Class 9 : Important Points - Matter in our Surroundings Class 9 Notes | EduRev
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- Anything which occupies space and has mass is called matter.
- The matter is made up of small particles, which may be molecules, atoms or ions.
- The matter commonly exists in three states, i.e., solids, liquids and gases.
- The particles of matter are always in a state of motion and hence possess kinetic energy. The kinetic energy is minimum in solids, intermediate in liquids and maximum in gases.
Fig: Examples of matter
- The particles of matter attract each other with a force called intermolecular force, which is maximum in case of solids, less in case of liquids and least in case of gases.
- The spaces in between the particles of matter are called intermolecular spaces. They are least in case of solids, more in case of liquids and maximum in case of gases.
- The lesser the inter-molecular spaces between the molecules, the more are the intermolecular forces.
- In the case of solids, the intermolecular spaces and the kinetic energy of the molecules are the least, but the inter-molecular forces are maximum.
- In the case of liquids, the intermolecular spaces and the kinetic energy of the molecules are more than that in the solids, but the intermolecular forces are less than that in solids.
- In case of gases, the intermolecular spaces and the kinetic energy of the molecules are maximum, by the intermolecular forces are minimum.
- The arrangement of particles is most ordered in the case of solids, in the case of liquids layers of particles can slip and slide over each other while for gases, there is no order, particles just move about randomly.
- The states of matter are interconvertible and can be changed by changing the temperature and pressure.
Fig: Different states of matter
- Sublimation is the change of state from solid to gas, without going through liquid state on heating and vice versa.
- Fusion or melting is the change of state from solid to liquid and the temperature at which it takes place is called melting point.
- Vaporization or boiling is the change of state from liquid to gas and the temperature at which it takes place, is called boiling point.
- Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.
- Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapour state.
- The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed.
- Evaporation causes cooling.
- Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.
- Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.
- Density: The mass of a substance per unit of volume.
- Formula of density: mass/volume
- In SI unit is kgm-3
- Volume: All solids occupy a fixed volume. The shape occupied by a substance is called volume.
- The unit of volume is m3 (cubic meter). The common unit of volume is litre. (L)
1m3 = 1000 dm3 = 1000 L
1 L = 1 dm3
1 L = 1000 ml = 1000 cm3