On this page, you will find Matter in Our Surroundings Class 9 Notes Science Chapter 1 Pdf free download. CBSE NCERT Class 9 Science Notes Chapter 1 Matter in Our Surroundings will seemingly help them to revise the important concepts in less time.
CBSE Class 9 Science Chapter 1 Notes Matter in Our Surroundings
Matter in Our Surroundings Class 9 Notes Understanding the Lesson
1. Matter is everything around you. Everything in this universe is made up of material which in scientific term is called matter.
2. Matter can be defined as anything that occupies space possesses mass, offers resistance and can be felt by one or more of our senses.
3. Examples: Water, air, plant, animal, stones, clouds, etc.
Matter is classified on the basis of their physical and chemical nature.
- Physical classification: On the basis of physical properties, matter has been classified as solid, liquid and gas.
- Chemical classification: On the basis of chemical composition, matter has been classified as element, compound and mixture.
4. Properties of Matter
- Matter is made up of small particles.
- Particles of matter have space between them.
- Particles of matter are continuously moving.
- Particles of matter attract each other because of force of attraction.
5. States of Matter
This classification is done on the basis of arrangement among particles, energy of particles and the distance between the particles.
- They have fixed shape and definite volume.
- They have small interparticle distances.
- They are incompressible.
- They are rigid.
- They have high density and do not diffuse.
- They have strong intermolecular forces of attraction.
- Their constituent particles are very closely packed.
- Their kinetic energy is very less.
Examples: Sugar, salt, etc.
- They do not have fixed shape but have fixed volume.
- Their interparticle distances are larger than solids.
- They are almost incompressible.
- They have low density than solids.
- Their interparticle forces of attraction are weaker than solids.
- Their constituent particles are less closely packed.
- They assume the shape of the portion of the container they occupy.
- They can flow and thus can be called fluids.
- The kinetic energy of particles is more than that of solids.
- Examples: Milk, water, etc.
- They have neither fixed shape nor fixed volume.
- Their interparticle distances are largest among the three states of matter.
- They have high compressibility.
- They have least density and diffuse.
- Their interparticle forces of attraction are weakest.
- Their constituent particles are free to move about.
- They can expand to occupy larger volume.
- They are also called vapour.
- The particles of gases have maximum kinetic energy.
- Examples: H2, N2, CO2 etc.
6. Interchange of States of Matter
- Matter can be changed from one state to another state.
- Most of the metals, which are solid change into liquid on heating and then into vapour on further heating.
- The change of state of matter depends on:
7. Effect of Change of Temperature
8. The temperature effect on heating a solid varies depending on the nature of the solid and the conditions required for bringing the change.
9. Generally on heating, temperature of substances increases. But during state transformation, temperature remains same.
10. On heating: The kinetic energy of particles increases which overcomes the force of attraction between the particles thereby solid melts and is converted to a liquid.
11. Melting point: It is the temperature at which a solid changes to a liquid at atomospheric pressure.
12. Different substances have different melting points.
13. Higher the melting point means large forces of attraction between the particles.
14. Melting point of ice is 273.16 K.
15. The process of melting is also known as fusion.
16. Melting point is characteristic propertyof a substance.
17. Latent heat: The hidden heat which breaks the force of attraction between the molecule is called latent heat.
18. It is the heat supplied to a substance during the change of its state.
19. It is the heat energy hidden in the bulk of matter.
20. Latent heat of fusion: Amount of heat energy required to convert 1 kg of a solid into a liquid at atmospheric pressure at its melting point is known as latent heat of fusion of a substance.
21. A solid having stronger interparticle forces has greater latent heat of fusion.
22. Latent heat of fusion of water is 333.7 kJ/kg.
23. Boiling point: The temperature at which a liquid starts boiling at atmospheric pressure is known as its boiling point.
24. A liquid having weaker interparticle forces has lower boiling point and is more volatile.
25. Latent heat of vapourisation: The amount of heat energy required to convert 1 kg of a liquid into a gas at atmospheric pressure at its boiling point is known as latent heat of vapourisation of the substance.
26. Latent heat of vapourisation of water is 2259 kJ/kg. Thus 1 kg of water in the form of steam at 373 K has 2259 kJ more energy than 1 kg of water at 373 K.
27. Condensation: The change of state from gas to liquid is called condensation.
28. The condensation process is reverse of vapourisation.
29. Freezing: The change of state from liquid to solid is called freezing.
30. Freezing is the reverse of melting or fusion.
31. Sublimation: Sublimation involves direct conversion of a solid into the gaseous state on heating and vice-versa.
32. Dry ice sublimes at -78 °C (195 K).
33. Camphor, ammonium chloride, iodine and naphthalene are some substances which undergo sublimation.
34. Effect of Change of Pressure
In the gaseous state, the interparticle spaces are very large and attractive forces between the particles are negligible. Because of large interparticle space, gases are highly compressible. When pressure is applied on a gas, enclosed in a cylinder, its molecules move closer and the gas undergoes appreciable compression. As the molecules move closer, the attractive forces between the molecules increase. At a sufficiently high pressure, the gas changes into liquid.
(i) Solid CO2 is stored under high pressure. At a pressure of 1 atmosphere, solid CO2 changes directly into gas without passing through the liquid state. Solid CO2 is known as dry ice. Thus, we can conclude that we can liquefy gas by applying pressure and reducing temperature.
(ii) Change in volume from gaseous state to liquid state is very large whereas change in volume from liquid state to solid state is very small (negligible). This is due to the reason that in liquid the interparticle spaces are very small in a liquid.
(iii) Atmospheric pressure: The pressure exerted by the atmosphere or air is called atmospheric pressure. It decreases with increase in height.
(iv) Atmosphere (atm) is a unit of pressure.
(v) The SI unit of pressure is pascal (pa).
1 atm = 1.01 x 105pa
1 bar = 1 x 105 pa 1
bar = 1.01 atm.
(vi) Evaporation: The phenomenon of change of a liquid into vapour at any temperature below its boiling point is called evaporation.
(vii) Particles of matter possess kinetic energy. At a particular temperature, in a sample of liquid all the particles do not have same kinetic energy. There is a small fraction of molecule which has enough kinetic energy to overcome the attractive forces of other particles. If such a particle happens to come near the surface, it escapes into vapour state and evaporation takes place.
35. Factors Affecting the Rate of evaporation
(i) Surface area: Evaporation is a surface phenomenon, i.e., only the particles on the surface of the liquid gets converted into vapour. Thus, greater is the surface area, more is the rate of evaporation. For example, clothes dry faster when they are well spread out.
(ii) Increase in temperature: The rate of evaporation increases with increase in temperature. At higher temperature greater number of particles have enough kinetic energy to escape into the vapour state. For example, clothes dry faster in summer than in winter.
(iii) Decrease in humidity: The amount of water vapour present in air is referred to as humidity. The air cannot hold more than a definite amount of water vapour at a given temperature. If the humidity is more, the rate of evaporation decreases. For example, clothes do not dry easily during rainy season because the rate of evaporation is less due to high moisture content in the air.
(iv) Increase in the speed of the wind: 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. For example, wet clothes dry faster on a windy day.
(v) Nature of liquid: Different liquids have different rates of evaporation. A liquid having weaker interparticle attractive forces evaporates at a faster rate because less energy is required to overcome the attractive forces. For example, acetone evaporates faster than water.
(vi) Evaporation causes cooling: Only the liquid particles having high kinetic energy leave the surface of the liquid and get converted into vapour. As a result, the average kinetic energy of the remaining particles of the liquid decreases and hence the temperature falls. Thus, evaporation causes cooling.
Class 9 Science Chapter 1 Notes Important Terms
Melting Point: It is the temperature at which a solid changes into liquid at atmospheric pressure.
Freezing point: The temperature at which a liquid freezes to become a solid at atmospheric pressure is called the freezing point.
Boiling point: The temperature at which a liquid starts boiling at atmospheric pressure is called its boiling point.
Latent heat of vapourisation: The amount of heat energy that is required to change 1 kg of liquid into vapour at atmospheric pressure at its boiling point is called latent heat of vapourisation.
Condensation: The process of changing a gas (or vapour) to a liquid by cooling is called condensation. Sublimation: Sublimation involves direct conversion of a solid into the gaseous state on heating and vice-versa.
Latent heat: The hidden heat which breaks the force of attraction between the molecules is known as latent heat.
Latent heat of fusion: The heat of energy required to convert 1 kg of a solid into liquid at atmospheric pressure, as its melting point, is known as latent heat of fusion.
Boiling: Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.
Evaporation: Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the force of attraction present in the liquid and change into vapour state.