CHAPTER 1 Matter in our surroundings

Matters in our surroundings ( ch-1 ) notes

what is matter: Matter is anything that has mass and occupies space.
Example: Air, water, stone, etc.

🧭 Characteristics of Particles of Matter

Particles of matter are very small.
They have spaces between them.
They are constantly moving.
They attract each other.

🌡️ States of Matter

Solid
- Definite shape and volume
- Tightly packed particles
- Very strong force of attraction
- Cannot be compressed
Liquid
- No fixed shape but fixed volume
- Particles are less tightly packed
- Can flow
- Moderate attraction between particles
Gas
- Neither fixed shape nor volume
- Particles are far apart
- Can be highly compressed
- Weak force of attraction

📝 Note: Gases have the highest kinetic energy.

🔥 Change in State of Matter

Matter can change state by changing temperature or pressure.

1. Effect of Temperature:

On heating, particles gain energy → move faster → break bonds → change state.
Melting: Solid → Liquid
(Heat added at melting point)
Boiling: Liquid → Gas
(Heat added at boiling point)

2. Effect of Pressure:

Increase pressure → Gas changes to Liquid
Example: LPG cylinder (liquefied under pressure)

📊 Important Terms

Term	Definition
Latent Heat	Heat energy required to change the state of a substance without changing its temperature.
Latent Heat of Fusion	Heat required to convert 1 kg of solid into liquid without temperature change.
Latent Heat of Vaporisation	Heat required to convert 1 kg of liquid into gas without temperature change.

💨 Evaporation

Definition:
The process by which liquid changes into vapour at any temperature below boiling point.

🔑 Factors Affecting Evaporation:

Surface area – ↑ area → ↑ evaporation
Temperature – ↑ temp → ↑ evaporation
Humidity – ↑ humidity → ↓ evaporation
Wind speed – ↑ speed → ↑ evaporation

❄️ Cooling by Evaporation

When a liquid evaporates, it absorbs heat from surroundings, causing cooling.
🧾 Example: Sweat evaporates → body feels cool.

MCQ

🧠 Section A: Multiple Choice Questions (MCQs)

1. Which of the following is considered matter?
A. Heat
B. Air
C. Light
D. Sound

2. The process of particles moving from high to low concentration is:
A. Evaporation
B. Condensation
C. Diffusion
D. Melting

3. Which of these has the highest kinetic energy?
A. Ice
B. Water
C. Steam
D. Salt

4. The change of state from liquid to gas is known as:
A. Condensation
B. Freezing
C. Vaporisation
D. Melting

5. Which one is not a factor affecting evaporation?
A. Surface area
B. Wind speed
C. Shape of container
D. Humidity

6. Sublimation is shown by:
A. Camphor
B. Water
C. Ice
D. Salt

7. What is the boiling point of water in Kelvin?
A. 273 K
B. 300 K
C. 373 K
D. 350 K

8. Which state of matter is highly compressible?
A. Solid
B. Liquid
C. Gas
D. None

9. Matter is made up of:
A. Energy
B. Light
C. Particles
D. Waves

10. Which of the following is not a characteristic of particles of matter?
A. They have space between them
B. They are not moving
C. They attract each other
D. They are very small

11. The smell of perfume spreads due to:
A. Evaporation
B. Diffusion
C. Sublimation
D. Condensation

12. Conversion of gas into liquid is:
A. Sublimation
B. Condensation
C. Fusion
D. Evaporation

13. Which state of matter has a fixed volume but no fixed shape?
A. Solid
B. Liquid
C. Gas
D. Plasma

14. Which one of the following does not have a fixed shape?
A. Stone
B. Ice
C. Water
D. Iron

15. The process of melting involves:
A. Cooling
B. Condensation
C. Heating
D. Freezing

🔍 Section B: Assertion & Reason Questions

Choose the correct option:
(A) Both A and R are true, and R is the correct explanation of A.
(B) Both A and R are true, but R is not the correct explanation of A.
(C) A is true, but R is false.
(D) A is false, but R is true.

16.
Assertion (A): Air is a matter.
Reason (R): Air has mass and occupies space.

17.
Assertion (A): Ice floats on water.
Reason (R): Ice is denser than water.

18.
Assertion (A): Gases have high compressibility.
Reason (R): Gas particles have large spaces between them.

19.
Assertion (A): Solids have definite shape and volume.
Reason (R): The particles in solids are tightly packed.

20.
Assertion (A): Liquids cannot be compressed easily.
Reason (R): Particles in liquids have large spaces between them.

21.
Assertion (A): Evaporation causes cooling.
Reason (R): During evaporation, particles absorb heat from surroundings.

22.
Assertion (A): Liquids take the shape of the container.
Reason (R): Liquid particles are not rigidly fixed.

23.
Assertion (A): Camphor shows sublimation.
Reason (R): Sublimation is a process where solid directly turns into gas.

24.
Assertion (A): Temperature increases during change of state.
Reason (R): Latent heat is used to increase temperature.

25.
Assertion (A): The boiling point of water is 373 K.
Reason (R): Water boils at 100°C, which is equal to 373 K.

26.
Assertion (A): Water vapour condenses into water on cooling.
Reason (R): Cooling increases kinetic energy of particles.

27.
Assertion (A): Matter is made up of tiny particles.
Reason (R): The spaces between particles are zero.

28.
Assertion (A): Gases do not have a fixed shape or volume.
Reason (R): The particles in gases move freely in all directions.

29.
Assertion (A): Naphthalene balls reduce in size over time.
Reason (R): They undergo sublimation.

30.
Assertion (A): Melting of ice is an exothermic process.
Reason (R): Heat is absorbed during melting.

📘 Section C: Case-Based Questions

Case Study 1:
Riya places a bowl of water near a sunny window and another bowl in a shaded area. She observes that the water near the window evaporates faster. She also notices that on a hot day, her wet clothes dry quickly when there’s strong wind.

31. Which process is being observed?
A. Boiling
B. Melting
C. Evaporation
D. Condensation

32. What factor helped water evaporate faster near the window?
A. Lower temperature
B. Higher humidity
C. Higher temperature
D. Closed space

33. Which factor affects drying of clothes in wind?
A. Surface area
B. Wind speed
C. Shape of cloth
D. Pressure

34. Why is water evaporating faster in sunlight?
A. Decreased pressure
B. Increased kinetic energy of particles
C. Formation of ice
D. Less air movement

35. What change is happening in the state of matter during evaporation?
A. Solid to gas
B. Liquid to gas
C. Gas to liquid
D. Liquid to solid

✅ Answer Key

MCQs:

Assertion & Reason:

Case-Based:

Reason – based question/answer

Q1. Why do we feel cool after sweating?

Answer: Because sweat takes heat from our skin to evaporate. This cools our body.

Q2. Why are gases easy to compress?

Answer: Because gas particles are far apart. So they can be pressed closer easily.

Q3. Why does ice float on water?

Answer: Because ice is lighter than water. It has more empty space between its particles.

Q4. Why does hot food smell from far away?

Answer: Because heat makes gas particles move faster. So the smell spreads quickly in the air.

Q5. Why do clothes dry faster on a windy day?

Answer: Because wind blows away the water vapour. This helps water to evaporate faster.

Q6. Why do naphthalene balls disappear over time?

Answer: Because they change directly from solid to gas. This is called sublimation.

Q7. Why are solids hard and not easy to press?

Answer: Because their particles are tightly packed. They cannot move or be compressed easily.

Q8. Why do liquids have a fixed volume but no fixed shape?

Answer: Because their particles are close together but can move around. So they flow and take the shape of the container.

Q9. Why does water evaporate faster when heated?

Answer: Because heat gives more energy to the particles. They move faster and escape as vapour.

Q10. Why is LPG stored in cylinders under pressure?

Answer: Because high pressure turns the gas into liquid. It makes it easy to store and transport.

Q11. Why does camphor disappear in open air?

Answer: Because it directly changes from solid to gas. This process is sublimation.

Q12. Why is latent heat called hidden heat?

Answer: Because it changes the state of a substance without changing its temperature.

Q13. Why does water appear on the outside of a cold glass?

Answer: Because water vapour in the air cools and turns into liquid water. This is called condensation.

Q14. Why does gas turn into liquid when pressure is increased?

Answer: Because particles come closer together. This turns gas into liquid.

Q15. Why does perfume spread all over the room quickly?

Answer: Because gas particles move freely in all directions. This is called diffusion.