🔹 Very Short Answer Questions (1 Mark Each)
Q1. Define matter.
Ans. Anything that has mass and occupies space is called matter.
Q2. Name the three states of matter.
Ans. Solid, Liquid and Gas.
Q3. What is diffusion?
Ans. The intermixing of particles of two substances on their own is called diffusion.
Q4. Which state of matter has maximum kinetic energy?
Ans. Gaseous state.
Q5. Which state of matter has a definite shape and volume?
Ans. Solid.
Q6. What is the SI unit of temperature?
Ans. Kelvin (K).
Q7. Name one process that shows matter is made up of particles.
Ans. Dissolving potassium permanganate in water.
Q8. What is sublimation? Give one example.
Ans. The direct conversion of solid into gas without changing into liquid. Example: Camphor.
Q9. Name the process by which a liquid changes into vapour below its boiling point.
Ans. Evaporation.
Q10. Why do we feel cool after sweating?
Ans. Because sweat evaporates by taking heat from our body, producing a cooling effect.
🔹 Short Answer Questions (2–3 Marks Each)
Q11. Why is diffusion faster in gases than in liquids?
Ans. In gases, particles are far apart and move with high kinetic energy. This allows them to mix faster compared to liquids where particles are closer and move slowly.
Q12. Differentiate between evaporation and boiling.
Ans.
- Evaporation occurs at all temperatures, boiling occurs only at a fixed temperature.
- Evaporation is a surface phenomenon, boiling is a bulk phenomenon.
Q13. Why can gases be compressed but not solids?
Ans. Gases have large intermolecular spaces that can be reduced by pressure, but solids have tightly packed particles with negligible space, so they cannot be compressed.
Q14. State two factors that affect the rate of diffusion.
Ans. (i) Temperature (higher temperature → faster diffusion)
(ii) Density of medium (lower density → faster diffusion).
Q15. Why does a desert cooler cool better on a hot dry day?
Ans. On a hot dry day, the rate of evaporation is higher due to low humidity and high temperature. This increases cooling.
Q16. Why do we wear cotton clothes in summer?
Ans. Cotton absorbs sweat and exposes it to air. Sweat evaporates quickly, giving a cooling effect.
Q17. What is latent heat of vaporisation?
Ans. It is the heat energy required to convert 1 kg of liquid into vapour at its boiling point without changing temperature.
Q18. Differentiate between solids, liquids and gases (four points).
Ans.
- Solids: Definite shape & volume, incompressible, particles tightly packed.
- Liquids: No definite shape but definite volume, slightly compressible, particles slide over each other.
- Gases: Neither definite shape nor volume, highly compressible, particles move freely.
Q19. Why do wet clothes dry faster on a windy day?
Ans. Because wind increases the rate of evaporation by removing vapour from the surface.
Q20. Why does evaporation cause cooling?
Ans. During evaporation, particles absorb heat energy from surroundings to change into vapour, causing cooling.
🔹 Long Answer Questions (4–5 Marks Each)
Q21. Explain the main characteristics of particles of matter.
Ans.
- Matter is made up of particles.
- Particles of matter are very small in size.
- Particles have spaces between them.
- Particles are in continuous motion.
- Particles attract each other.
Q22. Explain the effect of temperature on the state of matter.
Ans. On heating, particles gain kinetic energy and overcome intermolecular forces:
- Solid → Liquid (melting)
- Liquid → Gas (vaporisation)
On cooling, reverse happens: - Gas → Liquid (condensation)
- Liquid → Solid (freezing).
Q23. What is sublimation? Give two examples.
Ans. Sublimation is the process in which a solid directly changes into gas without becoming liquid.
Examples: Camphor, naphthalene balls, dry ice.
Q24. Explain evaporation. State four factors affecting it.
Ans. Evaporation is the process of conversion of liquid into vapour at temperatures below its boiling point.
Factors affecting it:
- Temperature
- Surface area
- Wind speed
- Humidity
Q25. Why do solids have a definite shape but liquids and gases do not?
Ans. Solids have very strong intermolecular forces that keep particles in fixed positions → definite shape. Liquids and gases have weaker forces → particles move freely, so no definite shape.
Q26. Describe an activity to show that matter is made up of particles.
Ans. Add a small crystal of potassium permanganate into water. The entire water turns purple. This shows that tiny particles of KMnO₄ spread throughout, proving matter is made up of particles.
Q27. Describe an activity to show that particles of matter are continuously moving.
Ans. Put a drop of ink in water. The ink spreads slowly in water without stirring, showing that particles of matter are constantly moving.
Q28. Why do gases exert pressure on the walls of the container?
Ans. Gas particles move randomly and collide with container walls. The force exerted by these collisions per unit area is called pressure.
Q29. How do states of matter change on heating and cooling?
Ans.
- Heating: Solid melts into liquid → liquid vaporises into gas.
- Cooling: Gas condenses into liquid → liquid freezes into solid.
Q30. Write differences between melting and evaporation.
Ans.
- Melting: Solid changes to liquid at a fixed temperature.
- Evaporation: Liquid changes to vapour at all temperatures.
- Melting is bulk process; evaporation is surface phenomenon.
🔹 Case Study / Application-Based Questions
Q31. A few drops of perfume spread across the whole room in a short time.
Ans. This shows diffusion. It happens faster in summer because higher temperature increases particle movement.
Q32. A desert cooler works effectively in dry regions but not in humid regions. Why?
Ans. Because evaporation is faster in dry regions due to low humidity. In humid areas, evaporation slows down, so cooling is less.
Q33. Clothes dry faster when spread out. Why?
Ans. Larger surface area allows more water molecules to evaporate quickly.
Q34. When camphor is left in open, it disappears. Explain.
Ans. Camphor undergoes sublimation, directly converting from solid to vapour.
Q35. During summer, water kept in an earthen pot becomes cool. Why?
Ans. Water seeps out of the pot’s pores and evaporates, taking heat away and cooling the water.
Q36. Why does water kept in a tumbler form droplets on its outer surface in summer?
Ans. Water vapour in the air condenses on the cold surface of the tumbler.
Q37. Why is ice at 0°C colder than water at 0°C?
Ans. Ice contains latent heat of fusion, so it absorbs more heat from the surroundings before melting, making it feel colder.
Q38. Define freezing. Give one example.
Ans. Freezing is the process of conversion of liquid into solid at low temperature. Example: Water into ice.
Q39. What is condensation? Give one example.
Ans. Condensation is the process of conversion of gas into liquid. Example: Formation of dew.
Q40. Why does the smell of hot food reach us faster than cold food?
Ans. Because diffusion is faster at higher temperatures.
🔹 Additional Very Important Questions
Q41. Why does evaporation take place at all temperatures?
Ans. Because at any temperature, some particles of liquid always have enough energy to escape from the surface.
Q42. Name the temperature at which a liquid changes into vapour.
Ans. Boiling point.
Q43. Why does the level of water not change when ice melts in it?
Ans. Because the volume of water formed is equal to the volume of displaced ice.
Q44. Why are solids generally denser than liquids and gases?
Ans. Because particles in solids are closely packed, giving higher density.
Q45. Why are gases more easily compressed than liquids and solids?
Ans. Because intermolecular spaces in gases are very large.
Q46. Why is latent heat called “hidden heat”?
Ans. Because it is absorbed or released during change of state without any temperature change.
Q47. Why do naphthalene balls disappear when left in the open?
Ans. Because they undergo sublimation.
Q48. What happens to the movement of particles when temperature is lowered?
Ans. Their kinetic energy decreases, and they move slower.
Q49. Why does water vapour condense on the bathroom mirror while bathing with hot water?
Ans. Because the mirror’s cool surface converts vapour into tiny liquid droplets (condensation).
Q50. Why do gases have neither definite shape nor definite volume?
Ans. Because intermolecular forces are very weak, and particles move freely filling the entire container.