These comprehensive RBSE Class 9 Science Notes Chapter 1 Matter in Our Surroundings will give a brief overview of all the concepts.
RBSE Class 9 Science Chapter 1 Notes Matter in Our Surroundings
→ Since early times, human beings have been trying to understand their nature. Earlier, matter was classified into five basic elements, the “Pancha Tattva”-Air, Earth, Fire, Sky and Water.
→ Matter : Anything that occupies space and has mass is called matter. For example –
Chair, table, cow, pencil, tree, etc.
→ Characteristics of Matter :
- Matter is made up of small particles. These small particles are called atoms.
- These atoms are too small, so they cannot be seen by naked eye.
- The atoms are constantly moving as they possess kinetic energy.
- These particles have inter-spaces between them.
- Particles of matter attract each other becausWe of force of attraction.
- Intermixing of particles of two different types of matter on their own is called diffusion.
→ Three states of Matter :
There are three states of matter –
Solid : Solids have fixed volume and shape. In solids, particles are closely packed and they have very less spacing between them. In solids, particles only vibrate at their mean position and they have less kinetic energy. The force of attraction between the particles of solids is very strong. For example – Stone, wood, sugar, coal, etc.
Liquid : Liquid has fixed volume but indefinite shape. In liquid, there is a weaker force of attraction and more spacing between the particles. In liquids, particles can move around and have high kinetic energy. For example – Milk, water, petrol, kerosene, etc.
Gas : Gases have indefinite shape and volume. Particles of gases have large space between them, but very weak attraction between them. Particles of gases move around very easily and have very high kinetic energy. For example – Air, hydrogen, nitrogen, etc.
→ Changes in states of Matter :
(i) Matter can be changed from one state to another state. A solid can be changed into . liquid and a liquid can be changed into gas.
(ii) Most of the metals, which are solid turn into liquid on heating and turn into vapour on further heating.
(iii) The change in states of matter mainly depends upon two factors :
→ Temperature : Generally, on heating temperature of substances increases. But, during the transformation, temperature remains the same.
→ Melting point : It is the temperature at which a solid changes into liquid.
→ Boiling point : It is the temperature at which a liquid changes into gas.
→ On heating –
(i) Temperature increases : When temperature increases, heat is used to increase the motion of the particles.
(ii) State changes : Particles use heat to overcome force of attraction to change the state.
→ Latent heat : It is the heat supplied to a substance during the change of its state.
(i) Latent heat of fusion : It is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.
(ii) Latent heat of vapourisation : It is the amount of heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.
(i) There is no effect of pressure on solids.
(ii) Solids are non-compressible.
(iii) When pressure increases on solid, it is deformed and finally broken.
(i) There is no effect of pressure on liquid.
(ii) Liquids are non-compressible.
(i) The volume of gas decreases with increase in pressure.
(ii) Since, there is lot of space between the particles of gas. Therefore, gas is compressible.
→ Evaporation : Evaporation is a phenomenon in which a liquid changes into vapour below its boiling point.
→ Factors Affecting Evaporation :
(ii) Surface area
→ Cooling Effect of Evaporation : Liquid needs latent heat of evaporation. It takes this heat from things in its surroundings. It means things in surroundings lose heat and thus they get cooled down.