Matter in Our Surroundings
Detailed NCERT Solutions & Theory Notes
In-Text Questions (Page 3)
Q1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.
Answer: Matter is anything that has
mass and occupies space.
Matter: Chair, air, almonds, lemon water, smell of
perfume (due to volatile particles).
Not Matter: Love, smell (sensation), hate,
thought, cold.
Q2. Give reasons for the following observation: The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Answer: The smell reaches us due to the process of diffusion. The rate of diffusion increases with temperature because the kinetic energy of particles increases. Hot food particles possess high kinetic energy and thus diffuse faster into the air, reaching several meters away. Cold food releases particles with lower kinetic energy, so they do not diffuse far.
Q3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Answer: This observation shows that:
- The particles of matter have spaces between them (intermolecular space).
- The force of attraction between the particles of liquid (water) is not very strong, allowing the diver to break through them.
Q4. What are the characteristics of the particles of matter?
Answer: The main characteristics are:
- Particles of matter have space between them.
- Particles of matter are continuously moving.
- Particles of matter attract each other.
In-Text Questions (Page 6)
Q1. The mass per unit volume of a substance is called density. (density = mass/volume). Arrange the following in order of increasing density: air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Answer: Increasing order of density:
Air < Exhaust from chimneys < Cotton < Water < Honey < Chalk < Iron
(Note: Cotton is solid but has large air spaces, making it less dense than liquids. Exhaust contains solid particles, making it denser than pure air.)
Q2. (a) Tabulate the differences in the characteristics of states of matter.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed shape | No fixed shape (takes shape of container) | No fixed shape |
| Volume | Fixed volume | Fixed volume | No fixed volume |
| Compressibility | Negligible | Low | High |
| Intermolecular Force | Maximum | Less than solids | Minimum |
| Fluidity | Rigid (cannot flow) | Can flow (fluid) | Flows easily (fluid) |
Main Textbook Exercises
Q1. Convert the following temperatures to the celsius scale. (a) 293 K (b) 470 K
Formula: C = K - 273
(a) 293 - 273 = 20°C
(b) 470 - 273 = 197°C
Q2. Convert the following temperatures to the Kelvin scale. (a) 25°C (b) 373°C
Formula: K = C + 273
(a) 25 + 273 = 298 K
(b) 373 + 273 = 646 K
Q3. Give reason for the following observations: (a) Naphthalene balls disappear with time without leaving any solid. (b) We can get the smell of perfume sitting several metres away.
(a) Naphthalene undergoes sublimation. It converts directly from solid to gas state at room temperature. Hence, it disappears without leaving any residue.
(b) Perfume contains volatile solvent that vaporizes easily and diffuses into air. Since gas molecules move at high speed, the smell reaches us quickly even at a distance.
Q4. Arrange the following substances in increasing order of forces of attraction between the particles: water, sugar, oxygen.
Order: Gas < Liquid < Solid
Oxygen (Gas) < Water (Liquid) < Sugar (Solid)
Q5. What is the physical state of water at: (a) 25°C (b) 0°C (c) 100°C?
(a) Liquid
(b) Solid (and liquid as it is melting point)
(c) Gas (and liquid as it is boiling point)
Q6. Give two reasons to justify: (a) water at room temperature is a liquid. (b) an iron almirah is a solid at room temperature.
(a) Water:
- It has a fixed volume but no fixed shape.
- It can flow (fluidity).
(b) Iron Almirah:
- It has a fixed shape and fixed volume.
- It is rigid and incompressible.
Q7. Why is ice at 273 K more effective in cooling than water at the same temperature?
Ice at 273 K (0°C) absorbs latent heat of fusion from the surroundings to melt into water. Water at 0°C does not absorb this extra heat. Therefore, ice absorbs more heat from the substance to be cooled, making it more effective.
Q8. What produces more severe burns, boiling water or steam?
Steam. Steam at 100°C contains extra energy in the form of latent heat of vaporization compared to boiling water at the same temperature. Hence, it causes more severe burns.
Matter in Our Surroundings
Detailed Chapter Analysis & Key Concepts
1. Physical Nature of Matter
Everything in this universe is made up of material which scientists have named "matter". The air we breathe, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand – each thing is matter.
Definition: Since early times, human beings have tried to understand their surroundings. Early Indian philosophers classified matter in the form of five basic elements – the "Panch Tatva" – air, earth, fire, sky and water.
Characteristics of Particles of Matter
- Particles has space between them: When we make tea, coffee or lemonade (nimbu paani), particles of one type of matter get into the spaces between particles of the other.
- Particles are continuously moving: Particles possess kinetic energy. As the temperature rises, particles move faster.
- Particles attract each other: This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another (Solid > Liquid > Gas).
2. States of Matter
Matter around us exists in three different states– solid, liquid and gas.
- Definite shape & volume.
- Negligible compressibility.
- Rigid structure.
- Tendency to maintain shape when subjected to outside force.
- No fixed shape, but fixed volume.
- Takes shape of container.
- Flows and changes shape (Fluid).
- Solids and gases can diffuse into liquids.
- Highly compressible.
- Particles move randomly at high speed.
- Gases exert pressure on walls of container due to collisions.
- Maximum diffusion rate.
Did You Know?
Plasma and Bose-Einstein Condensate (BEC) are considered the 4th and
5th states of matter. Plasma consists of super energetic and super excited particles (ionized gases).
BEC is formed by cooling a gas of extremely low density to super low temperatures.
3. Can Matter Change its State?
Effect of Change of Temperature
On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed.
- Melting Point: The minimum temperature at which a solid melts to become a liquid at atmospheric pressure. (Ice = 273.15 K).
- Boiling Point: The temperature at which a liquid starts boiling at the atmospheric pressure. (Water = 373 K).
- Sublimation: A change of state directly from solid to gas without changing into liquid state (e.g., Camphor, Ammonium chloride).
- Deposition: The direct change of gas to solid without changing into liquid.
Latent Heat
The word 'latent' means hidden. The heat energy which is used up in overcoming the forces of attraction between the particles during a change of state is called latent heat.
- Latent Heat of Fusion: Amount of heat energy required to change 1 kg of solid into liquid at atmospheric pressure at its melting point.
- Latent Heat of Vaporization: Amount of heat energy required to change 1 kg of liquid into gas at atmospheric pressure at its boiling point.
4. Evaporation
The phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.
Factors Affecting Evaporation
Rate increases with increase in surface area (e.g., spreading clothes to dry).
Rate increases with increase in temperature (more kinetic energy).
Rate decreases with increase in humidity (air already holds moisture).
Rate increases with increase in wind speed (particles move away).
How Evaporation Causes Cooling
In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings makes the surroundings cold.
Real Life Example: Why should we wear
cotton clothes in summer?
During summer, we perspire more. Cotton, being a good absorber of water
helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation. Evaporation causes
cooling, making us feel comfortable.
Key Facts & Definitions
50+ Important Points to Remember
Anything that has mass and occupies space is called matter.
Early Indian philosophers classified matter into five basic elements: Air, Earth, Fire, Sky, and Water.
Matter is made up of tiny particles.
Particles of matter have spaces between them.
Particles of matter are continuously moving and possess kinetic energy.
Particles of matter attract each other.
The intermixing of particles of two different types of matter on their own.
Rate of diffusion becomes faster with the increase in temperature.
Have a definite shape, distinct boundaries, and fixed volumes.
Solids have negligible compressibility.
Have no fixed shape but have a fixed volume.
Liquids maintain their volume but change shape; they flow as fluids.
Highly compressible as compared to solids and liquids.
Liquefied Petroleum Gas - fuel used in homes (compressed gas).
Compressed Natural Gas - fuel used in vehicles.
Force of attraction is maximum in solids.
Force of attraction is minimum in gases.
Density = Mass / Volume.
Kelvin (K).
0°C = 273.15 K (Rounded generally to 273 K).
Temperature at which solid melts to obey liquid at atmospheric pressure.
The process of melting (change of solid into liquid state).
Bulk phenomenon where liquid changes to vapor state.
373 K (100°C).
Heat energy hidden in the contents of the substance.
Heat required to convert 1 kg of solid into liquid at melting point.
Heat required to convert 1 kg of liquid into gas at boiling point.
Direct change of state from solid to gas (e.g., Camphor, Dry Ice).
Solid Carbon Dioxide (CO2). Stored under high pressure.
Direct change of gas to solid without becoming liquid.
Surface phenomenon where liquid turns to vapor below boiling point.
Evaporation occurs only at the surface, unlike boiling (bulk).
Increased surface area increases evaporation.
Increased temperature increases evaporation.
Increased humidity decreases evaporation.
Increased wind speed increases evaporation.
Evaporation causes cooling by absorbing energy from surroundings.
Poured on palm feels cool because it evaporates rapidly absorbing heat.
Water keeps cool due to evaporation through pores.
Absorb sweat and expose it for evaporation, keeping body cool.
Visible on outer surface containing ice cold water due to condensation of water vapor in air.
4th state of matter. Ionized gas with super energetic particles.
Contain neon gas which creates plasma when electricity flows.
Glow because of the presence of plasma created by high temperature.
5th state of matter (BEC). Formed at super low density and temperature.
Indian physicist who did calculations for the 5th state of matter.
Pascal (Pa). 1 atmosphere (atm) = 1.01 x 10^5 Pa.
The pressure of air at sea level.
The property of matter to maintain its shape against external force.
Energy possessed by particles due to their motion.