Matter in Our Surroundings — Previous Year Questions (Class 9 Science)
Explore the nature of matter, its properties, and states. Understand the characteristics of solids, liquids, and gases, and how they change under different
TL;DR: Explore the nature of matter, its properties, and states. Understand the characteristics of solids, liquids, and gases, and how they change under diff…
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Explore the nature of matter, its properties, and states. Understand the characteristics of solids, liquids, and gases, and how they change under different
Matter in Our Surroundings — Previous Year Questions with Solutions
Q (2023, 2 marks): Define matter and state its three main states. Give one example of each state.
Answer: Matter:
Definition: Anything that occupies space and has mass is called matter.
Three main states of matter:
1. Solid:
- Fixed shape and fixed volume
- Particles are closely packed
- Example: Iron, Wood, Stone
2. Liquid:
- Fixed volume but no fixed shape (takes shape of container)
- Particles are less tightly packed than solids
- Example: Water, Oil, Milk
3. Gas:
- No fixed shape and no fixed volume
- Particles are very loosely packed
- Example: Oxygen, Nitrogen, Carbon Dioxide
Q (2022, 3 marks): Explain the process of evaporation and give two examples of it in daily life.
Answer: Evaporation:
Definition: Evaporation is the process in which a liquid changes into its gaseous state at any temperature below its boiling point.
Characteristics:
- Occurs at the surface of the liquid
- Requires thermal energy (heat)
- Endothermic process (absorbs heat)
- Rate increases with temperature, humidity, and wind
- Faster for substances with lower boiling points
Daily Life Examples:
1. Drying of Clothes:
Wet clothes placed in the sun dry because water evaporates from them.
2. Evaporation of Sweat:
When we sweat, the perspiration on our skin evaporates, cooling our body.
Other examples: Evaporation of water from puddles after rain, evaporation of water from plants' leaves
Q (2024, 2 marks): What is the difference between melting and boiling?
Answer: Melting:
- Process: Solid changes to liquid
- Temperature: Occurs at a fixed temperature called melting point
- Only at surface: No, occurs throughout the substance
- Occurs naturally: Yes, when solid is heated
- Example: Ice melting to water at 0°C
Boiling:
- Process: Liquid changes to gas
- Temperature: Occurs at a fixed temperature called boiling point
- Throughout substance: Rapid, occurs throughout the liquid
- Requires heating: Yes, must be heated to boiling point
- Example: Water boiling to steam at 100°C
Both are phase changes that require heat energy to occur
Q (2023, 3 marks): Explain condensation and sublimation with one example each.
Answer: Condensation:
Definition: Condensation is the process in which a gas changes into a liquid upon cooling.
Characteristics:
- Reverse process of evaporation and boiling
- Releases heat energy (exothermic)
- Occurs when thermal energy decreases
Example: Formation of Dew
Water vapor in air condenses during cooler nights to form water droplets (dew) on grass and leaves.
Other example: Steam from boiling water condenses on a cold mirror
Sublimation:
Definition: Sublimation is the process in which a solid changes directly into a gas without passing through the liquid state.
Characteristics:
- Rare process
- Occurs only in certain substances
- Requires significant heat energy
- Opposite is deposition (gas to solid)
Example: Dry Ice (Solid CO2)
Dry ice converts directly to carbon dioxide gas without melting to liquid.
Other example: Evaporation of mothballs (naphthalene) stored in wardrobes
Q (2022, 3 marks): Describe the characteristics of gases based on kinetic molecular theory.
Answer: Kinetic Molecular Theory of Gases:
Main Postulates:
1. Composition:
- Gases consist of very small particles (molecules or atoms)
- Volume of particles is negligible compared to container volume
2. Motion:
- Particles are in continuous, random motion
- Collisions are elastic (no energy loss)
3. Force:
- No intermolecular forces between particles
- Particles move independently
4. Energy:
- Average kinetic energy is proportional to absolute temperature
- KE = (3/2)kT (where k is Boltzmann constant)
Characteristics Explained:
1. No Fixed Shape or Volume:
- Gas particles fill the entire available space
2. High Compressibility:
- Large spaces between particles allow compression
3. Diffusion:
- Random motion causes mixing with other gases
4. Pressure:
- Caused by collisions of particles with container walls
5. Low Density:
- Few particles per unit volume
Q (2024, 2 marks): What happens when dry ice is exposed to the atmosphere?
Answer: Dry Ice (Solid CO2) Properties:
When dry ice is exposed to the atmosphere:
1. Sublimation:
- Dry ice converts directly into carbon dioxide gas
- Does not melt into liquid CO2
- Requires energy for this phase change
2. Temperature:
- Dry ice has temperature around -78.5°C
- Very cold, can cause burns if touched
3. Visible Effect:
- White smoke-like cloud forms
- This is water vapor from air condensing due to cold, not the CO2 itself
- CO2 gas is colorless and odorless
4. Why no liquid?
- CO2 sublimes at -78.5°C under normal atmospheric pressure
- Temperature is below sublimation point
- Liquid CO2 only exists under high pressure
Use: Dry ice is used to preserve frozen food and create stage effects
Frequently Asked Questions
Why does water evaporate faster on a hot day than on a cool day?
Evaporation rate increases with temperature because heat provides kinetic energy to molecules. On hot days, water molecules have more energy to overcome intermolecular forces and escape into the gaseous state. Higher temperature also increases the rate of molecular collisions at the surface.
Why is latent heat required during phase changes even when temperature remains constant?
During phase changes, heat energy is used to overcome intermolecular forces and rearrange the molecular structure, not to increase temperature. The heat is absorbed (or released) to change the state of matter. This is why the temperature of ice remains 0°C while melting, even though heat is being supplied.
More Class 9 Science PYQs
- Chemical Reactions and Equations
- Light (Reflection and Refraction)
- Electricity
- Acids, Bases and Salts
- Metals and Non-metals
- Life Processes
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