CHANGES
When a substance undergoes a change in their chemical properties, it is called a chemical change. A chemical change is also called a chemical reaction and leads to the formation of new substances.
E.g. (i) Rusting of iron
The process of rusting is as follows:
Iron + Water + Oxygen → Rust
Fe + H2O + O2 → Fe2O3
When iron is left out in the open, a brownish film is formed over it. The brown film is called rust and this process is called rusting of iron.
To prevent rusting, iron is coated with a layer of zinc. This process is called galvanization.
(ii) Crystallization
A crystal of a substance is its pure solid form. Obtaining a substance in its pure form from its solution is called crystallization.
Depending on the changes, they may be classified into reversible or irreversible.