Online Self Test
Learn & Practice Quizzes & Challenges Competitive Exams
 

Matter in Our Surroundings – CBSE NCERT Study Resources

Next Chapter
Previous Chapter Next Chapter

Study Materials

9th

9th - Science

Matter in Our Surroundings

Jump to Question Sets

Overview of the Chapter

This chapter introduces students to the concept of matter, its various states, and the characteristics that define them. It explores how matter changes from one state to another under different conditions and explains the behavior of particles in each state.

Matter: Anything that occupies space and has mass is called matter. It is made up of tiny particles.

States of Matter

Matter exists in three primary states: solid, liquid, and gas. Each state has distinct properties based on the arrangement and movement of particles.

Solids

Solids have a definite shape and volume. The particles are tightly packed and vibrate in fixed positions.

Liquids

Liquids have a definite volume but no fixed shape. The particles are loosely packed and can move around each other.

Gases

Gases have neither a definite shape nor volume. The particles are far apart and move freely in all directions.

Diffusion: The process by which particles of matter intermix on their own due to their kinetic energy.

Change of State

Matter can change from one state to another by altering temperature or pressure. Common processes include melting, evaporation, condensation, and sublimation.

Melting

The process by which a solid changes into a liquid upon heating.

Evaporation

The process by which a liquid changes into a gas at temperatures below its boiling point.

Condensation

The process by which a gas changes into a liquid upon cooling.

Sublimation

The process by which a solid directly changes into a gas without passing through the liquid state.

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

Factors Affecting Evaporation

Evaporation is influenced by factors such as temperature, surface area, humidity, and wind speed.

Summary

This chapter helps students understand the fundamental properties of matter and the processes involved in changing its states. It lays the foundation for further studies in chemistry and physics.

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
What is the boiling point of water at sea level?
Answer:

100°C

Question 2:
Name the process by which a solid changes directly into a gas.
Answer:

Sublimation

Question 3:
Give an example of sublimation from NCERT.
Answer:

Dry ice (solid CO2)

Question 4:
What is the SI unit of temperature?
Answer:

Kelvin (K)

Question 5:
Which state of matter has the highest compressibility?
Answer:

Gases

Question 6:
What is the melting point of ice?
Answer:

0°C

Question 7:
Name the process by which water vapor changes into liquid water.
Answer:

Condensation

Question 8:
Give a real-world example of evaporation.
Answer:

Drying of clothes

Question 9:
What is the physical state of matter with definite volume but no definite shape?
Answer:

Liquid

Question 10:
Name the property due to which gases fill their container completely.
Answer:

Diffusion

Question 11:
What is the effect of temperature on the rate of evaporation?
Answer:

Increases with temperature

Question 12:
Give an NCERT example of diffusion in gases.
Answer:

Smell of perfume spreading

Question 13:
Define matter.
Answer:

Matter is anything that occupies space and has mass. It includes everything around us, such as air, water, and solids.

Question 14:
What are the three states of matter?
Answer:

The three states of matter are:
Solid (fixed shape and volume),
Liquid (fixed volume but no fixed shape),
Gas (no fixed shape or volume).

Question 15:
Why do gases exert pressure on the walls of their container?
Answer:

Gases exert pressure because their particles move randomly and collide with the container walls, creating force per unit area.

Question 16:
What is sublimation? Give an example.
Answer:

Sublimation is the process where a solid changes directly into gas without becoming a liquid. Example: Dry ice (solid CO₂) sublimes at room temperature.

Question 17:
Why does a sponge compress though it is a solid?
Answer:

A sponge has tiny pores filled with air. When pressed, the air escapes, making it compressible, but it regains shape due to its solid structure.

Question 18:
What is the boiling point of water at standard pressure?
Answer:

The boiling point of water at standard pressure (1 atm) is 100°C (373 K).

Question 19:
Why do we feel cool when we apply acetone or perfume on our skin?
Answer:

Acetone/perfume absorbs latent heat of vaporization from the skin to change into vapour, causing a cooling sensation.

Question 20:
Name the process by which a gas changes directly into a solid.
Answer:

The process is called deposition. Example: Formation of frost from water vapour.

Question 21:
Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer:

Ice absorbs additional latent heat from the surroundings to melt into water, providing more cooling effect than water at 273 K.

Question 22:
What is the SI unit of temperature?
Answer:

The SI unit of temperature is Kelvin (K).

Question 23:
Why do gases diffuse faster than liquids?
Answer:

Gases have higher kinetic energy and larger interparticle spaces, allowing faster movement and diffusion compared to liquids.

Question 24:
Define evaporation. How does it differ from boiling?
Answer:

Evaporation is the surface phenomenon where liquid changes to vapour at any temperature, while boiling occurs at a fixed temperature throughout the liquid.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
Define matter and give two examples.
Answer:

Matter is anything that occupies space and has mass.
Examples: Water, Air.

Question 2:
What is the boiling point of water at standard atmospheric pressure?
Answer:

The boiling point of water at standard atmospheric pressure is 100°C (373 K).

Question 3:
Name the process by which a solid directly changes into a gas.
Answer:

The process is called sublimation. Example: Dry ice (solid CO2) sublimates into gas.

Question 4:
What happens to the kinetic energy of particles when a liquid is heated?
Answer:

The kinetic energy of particles increases, causing them to move faster and eventually change into the gaseous state.

Question 5:
Why does a sponge, though solid, compress on pressing?
Answer:

A sponge has tiny pores filled with air. On pressing, the air escapes, making it compressible like a porous solid.

Question 6:
Differentiate between evaporation and boiling.
Answer:
  • Evaporation: Occurs at any temperature, only at the surface.
  • Boiling: Occurs at fixed temperature, throughout the liquid.
Question 7:
Why do we feel cool after sweating?
Answer:

Sweat evaporates, absorbing latent heat from our body, causing a cooling effect.

Question 8:
What is the SI unit of temperature? Convert 25°C to Kelvin.
Answer:

SI unit: Kelvin (K).
Conversion:
K = °C + 273
25°C = 25 + 273 = 298 K.

Question 9:
Why does the smell of perfume spread quickly in a room?
Answer:

Perfume particles diffuse due to high kinetic energy in gases, spreading rapidly in all directions.

Question 10:
What is the physical state of water at: (a) 25°C (b) 0°C?
Answer:

(a) Liquid (below boiling point)
(b) Solid/Liquid (melting/freezing point, depends on heat exchange).

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Define matter and list its three basic states with examples.
Answer:

Matter is anything that occupies space and has mass. The three basic states of matter are:

  • Solid: Definite shape and volume (e.g., iron, wood)
  • Liquid: Definite volume but no fixed shape (e.g., water, oil)
  • Gas: No fixed shape or volume (e.g., oxygen, carbon dioxide)

These states arise due to differences in the arrangement and energy of particles.

Question 2:
Explain why solids have a fixed shape but liquids and gases do not.
Answer:

Solids have a fixed shape because their particles are tightly packed in a rigid structure with strong intermolecular forces, restricting movement.
Liquids and gases lack a fixed shape because:
1. Liquids: Particles are loosely packed with moderate forces, allowing flow.
2. Gases: Particles are far apart with negligible forces, moving freely to fill containers.

Question 3:
Describe the process of sublimation with an example.
Answer:

Sublimation is the direct transition of a substance from solid to gas without passing through the liquid phase.
Example: Dry ice (solid CO2) sublimes at room temperature, forming CO2 gas.
This occurs because the particles gain enough energy to overcome intermolecular forces directly.

Question 4:
How does temperature affect the state of matter? Illustrate with water.
Answer:

Temperature changes the kinetic energy of particles, altering their state:
1. 0°C: Water freezes into ice (solid).
2. 0°C to 100°C: Water remains liquid.
3. 100°C: Water boils into vapor (gas).
Higher temperatures weaken intermolecular forces, enabling phase transitions.

Question 5:
Explain why solids have a fixed shape but gases do not.
Answer:

Solids have a fixed shape because their particles are tightly packed in a rigid structure with strong intermolecular forces, restricting movement.
Gases lack a fixed shape because their particles are far apart with weak forces, allowing them to move freely and fill any container.

Question 6:
How does temperature affect the rate of evaporation?
Answer:

Higher temperature increases the rate of evaporation because:

  • Particles gain more kinetic energy.
  • More molecules escape the liquid surface.

Example: Clothes dry faster in summer due to increased heat.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the interconversion of states of matter with examples. How does temperature affect this process?
Answer:
Concept Overview

Matter changes states (solid, liquid, gas) due to energy changes. Our textbook shows melting, freezing, and evaporation as examples.


Process Explanation
  • Heating ice (solid) turns it to water (liquid).
  • Cooling water vapor (gas) forms dew (liquid).

Real-world Application

In summers, water evaporates faster, showing temperature's role. NCERT mentions dry ice subliming at room temperature.

Question 2:
Describe diffusion with an experiment. Why does it occur faster in gases than liquids?
Answer:
Concept Overview

Diffusion is mixing particles due to motion. We studied it using potassium permanganate in water.


Process Explanation
  • Drop ink in water: spreads slowly (liquid).
  • Perfume smell spreads fast (gas).

Real-world Application

Gases diffuse faster due to more space between particles. NCERT shows honey mixing slower than oxygen in air.

Question 3:
What is latent heat? Explain its role in melting ice. Give a daily-life example.
Answer:
Concept Overview

Latent heat is energy absorbed/released during state change without temperature change.


Process Explanation
  • Ice at 0°C needs heat to melt but stays at 0°C.
  • This energy breaks ice’s rigid structure.

Real-world Application

Coolers use water evaporation (absorbing heat) to cool air. NCERT mentions steam causing severe burns due to latent heat.

Question 4:
Compare evaporation and boiling. How does surface area affect evaporation?
Answer:
Concept Overview

Both convert liquid to gas, but boiling needs bulk heating, while evaporation occurs at all temperatures.


Process Explanation
  • Boiling: Bubbles form (100°C for water).
  • Evaporation: Slow (e.g., drying clothes).

Real-world Application

Wet floors dry faster when spread out (more surface area). NCERT shows ponds drying slower than shallow pans.

Question 5:
Why do gases exert pressure? Describe an activity to show gas pressure.
Answer:
Concept Overview

Gas particles collide with container walls, creating pressure. We studied it using a syringe.


Process Explanation
  • Sealed syringe: Particles hit walls when compressed.
  • Balloon inflates due to air pressure.

Real-world Application

CNCERT shows LPG cylinders storing gas under high pressure. Bicycle tires burst if overfilled.

Question 6:
Explain the interconversion of states of matter with examples from daily life and NCERT.
Answer:
Concept Overview

Matter changes states due to temperature or pressure changes. We studied three states: solid, liquid, and gas.


Process Explanation
  • Melting: Ice (solid) to water (liquid).
  • Evaporation: Water (liquid) to vapor (gas).
  • Condensation: Vapor (gas) to dew (liquid).

Real-world Application

Our textbook shows dry ice subliming. In daily life, we see water boiling to steam while cooking.

Question 7:
Describe diffusion with an experiment and its importance.
Answer:
Concept Overview

Diffusion is the mixing of particles due to their motion. We studied it in gases and liquids.


Process Explanation
  • Experiment: Drop ink in water—particles spread slowly.
  • NCERT example: Smell of perfume spreads in air.

Real-world Application

Respiration uses oxygen diffusion in blood. Cooking smells spread due to diffusion.

Question 8:
How does temperature affect the state of matter? Give NCERT and practical examples.
Answer:
Concept Overview

Temperature changes kinetic energy, altering matter's state.


Process Explanation
  • NCERT: Wax melts on heating.
  • Water freezes below 0°C.

Real-world Application

We see ice cream melting in summer. Our textbook shows molten iron solidifying on cooling.

Question 9:
Explain latent heat with its types and daily-life applications.
Answer:
Concept Overview

Latent heat is energy absorbed/released during state change without temperature change.


Process Explanation
  • Fusion: Ice to water (absorbed).
  • Vaporization: Water to steam (absorbed).

Real-world Application

NCERT shows sweat cooling us. We use it in refrigerators for cooling.

Question 10:
What is sublimation? Give an experiment and its uses.
Answer:
Concept Overview

Sublimation is direct solid-to-gas change, skipping liquid state.


Process Explanation
  • Experiment: Iodine crystals heat to purple vapor.
  • NCERT example: Dry ice (CO₂) subliming.

Real-world Application

Used in air fresheners. Camphor sublimates in temples.

Question 11:
Explain the process of evaporation with examples from daily life. How does it differ from boiling? Support your answer with a labeled diagram showing the arrangement of particles during evaporation.
Answer:

Evaporation is the process by which a liquid changes into its vapour state at any temperature below its boiling point. It occurs only at the surface of the liquid. Examples from daily life:

  • Drying of clothes under the sun
  • Cooling effect when sweat evaporates from our skin
  • Formation of salt from seawater

Difference from boiling:

  • Evaporation occurs at all temperatures, while boiling occurs only at the boiling point.
  • Evaporation is a surface phenomenon, whereas boiling involves the entire liquid.
  • Evaporation is a slow process, while boiling is rapid.

Diagram: (Imagine a beaker of water with arrows showing water molecules escaping from the surface. The particles are loosely packed in the liquid state, and some are shown transitioning to the gaseous state above the liquid.)

Question 12:
Describe an activity to demonstrate that particles of matter are continuously moving. Explain the observations and conclusions with reference to the kinetic theory of matter.
Answer:

Activity: Take a beaker filled with water and carefully add a drop of ink or potassium permanganate solution. Observe the spreading of colour.

Observations:

  • The colour slowly spreads throughout the water.
  • Eventually, the entire solution becomes uniformly coloured.

Explanation (Kinetic Theory):

The particles of matter (here, ink and water) possess kinetic energy and are in continuous motion. The ink particles diffuse into the spaces between water particles, and vice versa, due to their random motion. This proves:

  • Matter is made up of tiny particles.
  • These particles are always moving (kinetic energy).
  • There are intermolecular spaces between particles.

Application: This principle explains phenomena like smell spreading in a room or tea brewing in hot water.

Question 13:
Explain the process of evaporation with suitable examples. How does it differ from boiling? Discuss the factors affecting the rate of evaporation.
Answer:

Evaporation is the process by which a liquid changes into its vapour state at any temperature below its boiling point. It occurs at the surface of the liquid. For example, wet clothes dry when hung outside due to evaporation of water. Similarly, sweating cools our body as sweat evaporates from the skin.


Difference between evaporation and boiling:

  • Evaporation occurs at all temperatures, while boiling occurs only at the boiling point.
  • Evaporation is a surface phenomenon, whereas boiling involves the entire liquid.
  • Evaporation is a slow process, while boiling is rapid.

Factors affecting the rate of evaporation:

  • Temperature: Higher temperature increases evaporation.
  • Surface area: Larger surface area speeds up evaporation.
  • Humidity: Lower humidity promotes faster evaporation.
  • Wind speed: Higher wind speed increases evaporation.
Question 14:
Describe the interconversion of states of matter with the help of a labelled diagram. Explain how temperature and pressure influence these changes.
Answer:

The interconversion of states of matter refers to the transformation of a substance from one state (solid, liquid, gas) to another due to changes in temperature or pressure. Below is a brief explanation with key processes:


Processes involved:

  • Melting: Solid to liquid (e.g., ice to water).
  • Freezing: Liquid to solid (e.g., water to ice).
  • Evaporation: Liquid to gas (e.g., water to vapour).
  • Condensation: Gas to liquid (e.g., vapour to water droplets).
  • Sublimation: Solid directly to gas (e.g., dry ice to CO₂ gas).
  • Deposition: Gas directly to solid (e.g., frost formation).

Role of temperature and pressure:

  • Temperature: Increasing temperature provides energy to break intermolecular forces, causing melting or evaporation. Decreasing temperature reverses these processes.
  • Pressure: High pressure can compress gases into liquids (e.g., LPG). Low pressure can cause liquids to evaporate faster.

For example, increasing the temperature of ice melts it into water, and further heating converts it to vapour. Applying pressure to a gas can liquefy it, as seen in CNG cylinders.


(Note: A labelled diagram would show arrows between solid, liquid, and gas states with process names like melting, freezing, etc.)

Question 15:
Describe the interconversion of states of matter with the help of a labeled diagram. Explain how temperature and pressure influence these changes.
Answer:

The interconversion of states of matter refers to the transformation of a substance from one state (solid, liquid, gas) to another due to changes in temperature or pressure. Below is a brief explanation along with key processes:


Processes involved:

  • Melting: Solid to liquid (e.g., ice to water).
  • Freezing: Liquid to solid (e.g., water to ice).
  • Evaporation: Liquid to gas (e.g., water to vapour).
  • Condensation: Gas to liquid (e.g., vapour to water droplets).
  • Sublimation: Solid directly to gas (e.g., dry ice).
  • Deposition: Gas directly to solid (e.g., frost formation).

Role of temperature and pressure:

  • Temperature: Increasing temperature provides energy to break intermolecular forces, causing melting or evaporation. Decreasing temperature reverses these changes.
  • Pressure: High pressure can compress gases into liquids (e.g., LPG). Low pressure can cause liquids to evaporate faster.

Here’s a simple labeled diagram for clarity:

[Diagram: A circular flowchart showing solid, liquid, and gas states with arrows labeled melting, freezing, evaporation, condensation, sublimation, and deposition.]


These concepts are vital in understanding natural processes like the water cycle and industrial applications like refrigeration.

Question 16:
Describe the interconversion of states of matter with the help of a labeled diagram. Explain how latent heat plays a role in these changes.
Answer:

The interconversion of states of matter refers to the transformation between solid, liquid, and gas states due to changes in temperature or pressure. Below is a brief explanation with key processes:


Processes:

  • Melting: Solid to liquid (e.g., ice to water).
  • Freezing: Liquid to solid (e.g., water to ice).
  • Evaporation/Boiling: Liquid to gas (e.g., water to steam).
  • Condensation: Gas to liquid (e.g., steam to water droplets).
  • Sublimation: Solid directly to gas (e.g., dry ice to CO₂ gas).
  • Deposition: Gas directly to solid (e.g., frost formation).

Role of Latent Heat:

Latent heat is the energy absorbed or released during a state change without temperature change. For example:

  • Latent heat of fusion: Energy needed to melt a solid (absorbed) or freeze a liquid (released).
  • Latent heat of vaporization: Energy needed to vaporize a liquid (absorbed) or condense a gas (released).

This energy breaks or forms intermolecular forces, enabling state changes. A labeled diagram would show these transitions with arrows indicating heat absorption/release.

Question 17:
Explain the process of evaporation with suitable examples. How does it differ from boiling? Discuss the factors affecting evaporation.
Answer:

Evaporation is the process by which a liquid changes into its vapour state at any temperature below its boiling point. Unlike boiling, evaporation occurs only at the surface of the liquid and does not involve the formation of bubbles. For example, wet clothes dry up when hung in the sun because water evaporates from their surface. Similarly, water in a pond slowly decreases over time due to evaporation.


Differences between Evaporation and Boiling:

  • Temperature: Evaporation occurs at all temperatures, while boiling occurs only at the boiling point of the liquid.
  • Location: Evaporation happens only at the surface, whereas boiling occurs throughout the liquid.
  • Energy: Evaporation is a slow process, while boiling is rapid and involves bubble formation.

Factors Affecting Evaporation:

  • Temperature: Higher temperatures increase the rate of evaporation as particles gain more kinetic energy.
  • Surface Area: Larger surface areas expose more liquid particles to the air, speeding up evaporation.
  • Humidity: Lower humidity levels allow faster evaporation because the air can absorb more vapour.
  • Wind Speed: Moving air carries away vapour particles, increasing the evaporation rate.

Understanding evaporation is crucial in daily life, such as in cooling mechanisms (e.g., sweating) and the water cycle.

Question 18:
Explain the process of evaporation with examples from daily life. How does it differ from boiling? Discuss the factors affecting the rate of evaporation.
Answer:

Evaporation is the process by which a liquid changes into its vapour state at any temperature below its boiling point. Unlike boiling, evaporation occurs only at the surface of the liquid and does not involve the formation of bubbles.


Examples from daily life:

  • Drying of clothes in the sun.
  • Cooling effect of sweating on our skin.
  • Disappearance of water from a wet floor.

Difference between evaporation and boiling:

  • Evaporation occurs at all temperatures, while boiling occurs at a fixed temperature (boiling point).
  • Evaporation is a surface phenomenon, whereas boiling involves the entire liquid.
  • Evaporation is a slow process, while boiling is rapid.

Factors affecting the rate of evaporation:

  • Temperature: Higher temperature increases evaporation.
  • Surface area: Larger surface area speeds up evaporation.
  • Humidity: Lower humidity promotes faster evaporation.
  • Wind speed: Higher wind speed enhances evaporation.

Understanding these concepts helps explain phenomena like the cooling effect of evaporation and the drying of wet surfaces.

Question 19:
Describe the interconversion of states of matter with the help of a labelled diagram. Explain how latent heat plays a role in these changes.
Answer:

The interconversion of states of matter refers to the transformation of a substance from one state (solid, liquid, gas) to another due to changes in temperature or pressure. Below is a brief explanation with key processes:


Processes involved:

  • Melting: Solid to liquid (e.g., ice to water).
  • Freezing: Liquid to solid (e.g., water to ice).
  • Vaporization: Liquid to gas (e.g., boiling water).
  • Condensation: Gas to liquid (e.g., dew formation).
  • Sublimation: Solid directly to gas (e.g., dry ice).
  • Deposition: Gas directly to solid (e.g., frost formation).

Role of latent heat:

Latent heat is the energy absorbed or released during a state change without a temperature change.

  • Latent heat of fusion: Energy required to melt a solid into a liquid.
  • Latent heat of vaporization: Energy required to convert a liquid into a gas.

For example, when ice melts, it absorbs latent heat to break intermolecular bonds, but its temperature remains at 0°C until fully melted.

Question 20:
Explain the process of sublimation with a suitable example. How does this phenomenon demonstrate the kinetic theory of matter?
Answer:

Sublimation is the process where a solid directly changes into a gas without passing through the liquid state. This occurs when the particles of a solid gain enough energy to overcome the forces of attraction and escape into the gaseous phase.


Example: When solid ammonium chloride is heated, it directly converts into a white vapor without melting. Upon cooling, these vapors re-solidify on the cooler parts of the container.


Connection to Kinetic Theory: The kinetic theory of matter states that particles are in constant motion. During sublimation, solid particles absorb heat energy, vibrate faster, and break free from their fixed positions, transitioning directly to the gaseous state. This shows that intermolecular forces in solids can be overcome by sufficient energy input.


Application: Sublimation is used in air fresheners (solid to gas) and freeze-drying food (removing ice by sublimation in a vacuum).

Question 21:
Describe an activity to demonstrate that particles of matter are continuously moving. Include observations, inference, and a labeled diagram.
Answer:

Activity: Dissolving potassium permanganate in water.


Procedure:
1. Take a beaker filled with water.
2. Add a few crystals of potassium permanganate (purple-colored) at one corner without stirring.
3. Observe the changes over time.


Observations:
- The purple color slowly spreads throughout the water, even without stirring.
- After some time, the entire solution turns uniformly purple.


Inference: The movement of potassium permanganate particles in water proves that:
- Particles of matter (solutes and solvents) are in constant motion (Brownian motion).
- Intermixing occurs due to diffusion, where particles move from higher to lower concentration.


Diagram (Description):
1. Draw a beaker with water and crystals at the bottom.
2. Show purple streaks radiating outward, indicating diffusion.
3. Label the solute (potassium permanganate) and solvent (water).


Real-life Example: The smell of perfume spreading in a room follows the same principle.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A student observed that solid carbon dioxide (dry ice) directly changes to gas without melting. Name the process and explain why it occurs. Also, give one real-life application of this phenomenon.
Answer:
Case Summary

Dry ice skips the liquid phase and turns directly into gas.


Scientific Principle

This is sublimation, where a solid changes to gas without becoming liquid. It happens because CO₂ has weak intermolecular forces.


Solution Approach
  • Process: Sublimation (NCERT example: Camphor)
  • Application: Used in cold storage for preserving food.
Question 2:
Water droplets form on the outer surface of a cold drink bottle. Identify the process and explain why it happens. How does this relate to the states of matter?
Answer:
Case Summary

Condensation occurs when water vapor turns to liquid on a cold surface.


Scientific Principle

It happens because air’s water vapor loses energy and condenses (NCERT: Dew formation).


Solution Approach
  • Process: Condensation (gas → liquid)
  • States of matter: Shows interconversion between gas and liquid.
Question 3:
A balloon filled with hydrogen gas rises, but one filled with carbon dioxide sinks. Explain this using the concept of density. Give another example of this principle.
Answer:
Case Summary

Gases with different densities behave differently in air.


Scientific Principle

Hydrogen is less dense than air, so it rises (NCERT: Helium balloons). CO₂ is denser, so it sinks.


Solution Approach
  • Reason: Density difference (H₂: 0.09 g/L, CO₂: 1.98 g/L)
  • Example: Hot air balloons use warm, less dense air.
Question 4:
During evaporation, a liquid cools. Why does this happen? How is this principle used in coolers? Compare it with an NCERT example.
Answer:
Case Summary

Evaporation causes cooling due to energy absorption.


Scientific Principle

High-energy molecules escape, lowering the liquid’s temperature (NCERT: Sweat cools the body).


Solution Approach
  • Reason: Energy loss during phase change
  • Application: Desert coolers use water evaporation to cool air.
Question 5:
A student observes that dry ice disappears over time without leaving any residue. Explain sublimation using this example and compare it with the evaporation of water.
Answer:
Case Summary

Dry ice (solid CO2) directly converts to gas without melting, a process called sublimation.

Scientific Principle
  • Sublimation: Solid → Gas (e.g., camphor, NCERT example).
  • Evaporation: Liquid → Gas (e.g., water drying).
Solution Approach

Both involve state change, but sublimation skips the liquid phase. Our textbook shows naphthalene balls as another example.

Question 6:
A farmer spreads manure in fields, noticing its smell travels faster on a windy day. Relate this to diffusion and list two factors affecting it.
Answer:
Case Summary

Wind carries manure odor particles farther, demonstrating diffusion in gases.

Scientific Principle
  • Diffusion: Movement of particles from high → low concentration (NCERT: ink in water).
  • Factors: Temperature, wind (kinetic energy).
Solution Approach

Higher temperature/wind increases particle speed, speeding diffusion. Perfume spreading is a real-world example.

Question 7:
An ice cube melts faster when crushed. Analyze how surface area influences the rate of evaporation with another example.
Answer:
Case Summary

Crushed ice has more surface area exposed to heat, melting faster.

Scientific Principle
  • Larger surface area → faster evaporation (NCERT: clothes dry faster when spread out).
Solution Approach

More particles interact with surroundings. Real-world example: Sugar dissolves quicker when powdered.

Question 8:
A thermometer shows different temperatures for water and steam at 100°C. Explain this observation using latent heat.
Answer:
Case Summary

Steam at 100°C has higher energy than water at the same temperature due to latent heat.

Scientific Principle
  • Latent heat: Energy absorbed during state change without temperature rise (NCERT: boiling water).
Solution Approach

Steam stores extra energy to break bonds during vaporization. Real-world example: Burns from steam are more severe than boiling water.

Question 9:
A student observed that naphthalene balls kept in a closet disappear after a few weeks without leaving any residue. Explain this phenomenon using the concept of sublimation and give one NCERT example.
Answer:
Case Summary

Naphthalene balls vanish due to sublimation, changing directly from solid to gas.

Scientific Principle
  • Sublimation is the transition of a substance from solid to gas without becoming liquid.
Solution Approach

Our textbook shows iodine crystals subliming when heated. Similarly, naphthalene sublimates at room temperature, explaining its disappearance.

Question 10:
During a lab experiment, water droplets formed on the outer surface of a cold drink bottle. Identify the process and relate it to the water cycle with an NCERT example.
Answer:
Case Summary

Droplets form due to condensation of water vapor on the cold surface.

Scientific Principle
  • Condensation occurs when gas turns to liquid upon cooling.
Solution Approach

Our textbook mentions dew forming on grass. Here, water vapor in air condenses on the cold bottle, similar to the water cycle where clouds form.

Question 11:
A farmer spreads water on the road during hot summer days. Analyze how this cools the surroundings using the concept of latent heat and an NCERT example.
Answer:
Case Summary

Water absorbs heat from the road to evaporate, cooling the area.

Scientific Principle
  • Latent heat is the energy absorbed during phase change without temperature rise.
Solution Approach

Our textbook shows sweat cooling the body. Similarly, water uses latent heat of vaporization to evaporate, reducing road temperature.

Question 12:
An ice cube melts faster when crushed than as a whole. Explain why using the concept of surface area and give one real-world application.
Answer:
Case Summary

Crushed ice has more surface area exposed to heat, melting faster.

Scientific Principle
  • Increased surface area enhances heat transfer.
Solution Approach

Our textbook demonstrates sugar dissolving faster in powdered form. Similarly, surface area affects melting. Real-world example: Quick-cooling drinks with crushed ice.

Question 13:

Rahul observed that when he poured 50 mL of water into a beaker, it took the shape of the beaker. However, when he placed an ice cube in another beaker, it retained its shape. Based on these observations:

  • Identify the states of matter involved in both cases.
  • Explain the difference in behavior using the kinetic theory of matter.
Answer:

The two states of matter observed are liquid (water) and solid (ice).

According to the kinetic theory of matter:

  • In liquids, particles have moderate kinetic energy and can move past each other, allowing the liquid to flow and take the shape of its container.
  • In solids, particles have very low kinetic energy and are tightly packed in a fixed arrangement, giving them a definite shape and volume.

Thus, water flows due to weaker intermolecular forces, while ice retains its shape due to strong intermolecular forces and fixed positions of particles.

Question 14:

Priya noticed that when she sprayed perfume in one corner of her room, the fragrance spread throughout the room after some time. Answer the following:

  • Name the phenomenon responsible for this observation.
  • Explain how this phenomenon occurs at the particle level.
Answer:

The phenomenon observed is diffusion.

At the particle level:

  • Perfume particles have high kinetic energy and move randomly in all directions.
  • They collide with air particles, gradually spreading from a region of higher concentration (where sprayed) to lower concentration (rest of the room).
  • This happens because gases have weak intermolecular forces and large spaces between particles, allowing easy movement.

Diffusion is faster in gases than liquids or solids due to greater particle mobility.

Question 15:

Rahul observed that when he poured 50 mL of water into a beaker, it took the shape of the container. However, when he placed an ice cube of the same volume in another beaker, it retained its shape. Based on this observation:

  • Identify the states of matter involved in the activity.
  • Explain the difference in behavior between water and ice using the kinetic theory of matter.
Answer:

The states of matter involved are liquid (water) and solid (ice).

According to the kinetic theory of matter:

  • In liquids, particles have moderate kinetic energy and can move past one another, allowing the liquid to flow and take the shape of its container.
  • In solids, particles have very low kinetic energy and are tightly packed in a fixed arrangement, giving solids a definite shape and volume.

Thus, water flows and adapts to the beaker's shape, while ice retains its rigid structure.

Question 16:

Priya conducted an experiment where she heated a closed container filled with a gas. She noticed that the pressure inside the container increased. Using this scenario:

  • Name the law that explains this observation.
  • Describe how the motion of gas particles changes with heating and its effect on pressure.
Answer:

The observation is explained by Gay-Lussac's Law, which states that the pressure of a gas is directly proportional to its temperature at constant volume.

When the gas is heated:

  • The kinetic energy of gas particles increases, causing them to move faster.
  • These faster-moving particles collide more frequently and with greater force against the container walls.
  • This results in an increase in pressure inside the container.

Thus, heating a gas in a closed system leads to higher pressure due to increased particle motion.

Question 17:
Rahul observed that when he poured 50 mL of water into a beaker, it took the shape of the container. However, when he placed an ice cube in another beaker, it retained its shape. Based on these observations, answer the following:
(a) Why does water take the shape of the container while ice does not?
(b) What property of matter is demonstrated here? Explain.
Answer:

(a) Water takes the shape of the container because it is a liquid, where particles have more freedom to move and slide past each other, allowing the liquid to flow and adapt to the container's shape. Ice, being a solid, has a rigid structure with particles tightly packed in fixed positions, so it retains its shape.


(b) The property demonstrated here is the intermolecular force and kinetic energy of particles. In solids, strong intermolecular forces hold particles in place, while in liquids, weaker forces allow movement. This difference explains the behavior of ice and water.

Question 18:
During a chemistry experiment, Priya noticed that when she heated a solid substance in a closed container, it directly turned into a gas without passing through the liquid state.
(a) Name the process observed by Priya.
(b) Give two examples of substances that exhibit this process at room temperature.
Answer:

(a) The process observed is called sublimation, where a solid directly converts into gas without becoming a liquid.


(b) Two examples of substances that sublime at room temperature are:

  • Camphor - It slowly changes from solid to gas, leaving no residue.
  • Iodine - When heated, it forms purple vapors without melting.
This property is useful in applications like air fresheners and dry ice (solid CO2).

Question 19:
Rahul observed that when he added a few drops of ink to a glass of water, the ink spread uniformly throughout the water without stirring. Based on this observation, answer the following:
(a) Name the phenomenon responsible for this observation.
(b) Explain why this phenomenon occurs in liquids but not in solids.
Answer:

(a) The phenomenon observed is called diffusion. It is the movement of particles from a region of higher concentration to a region of lower concentration until they are evenly distributed.

(b) Diffusion occurs in liquids because the particles in liquids have more intermolecular space and kinetic energy compared to solids. This allows them to move freely and mix. In solids, particles are tightly packed with very little intermolecular space and negligible kinetic energy, making diffusion almost impossible under normal conditions.

Question 20:
During a school experiment, Priya noticed that when she heated a beaker of water, bubbles formed at the bottom before the water started boiling. Answer the following based on her observation:
(a) What do these bubbles contain?
(b) Why do these bubbles form only at the bottom initially and not throughout the liquid?
Answer:

(a) The bubbles contain water vapor (or steam) formed due to the evaporation of water at high temperatures.

(b) Bubbles form at the bottom initially because the bottom of the beaker is in direct contact with the heat source, making it the hottest part. The water at the bottom gains enough kinetic energy to change into vapor, forming bubbles. The upper layers of water are still cooler, so vaporization doesn’t occur there until the entire liquid reaches its boiling point.

Question 21:
Rahul observed that when he sprayed deodorant in his room, the fragrance spread quickly to all corners. His friend suggested that this happens because gases have high compressibility. However, Rahul disagreed and said it is due to diffusion. Who is correct? Justify your answer with a detailed explanation of the phenomenon involved.
Answer:

Rahul is correct. The spreading of fragrance is due to diffusion, not compressibility. Diffusion is the process by which particles of a substance move from an area of higher concentration to an area of lower concentration until they are evenly distributed.


In gases, particles move rapidly and randomly due to high kinetic energy, allowing them to mix easily with air molecules. This is why the fragrance spreads quickly.


Compressibility, on the other hand, refers to the ability of a substance to reduce its volume under pressure, which is unrelated to the spreading of fragrance.

Question 22:
A student placed a drop of blue ink in a beaker of water and observed that the entire water turned blue after some time. She also noticed that the process was faster in hot water compared to cold water. Explain the phenomenon involved and the reason behind the difference in the rate of color change.
Answer:

The phenomenon observed is diffusion, where particles of ink move from a region of higher concentration (the drop) to lower concentration (water) until uniformly distributed.


The process is faster in hot water because:

  • Particles gain more kinetic energy at higher temperatures, moving faster.
  • Increased collisions between ink and water molecules speed up mixing.

In cold water, particles have less energy, so diffusion occurs slower. This demonstrates the effect of temperature on the rate of diffusion.

Chat on WhatsApp