Class 9th Chapter 1 Matter in Our Surroundings

Class 9 Science - Matter in Our Surroundings

1. Convert the following temperatures to the Celsius scale:

Formula:

°C = K - 273

(a) 293 K = 20°C
(b) 470 K = 197°C

2. Convert the following temperatures to the Kelvin scale:

Formula:

K = °C + 273

(a) 25°C = 298 K
(b) 373°C = 646 K

3. Give reason for the following observations:

(a) Naphthalene balls disappear with time without leaving any solid because they undergo sublimation, changing directly from solid to gas.
(b) We can get the smell of perfume sitting several metres away because its particles diffuse through air, a property of gases.

4. Arrange the following substances in increasing order of forces of attraction between the particles — water, sugar, oxygen.

Increasing order: Oxygen < Water < Sugar.
Gases have the least force of attraction, liquids have more, and solids have the most.

5. What is the physical state of water at —

(a) 25°C – Liquid
(b) 0°C – Solid and liquid coexist
(c) 100°C – Liquid and gas coexist

6. Give two reasons to justify —

(a) Water at room temperature is a liquid because it flows and has no fixed shape but a fixed volume.
(b) An iron almirah is a solid at room temperature because it has a definite shape and volume and does not flow.

7. Why is ice at 273 K more effective in cooling than water at the same temperature?

Ice absorbs extra heat to melt (latent heat of fusion), which makes it more effective in cooling than water at 273 K.

8. What produces more severe burns, boiling water or steam?

Steam produces more severe burns than boiling water because it has more energy stored as latent heat of vaporization.

9. Name A, B, C, D, E and F in the following diagram showing change in its state:

A - Melting
B - Vaporization
C - Condensation
D - Freezing
E - Sublimation
F - Deposition