Science class 9 chapter 1

Chapter 1

1.  Everything in this universe is made up of material which scientists have named “matter”. The air we breathe, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand – everything is matter. The things mentioned above occupy space and have mass. They have both mass* and volume**.

2. Early Indian philosophers classified matter in the form of five basic elements – the“Panch Tatva”– air, earth, fire, sky and water.

3. Modern day scientists have evolved two types of classification of matter based on theirphysical properties and chemical nature.

4. Matter is made up of particles.

5. When we dissolve salt in water, the particles of salt get into the spaces between particles of water.

6. A few crystals of potassium permanganate can colour a large volume of water (about 1000 L). there must be millions of tiny particles in just one crystal of potassium permanganate, which keep on dividing themselves into smaller and smaller particles.

7. Particles of one type of matter get into the spaces between particles of the other. This shows that there is enough

space between particles of matter.

8. Particles of matter are continuously moving, that is, they possess what we call the kinetic energy.

9. As the temperature rises, particles move faster. So, we can say that with increase in temperature the kinetic energy of

the particles also increases.

10. Particles of matter intermix on their own with each other. They do so by getting into the spaces between the particles. This intermixing of particles of two different types of matter on their own is called diffusion.

11. Particles of matter have force acting between them. This force keeps the particles together. The strength of this force

of attraction varies from one kind of matter to another.

12. We can see that matter around us exists in three different states– solid, liquid and gas. These states of matter arise due to the variation in the characteristics of the particles of matter.

13. All these have a definite shape, distinct boundaries and fixed volumes, that is, have negligible compressibility. Solids

have a tendency to maintain their shape when subjected to outside force. Solids may break under force but it is difficult to change their shape, so they are rigid.

14. Liquids have no fixed shape but have a fixed volume. Liquids flow and change shape, so they are not rigid but can be called fluid.

15. The gases from the atmosphere diffuse and dissolve in water. These gases, especially oxygen and carbon dioxide, are essential for the survival of aquatic animals and plants.

16. All living creatures need to breathe for survival. The aquatic animals can breathe under water due to the presence of dissolved oxygen in water.

17. Solids, liquids and gases can diffuse into liquids. The rate of diffusion of liquids is higher than that of solids. This is due to the fact that in the liquid state, particles move freely and have greater space between each other as compared to particles in the solid state.

18. Gases are highly compressible as compared to solids and liquids.

19. Compressed natural gas (CNG) is used as fuel these days in vehicles. Due to its high compressibility, large volumes of a gas can be compressed into a small cylinder and transported easily.

20. The particles of the aroma of food mix with the particles of air spread from the kitchen, reach us and even

farther away.

21. The smell of hot cooked food reaches us in seconds; compare this with the rate of diffusion of solids and liquids. Due to high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.

22. In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container.

23. Water can exist in three states of matter–

      • solid, as ice,

      • liquid, as the familiar water, and

      • gas, as water vapour.

24. On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed.

25. The melting point of ice is 273.16 K*. The process of melting, that is, change of solid state into liquid state is also known as fusion.

26. The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion.

27. Particles in water at 00 C (273 K) have more energy as compared to particles in ice at the same temperature.

28. The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point. Boiling is a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to change into the vapour state.

29. Particles in steam, that is, water vapour at 373 K (1000 C) have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporisation.

30. The state of matter can be changed into another state by changing the temperature.

31. Substances around us change state from solid to liquid and from liquid to gas on application of heat.

32. A change of state directly from solid to gas without changing into liquid state (or vice versa) is called sublimation.

33. The difference in various states of matter is due to the difference in the distances between the constituent particles.

34. Solid CO2 gets converted directly to gaseous state on decrease of pressure to 1 atmosphere*without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.

35. Pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas.

36. Particles of matter are always moving and are never at rest. there are particles with different amounts of

kinetic energy.

37. Phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.

38. Evaporation is a surface phenomenon. If the surface area is increased, the rate of evaporation increases.

39. Humidity is the amount of water vapour present in air. The amount of water in air is already high, the rate of evaporation decreases.

41. Clothes dry faster on a windy day. With the increase in wind speed, the particles of water vapour move away with the wind, decreasing the amount of water vapour in the surrounding.

42. People sprinkle water on the roof or open ground because the large latent heat of vaporisation of water helps to cool the hot surface.

43. During evaporation, the particles at the surface of the liquid gain energy from the surroundings or body surface and change into vapour. 
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