Physical and Chemical Changes of Materials

There are some changes during which no new substances are formed. On the other hand, there are some other changes during which new substances are formed. So, on the basis of whether new substances are formed or not, we can classify all the changes into two groups: 

(i) Physical changes (ii) Chemical changes

1.0Physical Changes

Those changes in which no new substances are formed, are called physical changes. In a physical change the substances involved do not change their identity. The changes in physical state, size and shape of substances are called physical changes. 

When ice is heated, it melts to form water. Though ice and water look different, they are both made of water molecules. Thus, no new chemical substance is formed during the melting of ice. So, the melting of ice to form water is a physical change.

When water is cooled, it solidifies to form ice. This is called freezing of water. The freezing of water to form ice is also a physical change.

Some other examples of physical changes are: Boiling of water, condensation of steam and breaking of a glass.

2.0Chemical Changes

Those changes in which new substances are formed are called chemical changes.

In a chemical change, the substances involved change their identity. They get converted into entirely new substances. 

For example,

When a magnesium wire is heated, it burns in air to form a white powder called 'magnesium oxide'. This magnesium oxide is an entirely new substance. Thus, a new chemical substance is formed during the burning of a magnesium wire. This is a chemical change.

Some other examples of chemical changes are: Burning of candle and burning of hydrogen in oxygen to form water.