World of Matter – Maharashtra Board Class 9 Solutions for Science and Technology (English Medium)
- Camphor and naphthalene are sublimatory substances.
- On heating, solids get converted to liquids and liquids get converted to gases.
- We usually find matter in solid, liquid and gaseous forms.
Substances which are lighter in weight float. The density of ice is less than that of water. Hence, ice floats on water.
In solids, the particles are very closely packed. Also, the force of attraction between the particles is very strong. They cannot move away from each other. Hence, solids have a definite shape.
A gas is liquefied by lowering its temperature below a particular temperature, which is characteristic for the given gas and then applying high pressure.
- In the gaseous state, particles move with random motion at high speed. So, these particles collide with the walls of the container and with each other too.
- Force per unit area is known as pressure. Thus, they exert force on the walls of the container.
- Therefore, gas exerts pressure on the walls of the closed container.
As compared to solids and liquids, gases are highly compressible. So, a large volume of gas can be compressed into a small cylinder and easily transported to the places where it is used as a fuel for vehicles and cooking. Hence, in the LPG cylinder, the gas filled is in the liquefied state.
- At 257°C, water is in the gaseous state in the form of steam.
- At 100°C, water gets converted to the gaseous state if heat is supplied continuously.
- At 0°C, water gets converted to the solid state, i.e. ice, provided heat is removed from it.
- Particles of matter are continuously moving. They possess kinetic energy.
- The smell of food reaches us because of the process of diffusion of the aroma of the particles of food into the air.
- As the temperature raises, the kinetic energy of particles raises and the rate of diffusion also rises.
- Thus, we get the smell of hot food several metres away, but to get the smell of cold food, we have to go close to it.