You are aware that matter can exist in three physical states viz. solid, liquid and gas. Particles are held very close to each other in solids in an orderly fashion and there is not much freedom of movement. In liquids, the particles are close to each other but they can move around. However, in gases, the particles are far apart as compared to those present in solid or liquid states and their movement is easy and fast.
Because of such arrangement of particles, different states of matter exhibit the following characteristics:
- Solids have definite volume and definite shape.
- Liquids have definite volume but do not have definite shape. They take the shape of the container in which they are placed.
- Gases have neither definite volume nor definite shape. They completely occupy the space in the container in which they are placed.
These three states of matter are interconvertible by changing the conditions of temperature and pressure.
On heating, a solid usually changes to a liquid, and the liquid on further heating changes to gas (or vapour). In the reverse process, a gas on cooling liquifies to the liquid and the liquid on further cooling freezes to the solid.