# NCERT Class 9 Science Chapter 1 ‘Matter in Our Surroundings’ Notes (Free PDF)

We have prepared well-written NCERT Class 9 Science Chapter 1 ”Matter in Our Surroundings’ Notes for you. These notes are written in such a manner as to facilitate easy memorising of chapters and will serve as a method of quick revision to help you ace your exams. Let us explore them now!

## Introduction to NCERT Class 9 Science Chapter 1 Matter in Our Surroundings Notes

In NCERT Class 9 Science Chapter 1, we will learn about the nature of matter, solids, liquids, gases, their related properties, etc. Starting with the characteristics of particles, we will then study about individual states of matter in detail. After that, we will cover the effects of temperature and pressure on matter and lastly, we will understand and learn about evaporation Let us begin.

## Physical Nature of Matter

Matter is made up of particles and these particles are very small. For example, one crystal of Potassium permanganate when dissolved in water, keeps on dividing into smaller and smaller particles.

### Characteristics of Particles of Matter

Some of the characteristics of particles of matter are mentioned below:

• Particles of matter have space between them: 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.
• Particles of matter attract each other: Particles of matter have a 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.

## States of Matter

Matter mainly exists in three states: Solid, Liquid and Gaseous. Let us look at their respective properties in detail.

### The Solid State

• Solids have a definite shape.
• They have distinct boundaries and fixed volumes.
• Solids 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.

### The Liquid State

• Liquids have no fixed shape but have a fixed volume.
• Liquids take up the shape of the container in which they are kept.
• Liquids flow and change shape, so they are not rigid but can be called fluid.
• Solids, liquids and gases can diffuse into liquids.
• The rate of diffusion of liquids is much more than solids because they are much more free to move and have greater spaces in between particles.

### The Gaseous State

• Gases are highly compressible as compared to solids and liquids. The liquefied petroleum gas (LPG) cylinder that we get in our homes for cooking or the oxygen supplied to hospitals in cylinders is compressed gas.
• Compressed natural gas (CNG) is used as fuel these days in vehicles. Due to its high compressibility, large volumes of gas can be compressed into a small cylinder and transported easily.
• Due to the high speed of particles and the large space between them, gases show the property of diffusing very fast into other gases.
• 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.

## Can Matter Change its State?

The state of matter can be changed into another state by changing the temperature and pressure. Let us look at how these changes happen.

### In Solids

• Solids on reaching a particular temperature change their state to liquid. The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called melting point
• The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely.
• The melting point of a solid is an indication of the strength of the force of attraction between its particles.
• The melting point of ice is 273.15 K.
• The process of melting, that is, the change of a solid state into a liquid state is also known as fusion
• During melting, the temperature of the solid remains the same.
• 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
• Particles in water at 0 Degrees C (273 K) have more energy as compared to particles in ice at the same temperature.

### In Liquids

• On heating, liquids change their state into gas.
• 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.
• For water, this temperature is 373 K (100C = 273 + 100 = 373 K).
• Particles in steam, that is, water vapour at 373 K (100 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.

A change of state directly from solid to gas without changing into liquid state is called sublimation and the direct change of gas to solid without changing into liquid is called deposition

### Effect of Change of Pressure

• Applying pressure and reducing temperature can liquefy gases.
• Solid CO2 is stored under high pressure. Solid CO2 gets converted directly into the gaseous state on the decrease of pressure to 1 atmosphere without changing into the liquid state. This is the reason that solid carbon dioxide is also known as dry ice.

## Evaporation

The phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation

In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and get converted into vapour.

### Factors affecting Evaporation

The rate of evaporation increases with:

• An increase in surface area: We know that evaporation is a surface phenomenon. If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out.
• An increase in temperature: With the increase in temperature, more number of particles get enough kinetic energy to go into the vapour state.
• A decrease in humidity: Humidity is the amount of water vapour present in the air. The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in the air is already high, the rate of evaporation decreases.
• An increase in wind speed: It is a common observation that 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 surroundings.

### How does Evaporation Cause Cooling?

The particles of liquid absorb energy from the surroundings to regain the energy lost during evaporation. This absorption of energy from the surroundings makes the surroundings cold.

During summer, we perspire more because of the mechanism of our body which keeps us cool.

The heat energy equal to the latent heat of vaporisation is absorbed from the body leaving the body cool.

## Important Definitions in NCERT Class 9 Science Chapter 1 Matter in Our Surroundings Notes

Some important definitions covered in the  NCERT Class 9 Geography Chapter 1 notes are mentioned below:

• Melting point: Solids on reaching a particular temperature change their state to liquid. The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called melting point.
• Fusion: The process of melting, that is, the change of a solid state into a liquid state is also known as fusion.
• Latent heat of fusion: 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.
• Boiling Point: The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.
• Sublimation: A change of state directly from solid to gas without changing into liquid state is called sublimation.
• Deposition: The direct change of gas to solid without changing into liquid is called deposition.
• Evaporation: The phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.

## FAQs

Q1. What is matter class 9 science chapter 1?

Ans: Matter is made up of particles and these particles are very small. For example, one crystal of Potassium permanganate when dissolved in water, keeps on dividing into smaller and smaller particles.

Q2. What is dry ice Class 9?

Ans: Dry ice is Solid CO2. Solid CO2 is stored under high pressure. Solid CO2 gets converted directly into the gaseous state on the decrease of pressure to 1 atmosphere without changing into the liquid state. This is the reason that solid carbon dioxide is also known as dry ice.

Q3. Which gas is called dry ice?

Ans: Solid CO2 is called dry ice.

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