Matter in Our Surroundings

Matter is everything that occupies space and has mass. Everything around us, including air, water, food, and even the chair you sit on, is made up of matter. In this chapter, we explore the physical nature of matter, its states, and the changes it undergoes due to various conditions. By understanding matter, we gain insights into the nature of substances that make up the world.

1. Physical Nature of Matter

– Matter is Made of Particles:

Matter is not continuous but made up of small particles. These particles are too small to be seen even with a microscope.

Experiments like dissolving sugar in water prove the presence of these particles, as sugar particles disappear in water and uniformly mix without increasing the volume.

– Characteristics of Particles of Matter:

 a) Particles of matter have space between them: When sugar is dissolved in water, the particles of sugar fit into the spaces between the water particles.

b) Particles of matter are continuously moving: The particles of matter are in constant motion and this motion increases with temperature.

c) Particles of matter attract each other: There is a force of attraction between particles of matter, which keeps them together. This force varies between different types of matter.

2. States of Matter

Matter can exist in three different states: solid, liquid, and gas. These states are determined by the arrangement and movement of particles.

– 1. Solids:

Solids have a definite shape and volume.

The particles in solids are closely packed, resulting in strong forces of attraction between them.

The movement of particles in solids is minimal, limited to vibrations about their fixed positions.

Solids are rigid and cannot be compressed easily.

Examples: Iron, ice, wood.

– 2. Liquids:

Liquids have a definite volume but no fixed shape. They take the shape of the container they are in.

Particles in liquids are less tightly packed than in solids, allowing them to move more freely.

The forces of attraction between particles in liquids are weaker than in solids but stronger than in gases.

Liquids can flow and are not easily compressible.

Examples: Water, milk, oil.

– 3. Gases:

Gases have neither a definite shape nor a definite volume. They fill the container they are in.

Particles in gases are far apart and move freely in all directions.

The forces of attraction between particles are negligible.

Gases are highly compressible and can flow easily.

Examples: Air, oxygen, carbon dioxide.

3. Can Matter Change Its State?

Matter can change from one state to another when the temperature or pressure changes. These changes are due to the energy provided to the particles, which alters their movement and arrangement.

– 1. Effect of Temperature:

Melting (Solid to Liquid): When a solid is heated, its particles gain energy, vibrate more vigorously, and break free from their fixed positions, turning into a liquid. The temperature at which a solid turns into a liquid is called the melting point. The melting point of ice is 0°C.

Boiling (Liquid to Gas): When a liquid is heated, its particles gain enough energy to overcome the forces of attraction between them and escape into the air as gas. The temperature at which a liquid turns into gas is called the boiling point. The boiling point of water is 100°C.

Condensation (Gas to Liquid): Cooling a gas decreases the energy of the particles, causing them to slow down and come closer, turning the gas into a liquid.

Freezing (Liquid to Solid): When a liquid is cooled, the movement of its particles decreases, and they come together to form a solid.

– 2. Effect of Pressure:

By increasing pressure, gases can be compressed into liquids. This principle is used in the liquefaction of gases.

Decreasing the pressure allows a liquid to evaporate more easily.

4. Sublimation:

Sublimation is the process by which a solid directly changes into a gas without passing through the liquid state. The reverse process is called deposition.

Examples of Sublimation: Camphor, iodine, and dry ice (solid carbon dioxide).

5. Evaporation: A Cooling Process

Evaporation is the process by which a liquid changes into vapor at a temperature below its boiling point. It occurs at the surface of the liquid and can take place at any temperature.

– 1. Factors Affecting Evaporation:

Temperature: Higher temperatures increase the rate of evaporation as particles gain more energy.

Surface Area: The larger the surface area, the faster the rate of evaporation.

Humidity: Evaporation decreases in high humidity because the air already contains a significant amount of water vapour.

Wind Speed: Increased wind speed removes water vapour from the air, increasing the rate of evaporation.

– 2. Evaporation Causes Cooling:

During evaporation, the particles with higher energy escape from the surface of the liquid, leaving behind the particles with lower energy. This lowers the temperature of the remaining liquid, causing cooling.

Examples: Sweating helps cool our body as sweat evaporates, and earthen pots keep water cool because water evaporates from their porous surface.

6. Latent Heat:

Latent heat is the heat energy required to change the state of a substance without changing its temperature.

– 1. Latent Heat of Fusion: 

The amount of heat energy required to change 1 kg of a solid into a liquid at its melting point without a change in temperature. For ice, it is 334 kJ/kg. 

– 2. Latent Heat of Vaporization: 

The amount of heat energy required to change 1 kg of a liquid into gas at its boiling point without a change in temperature. For water, it is 2260 kJ/kg.

7. Interconversion of States of Matter:

Matter can change from one state to another based on temperature and pressure conditions. The process is reversible.

 Solid ↔ Liquid ↔ Gas

   – Solid to Liquid (Melting) and Liquid to Solid (Freezing).

   – Liquid to Gas (Boiling) and Gas to Liquid (Condensation).

   – Solid to Gas (Sublimation) and Gas to Solid (Deposition).

These changes occur due to the exchange of heat energy, which affects the kinetic energy of the particles.

°Hi Shortly:

Matter can exist in different states based on the arrangement and energy of its particles. These states are interconvertible by changing the temperature and pressure. The understanding of matter and its behavior under different conditions helps us to explain various natural phenomena and also forms the foundation for studying more complex concepts in chemistry.

– Summary:

Matter is made of particles that have space between them, are in continuous motion, and attract each other.

Matter exists in three states: solid, liquid, and gas.

Chances in temperature and pressure can cause matter to change its state.

Sublimation is the direct change of a solid into a gas.

Evaporation is a cooling process and is affected by temperature, surface area, humidity, and wind speed.

Latent heat is the energy required to change the state of matter without changing its temperature.

This foundational understanding of matter is essential for exploring more advanced concepts in physics and chemistry.

Exercise Questions: Chapter 1 – Matter: In Our Surroundings

(Based on NCERT Class 9 Science)

Section 1: Physical Nature of Matter

1. What is matter ? 

   a) Anything that has mass and occupies space  

   b) Anything that does not occupy space  

   c) Only gases  

   d) Only solids and liquids  

2. Explain how dissolving sugar in water proves that matter is made up of particles.

3. State three characteristics of particles of matter with examples.

4. Fill in the blanks: 

   a) Matter is made up of _________.  

   b) Particles of matter are _________ moving.  

   c) Particles of matter have _________ between them.  

Section 2: States of Matter

1. Define the three states of matter and give two examples for each.

2. Which of the following statements are true for solids? 

   a) Solids have a definite shape and volume.  

   b) Solids are compressible.  

   c) The particles of a solid are closely packed.  

   d) Solids can flow.

3. Differentiate between the characteristics of solids, liquids, and gases in terms of shape, volume, compressibility, and particle arrangement.

4. Match the following:

Column A (States)

Column B (Properties) 

a) Solids

i) Have neither a fixed shape nor a fixed volume

b) Liquids

ii) Have a definite shape and volume

c) Gases

iii) Have a definite volume but no definite shape

 Section 3: Can Matter Change Its State?

1. Explain how the states of matter change due to:

   a) An increase in temperature  

   b) A decrease in temperature

2. What is the melting point? At what temperature does ice melt?

3. How does the effect of pressure change the state of matter? Give an example.

4. Fill in the blanks:

   a) The temperature at which a liquid changes into a gas is called its _________.  

   b) The process of gas changing into a liquid is called _________.  

   c) The temperature at which a solid changes into a liquid is called its _________.  

Section 4: Sublimation

1. What is sublimation? Give two examples of substances that undergo sublimation.

2. Differentiate between sublimation and deposition.

3. Why does dry ice (solid CO₂) sublimate at room temperature?

Section 5: Evaporation: A Cooling Process

1. What is evaporation and how does it differ from boiling?

2. Explain why sweating causes cooling in our bodies.

3. Describe the factors that affect the rate of evaporation.

4. State whether the following statements are True or False:

   a) Higher the humidity, faster the evaporation.  

   b) Evaporation causes cooling.  

   c) Evaporation only occurs at high temperatures.  

Section 6: Latent Heat

1. Define latent heat of fusion and latent heat of vaporisation.

2. Why does the temperature remain constant during the melting of ice even though heat is being supplied?

3. Calculate the amount of heat required to convert 1 kg of ice into water at 0°C. (Latent heat of fusion of ice is 334 kJ/kg).

Section 7: Interconversion of States of Matter

1. Describe the processes involved in the interconversion of states of matter with diagrams.

2. Explain the relationship between temperature, pressure, and the state of matter.

3. What are the conditions under which:

   a) Solid converts into liquid?  

   b) Liquid converts into gas?  

   c) Gas converts into liquid?

4. Draw a flowchart to show the interconversion of states of matter.

Higher Order Thinking Skills (HOTS) Questions:

1. Why are gases compressible but solids are not?

2. If a substance has a fixed volume but no fixed shape, what can you conclude about its state? Explain.

3. Why does evaporation of water in an earthen pot cool the water inside?

These exercises cover the fundamental concepts discussed in the chapter, providing studen

ts with the opportunity to test their understanding of the physical nature and states of matter, as well as the factors that influence changes in matter’s state