1. Physical Nature of Matter
- Matter: Anything that has mass and occupies space.
- All things around us — air, water, food, stones — are forms of matter.
Important Points:
- Matter is made up of particles.
- Particles of matter are very small. They are not visible to the naked eye and cannot be broken down further by physical means.
Activity:
- Dissolve a few crystals of potassium permanganate in water → solution appears purple.
- Repeat dilution → purple colour is still visible → proves particles are small and continuously spread.
2. Characteristics of Particles of Matter
| Characteristic | Explanation |
|---|---|
| 1. Particles of matter have space | Intermolecular spaces exist → seen in mixing sugar in water. |
| 2. Particles are continuously moving | Shown by diffusion of ink or fragrance of perfume in air. |
| 3. Particles attract each other | Attractive forces hold particles together → shown by difficulty in breaking solids. |
3. Particles of Matter Attract Each Other
- There are forces of attraction between particles of matter.
- This force is:
- Strongest in solids
- Moderate in liquids
- Weakest in gases
Examples:
- Solids are hard to compress or break → strong attraction.
- Gases can be compressed easily → weak attraction.
4. States of Matter
There are 3 primary states of matter:
- Solid
- Liquid
- Gas
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | No fixed shape (takes container’s shape) | No fixed shape |
| Volume | Fixed | Fixed | Not fixed |
| Compressibility | Negligible | Slightly compressible | Highly compressible |
| Flow | Cannot flow | Can flow | Can flow freely |
| Particle attraction | Strong | Moderate | Weak |
| Inter-particle space | Very small | Moderate | Large |
| Kinetic energy | Very low | Moderate | High |
Note: A 4th state of matter — Plasma — exists in stars and lightning.
5. Can Matter Change Its State?
Yes, matter can change from one state to another by changing:
- Temperature
- Pressure
Processes Involved:
| Change of State | Process Name |
|---|---|
| Solid → Liquid | Melting/Fusion |
| Liquid → Gas | Boiling/Vaporisation |
| Gas → Liquid | Condensation |
| Liquid → Solid | Freezing/Solidification |
| Solid → Gas | Sublimation |
| Gas → Solid | Deposition |
Important Terms:
- Melting Point: Temp. at which a solid turns into a liquid.
- Boiling Point: Temp. at which a liquid turns into gas.
- Latent Heat: Heat energy required to change the state without changing temperature.
- Latent heat of fusion: Solid to liquid
- Latent heat of vaporisation: Liquid to gas
Effect of Pressure:
- Increasing pressure can turn gas into liquid.
- Example: LPG cylinders – propane/butane gas is compressed into liquid under high pressure.
6. Evaporation
Evaporation: Process by which a liquid changes into vapor at any temperature below its boiling point.
Factors Affecting Evaporation:
| Factor | Effect |
|---|---|
| Surface area | Larger surface → faster evaporation |
| Temperature | Higher temp → more kinetic energy → faster evaporation |
| Humidity | More humidity → slower evaporation |
| Wind speed | Higher wind speed → faster evaporation |
Examples:
- Wet clothes dry faster on a windy day.
- Water cools in earthen pots due to evaporation.
How Does Evaporation Cause Cooling?
- During evaporation, the particles absorb energy from surroundings to overcome intermolecular force.
- This leads to cooling effect.
Example: Rubbing alcohol or acetone feels cool on the skin.
Extra Facts to Remember:
- Interconversion of states of matter is a physical change, not a chemical change.
- Dry ice: Solid carbon dioxide. It sublimes directly to gas.
Diagram Suggestions (for your notebook):
- Kinetic energy vs State of Matter
- Arrangement of particles in solids, liquids, and gases
- Heating curve of water showing latent heats
- Interconversion flowchart of the three states
Textbook Questions and Answers
1. Convert the following temperatures to the Celsius scale.
(a) 293 K
(b) 470 K
Formula: °C = K – 273
✅ Answers:
(a) 293 K = 293 – 273 = 20°C
(b) 470 K = 470 – 273 = 197°C
2. Convert the following temperatures to the Kelvin scale.
(a) 25°C
(b) 373°C
Formula: K = °C + 273
✅ Answers:
(a) 25°C = 25 + 273 = 298 K
(b) 373°C = 373 + 273 = 646 K
3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
✅ Answer:
Naphthalene undergoes sublimation, i.e., it directly changes from solid to gas without becoming liquid. Hence, it disappears without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
✅ Answer:
Perfume particles diffuse into the air and spread due to the motion of gas particles, allowing the smell to reach a person sitting several metres away.
4. Arrange the following substances in increasing order of forces of attraction between the particles – water, sugar, oxygen.
✅ Answer:
Oxygen < Water < Sugar
(Reason: Gases < Liquids < Solids in terms of force of attraction)
5. What is the physical state of water at—
(a) 25°C
(b) 0°C
(c) 100°C?
✅ Answers:
(a) At 25°C → Liquid
(b) At 0°C → Solid + Liquid (both states coexist during melting)
(c) At 100°C → Liquid + Gas (both states coexist during boiling)
6. Give two reasons to justify—
(a) Water at room temperature is a liquid.
✅ Answer:
- Water has no fixed shape but has a fixed volume.
- It can flow, a characteristic of liquids.
(b) An iron almirah is a solid at room temperature.
✅ Answer:
- It has a definite shape and volume.
- It is rigid and incompressible, which are solid properties.
7. Why is ice at 273 K more effective in cooling than water at the same temperature?
✅ Answer:
Ice at 273 K absorbs latent heat of fusion from the surroundings to change into water at 273 K, thus causing more cooling than water at the same temperature.
8. What produces more severe burns, boiling water or steam?
✅ Answer:
Steam produces more severe burns because it contains the latent heat of vaporisation. This extra energy makes it more harmful than boiling water.
9. Name A, B, C, D, E and F in the following diagram showing change in its state.
Diagram Process Explanation:
textCopyEdit Increase heat & decrease pressure
-------------------------------------
| |
SOLID --A--> LIQUID --B--> GAS
^ | ^
| ↓ |
D <-------------F------------- C
↓ ↑
Decrease heat & increase pressure E
✅ Answer:
| Symbol | Process |
|---|---|
| A | Melting |
| B | Vaporisation |
| C | Condensation |
| D | Freezing |
| E | Sublimation |
| F | Deposition |
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📘 Chapter at a Glance: Matter in Our Surroundings
- Matter is anything that has mass and occupies space.
- Matter is made up of tiny particles.
- Particles of matter are constantly moving, attract each other, and have space between them.
- States of matter – Solid, Liquid, Gas.
- Matter can change its state by changing temperature or pressure.
- Melting, boiling, condensation, freezing, sublimation, and deposition are different interconversions of states.
- Evaporation is the surface phenomenon where particles escape from the surface of a liquid to form vapour.
- Factors affecting evaporation: surface area, temperature, humidity, and wind speed.
- Latent heat of fusion and latent heat of vaporisation are hidden energies required for phase change without changing temperature.
- Kelvin scale is the SI unit for temperature; 273 K = 0°C.
🧠 Key Terms
| Term | Definition |
|---|---|
| Matter | Anything that occupies space and has mass |
| Diffusion | Spontaneous intermixing of particles of two substances |
| Sublimation | Change of solid directly into gas without becoming liquid |
| Latent Heat | Heat required to change the state without temperature change |
| Evaporation | Conversion of liquid into vapour at surface at any temperature |
| Boiling | Rapid conversion of liquid to gas at boiling point |
| Melting Point | Temperature at which solid changes to liquid |
| Freezing Point | Temperature at which liquid turns into solid |
| Vaporisation | Conversion of liquid to gas |
| Condensation | Conversion of gas into liquid |
✅ 15 MCQs with Answers
- Matter is made up of:
a) Large particles
b) Atoms
c) Tiny particles ✅
d) None of these - Which of the following has the highest kinetic energy?
a) Ice
b) Water
c) Steam ✅
d) Salt - Which state of matter has a definite shape and volume?
a) Solid ✅
b) Liquid
c) Gas
d) Plasma - The conversion of gas to liquid is called:
a) Boiling
b) Condensation ✅
c) Melting
d) Freezing - Which of the following undergoes sublimation?
a) Ice
b) Water
c) Naphthalene ✅
d) Milk - The SI unit of temperature is:
a) Celsius
b) Fahrenheit
c) Kelvin ✅
d) Joule - Which process causes cooling?
a) Boiling
b) Evaporation ✅
c) Melting
d) Condensation - Particles of matter are:
a) Stationary
b) Randomly arranged
c) Continuously moving ✅
d) Fixed in place - Interconversion of states of matter is possible by changing:
a) Volume
b) Mass
c) Temperature and pressure ✅
d) Shape - Latent heat of vaporisation is required to convert:
a) Solid to liquid
b) Liquid to gas ✅
c) Gas to liquid
d) Liquid to solid - At 0°C, water exists as:
a) Only liquid
b) Only solid
c) Solid and liquid ✅
d) Gas - Diffusion is fastest in:
a) Solids
b) Liquids
c) Gases ✅
d) None - Boiling is a:
a) Surface phenomenon
b) Bulk phenomenon ✅
c) Constant phenomenon
d) Reversible phenomenon - Evaporation causes:
a) Heating
b) Cooling ✅
c) No effect
d) Melting - Which factor does not affect evaporation?
a) Temperature
b) Wind speed
c) Humidity
d) Pressure ✅
🔄 Match the Following
| A | B |
|---|---|
| 1. Solid → | (c) Fixed shape and volume |
| 2. Liquid → | (a) Flows, fixed volume |
| 3. Gas → | (d) No fixed shape or volume |
| 4. Sublimation → | (b) Solid to gas |
| 5. Condensation → | (e) Gas to liquid |
✅ Answers:
1 → c, 2 → a, 3 → d, 4 → b, 5 → e
❓ True and False
- Gases are compressible. ✅ True
- Melting is the process of liquid to solid. ❌ False
- Solids have high compressibility. ❌ False
- Water boils at 373 K. ✅ True
- Sublimation is observed in camphor. ✅ True
- Evaporation occurs only at boiling point. ❌ False
- Particles of matter are at rest. ❌ False
- Steam contains more energy than boiling water. ✅ True
- Diffusion occurs in solids, liquids, and gases. ✅ True
- Air is a pure substance. ❌ False
✍️ 10 Short Answer Questions with Answers
- What is matter?
👉 Matter is anything that has mass and occupies space. - Name the three states of matter.
👉 Solid, Liquid, Gas - What is diffusion?
👉 The intermixing of particles of two substances on their own is diffusion. - Define sublimation.
👉 Sublimation is the change of solid directly into gas without becoming liquid. - Give one example of sublimation.
👉 Naphthalene, camphor. - Define evaporation.
👉 Evaporation is the process by which liquid changes into gas at any temperature below its boiling point. - What is latent heat?
👉 Heat absorbed or released during a change of state without changing temperature. - What is the boiling point of water in Kelvin?
👉 373 K - Which factors affect evaporation?
👉 Surface area, temperature, humidity, wind speed. - Which has more energy: ice or water at 0°C?
👉 Water at 0°C
✍️ Long Answer Questions with Answers
1. Describe the characteristics of the particles of matter.
✅ Answer:
Particles of matter have the following characteristics:
- They have space between them.
- They are continuously moving.
- They attract each other.
- The amount of space and force of attraction varies with the state of matter.
2. Explain the states of matter with properties.
✅ Answer:
There are three states of matter:
1. Solids
- Definite shape and volume
- Incompressible
- Tightly packed particles
- Least kinetic energy
2. Liquids
- No fixed shape but fixed volume
- Flow easily
- Less tightly packed than solids
- More kinetic energy than solids
3. Gases
- No fixed shape or volume
- Highly compressible
- Particles far apart
- Highest kinetic energy
3. Explain how matter changes its state.
✅ Answer:
Matter changes its state due to:
- Change in temperature:
Heating a solid increases kinetic energy, causing it to melt (solid to liquid) and then boil (liquid to gas). - Change in pressure:
Increasing pressure can compress gases into liquids. For example, LPG is stored under high pressure in cylinders.