Vidaara.orgClass 9 · Chemistry
CodeC9-CHEM-1-CW
Chapter Assignment — Matter in Our Surroundings
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working and give reasons where asked. For full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
6 × 1 = 6 marks
1.
The state of matter with a fixed volume but no fixed shape is:
- A.solid
- B.liquid
- C.gas
- D.plasma
2.
Diffusion increases when the temperature is:
- A.lowered
- B.raised
- C.kept constant
- D.zero
3.
0°C is equal to:
- A.0 K
- B.100 K
- C.273 K
- D.373 K
4.
The hidden heat absorbed during a change of state is the:
- A.specific heat
- B.latent heat
- C.kinetic energy
- D.potential energy
5.
Evaporation is a:
- A.surface phenomenon
- B.bulk phenomenon
- C.form of boiling
- D.form of freezing
6.
Which factor decreases the rate of evaporation?
- A.higher temperature
- B.higher humidity
- C.higher wind speed
- D.larger surface area
Section B — Short Answer (2 marks)
4 × 2 = 8 marks
7.
State any two evidences that show particles of matter are continuously moving.
8.
Convert 40°C to Kelvin and 263 K to Celsius.
9.
Why does a desert cooler cool better on a hot, dry day?
10.
Define sublimation and give one example.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
11.
Compare the three states of matter on the basis of inter-particle spaces, force of attraction and arrangement of particles.
12.
Explain why the temperature of a substance does not change during its change of state.
Section D — Long Answer (5 marks)
2 × 5 = 10 marks
13.
Define evaporation. Explain how surface area, temperature, humidity and wind speed each affect its rate, and explain why evaporation produces cooling.
14.
Describe the heating of ice from below 0°C to steam, naming each change of state and identifying where latent heat is involved.
Answer Key
Section A — Multiple Choice Questions
- (B) liquid
- (B) raised
- (C) 273 K
- (B) latent heat
- (A) surface phenomenon
- (B) higher humidity
Section B — Short Answer (2 marks)
- The spreading of a smell (diffusion of gases) across a room, and the slow spreading of ink or potassium permanganate colour through still water, both show particles are in continuous motion.
- 40°C = 40 + 273 = 313 K; 263 K = 263 - 273 = -10°C.
- Low humidity and high temperature both increase the rate of evaporation of water in the cooler, which absorbs more heat from the air and cools it more effectively.
- Sublimation is the change of a solid directly into vapour without becoming a liquid; for example, camphor (or dry ice / ammonium chloride).
Section C — Short Answer (3 marks)
- Solid: very small spaces, very strong force, particles packed in fixed orderly positions. Liquid: larger spaces, moderate force, particles loosely arranged and able to slide. Gas: very large spaces, very weak force, particles far apart and randomly arranged.
- During a change of state the heat supplied is absorbed as latent heat to break the forces of attraction between particles, rather than to increase their kinetic energy. Since kinetic energy (which decides temperature) does not change, the temperature stays constant until the change of state is complete.
Section D — Long Answer (5 marks)
- Evaporation is the change of a liquid into vapour at a temperature below its boiling point, occurring only at the surface. Larger surface area increases the rate (more particles can escape); higher temperature increases the rate (more particles gain escape energy); higher humidity decreases the rate (the air is near saturation); higher wind speed increases the rate (vapour is carried away). Evaporation causes cooling because the fastest, most energetic particles escape, lowering the average kinetic energy of the remaining liquid, and the liquid absorbs latent heat from its surroundings to keep evaporating, thereby cooling them.
- As ice below 0°C is heated, its temperature rises to 0°C. At 0°C it melts to water (fusion), absorbing latent heat of fusion at constant temperature. The water then warms to 100°C. At 100°C it boils to steam (vaporisation), absorbing latent heat of vaporisation at constant temperature. Further heating raises the temperature of the steam. The two changes of state, melting and boiling, are where latent heat is absorbed and the temperature stays constant.
Generated by Vidaara.org · Assignment C9-CHEM-1-CW · vidaara.org