CBSE Class 9 Science Matter in our sorroundings Notes

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All matters in the universe exist in three states. There are two ways of classification of matter.

1. According to physical state as solid, liquid or gas.

2. According to its composition as element, compound or mixture.

CHARACTERISTICS OF PARTICLES OF MATTER

PARTICLES OF MATTER HAVE SPACE BETWEEN THEM- when we make tea, coffee or lemonade (nimbu paani ), 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. Similarly particles of sugar, salt, Dettol, or potassium permanganate get evenly distributed in water.

PARTICLES OF MATTER ARE CONTINUOUSLY MOVING- Particles of matter are continuously moving, that is, they possess what we call the kinetic energy. As the temperaturerises, particles move faster. So, we can say that with increase in temperature the kinetic energ of the particles also increases.

PARTICLES OF MATTER ATTRACT EACH OTHER- 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.

INTEXT QUESTIONS 

Q1. Which of the following are matter? Chair, air, love, smell, hate, almonds, thought, cold, colddrink, smell of perfume.

Answer: Chair, air, smell, almonds, cold-drink and smell of perfume are matter because they have some weight and occupy space.

Q2. Give reasons for the following observation:

The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.

Answer: Hot food evaporates easily. Its vapours diffuse between the air molecules and reach within a short time to a distant place. But the case is different with the cold food because it remains in solid form and does not mix with air molecules, so we have to go close to smell it.

Q3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Answer: The phenomena of cutting the water by the diver show that matter has space between its particles.

Q4. What are the characteristics of the particles of matter?

Answer: Characteristics of particles of matter :

1. Particles of matter have space between them.

2. Particles of matter are continuously moving.

3. Particles of matter have an attraction force between them.

4. Particles of matter are very small in size.

STATES OF MATTER

1. THE SOLID STATE- all solids 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.

2. THE LIQUID STATE- Liquids have no fixed shape but have a fixed volume. They take upthe shape of the container in which they are kept. Liquids flow and change shape, so they are not rigid but can be called fluid. 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 spacebetween each other as compared to particles in the solid state.

3. THE GASEOUS STATE- Gases are highly compressible as compared to solids and liquids. The liquefied petroleum gas (LPG) cylinder that we get in our home for cooking or the oxygensupplied to hospitals in cylinders is compressed gas. 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.

INTEXT QUESTIONS PAGE NO. 6

Q1. The mass per unit volume of a substance is called density. (density = mass/volume). Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron.

Answer: The order of density is gas< liquid< solid. Thus,

Q2. (a) Tabulate the differences in the characteristics of states of matter.

Answer:(a) The differences in the characteristics of states of matter are given in the following table.

(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.

Answer:

(i) Rigidity The property due to which an object retains its shape and size is known as rigidity. Solids are rigid whereas liquids and gases are not.

(ii) Compressibility Compressibility is the property due to which a substance can be compressed, i.e., its volume can be decreased. Gases are compressible whereas solids and liquids are not.

(iii) Fluidity The property due to which a substance tends to flow is called fluidity. Gases and liquids are fluids, solids are not.

(iv) Filling a gas container A gas can be filled in a gas container by compressing it under high pressure. The property of compressibility (of gases) helps them in this regard.

(v) Shape The property of having a definite geometry is called shape of a particular substance. Solids have a definite shape whereas gases and liquids do not have.

(vi) Kinetic energy The energy possessed by an object or by the molecules of an object due to its state of motion is called kinetic energy. Molecules of gases posses highest kinetic energy. Increasing the temperature also increases the kinetic energy of a substance (or its molecules).

(vii) Density The mass per unit volume of a substance is called density.

Q3. Give reasons

(a) A gas fills completely the vessel in which it is kept.

Answer: There is little attraction between particles of gas. Thus, gas particles movefreely in all directions. Therefore, gas completely fills the vessel in which it is kept.

(b) A gas exerts pressure on the walls of the container.

Answer: Particles of gas move randomly in all directions at high speed. As a result, theparticles hit each other and also hit the walls of the container with a force. Therefore, gas exerts pressure on the walls of the container.

(c) A wooden table should be called a solid.

Answer: A wooden table has a definite shape and volume. It is very rigid and cannot be compressed i.e., it has the characteristics of a solid. Hence, a wooden table should be called a solid.

(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.

Answer: Particles of air have large spaces between them. On the other hand, wood has little space between its particles. Also, it is rigid. For this reason, we can easily move our hands in air, but to do the same through a solid block of wood, we need a karate expert.

Q4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Answer: The mass per unit volume of a substance is called density (density = mass/volume).As the volume of a substance increases, its density decreases. Though ice is a solid, it has large number of empty spaces between its particles. These spaces are larger as compared to the spaces present between the particles of water. Thus, the volume of ice is greater than that of water. Hence, the density of ice is less than that of water. A substance with lower density than water can float on water. Therefore, ice floats on water.

PROCESS OF CHANGE OF STATES OF MATTER:

• Vaporization

• Condensation

• Freezing

• Melting

• Sublimation

• Evaporation

VAPORIZATION:(CHANGE OF LIQUID INTO GAS):

The process of change of water into vapor is called vaporization. When water is heated after reaching at 1000C water starts boiling. At this temperature water turns into vapour. Since, water boils at 1000C, hence 1000C is called the boiling point of water.

BOILING POINTS

The common definition of boiling point is, the temperature at which a liquid boils is called its boiling point. Different liquid boils at different temperatures.

CONDENSATION:(CHANGE OF GAS INTO LIQUID)-

The change of vapor into water because of decrease in temperature is called condensation. Condensation is the reverse process of vaporization. When the temperature of vapor decreases it changes into water, this process is known as condensation.
Distilled water is manufactured by the condensation of vapor. The process of making of distilled water is known as distillation. In distillation first water is boiled to vaporize and the vapor is cooled, i.e. condensed to get distilled water.

FREEZING:(CHANGE OF LIQUID INTO SOLID) -

The change of liquid into solid because of decrease in temperature is called freezing. Water change into ice because of decrease in temperature, in other words water freezes into ice because of decrease in temperature. Water freezes at 00C.

MELTING:(CHANGE OF SOLID INTO LIQUID)

The change of solid into liquid due to increase in temperature is known as melting. Ice, which is a solid melts, i.e. changes into water at 00C.

LATENT HEAT

When water is heated up-to 1000C it starts boiling and changes into vapor. But we see thateven after continuous supply of heat temperature does not rise above the 100C while boiling of water. Temperature supplied after 100C to boiling water is used to change the water into vapor and temperature of water does not rise.On the other hand we see that when heat is supplied to ice, temperature does not rise above the 00C, until all ice melts. In this process also the heat supplied to ice after 00C is used to change of ice into water and temperature of ice does not rise.

♦ Heat is used in these processes without rise in temperature is known as Latent Heat. The latent heat is used in change of states of matter, such as from solid to liquid or from liquid to gas without rising in temperature.

♦ Hence, Latent heat is the heat released or absorbed by a body during the process without change in temperature of the system. This happens while change of state of matter meaning
a phase transition. Example - Melting of ice, boiling of water. The particles of solid and liquid are bonded together with great force of attraction, because of which a matter exists in a particular state. When we supply heat to a solid or liquid, the heat is supplied without come in notice is used to break the force of attraction between particles and this heat is not used to increase the kinetic energy of particles. Since, kinetic energy of particles do not increase we do not see any rise in temperature of the system. The word ‘latent’ is derived from the Latin word ‘Latere” which means “to lie hidden”. Joseph Black introduced the term Latent heat around 1762.

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